Marta Craveri

Anne-Marie Losonczy

Growing up in the Gulag: later accounts of deportation to the USSR

Keywords: history, childhood, gulag, deportation, memories, XXth Century, Europe, USSR

The authors

Directrice scientiique adjointe de la

Les Working Papers et les Position Papers de la Fondation Maison des sciences de l'homme ont pour objectif la difusion ouverte des travaux en train de se faire dans le cadre des diverses activités scientiiques de la Fondation : Le Collège d' études mondiales, Bourses Fernand Braudel-IFER, Programmes scientiiques, hébergement à la Maison Suger, Séminaires et Centres associés, Directeurs d'études associés... Les opinions exprimées dans cet article n' engagent que leur auteur et ne relètent pas nécessairement les positions institutionnelles de la Fondation MSH.

he Working Papers and Position Papers of the FMSH are produced in the course of the scientiic activities of the FMSH: the chairs of the Institute for Global Studies, Fernand Braudel-IFER grants, the Foundation's scientiic programmes, or the scholars hosted at the Maison Suger or as associate research directors. Working Papers may also be produced in partnership with ailiated institutions.

he views expressed in this paper are the author's own and do not necessarily relect institutional positions from the Foundation MSH.

Mots-clefs

histoire, enfance, goulag, déportation, mémoire, XXe siècle, Europe, URSS

Content

A host of deported children 5

Shattered childhoods 7

Separation and loss 7

Growing up in exile 11

Returning from exile 13 Some conclusions 14

T he earliest books about the labour camp system in the USSR to appear in the West after the Second World War were autobiographical 1 or collected testimonies 2 , written in a literary style and intended to bear witness and accuse.

For most historians, political scientists and sociologists [START_REF] Mcmillan | Signiicant exceptions are the works of Robert Conquest, Kolyma, he Artic Death camps[END_REF] , the almost complete absence of accessible written sources and the diiculty of acquiring oral testimony discouraged any systematic research into the mass purges in the USSR.

However, once the Soviet archives were opened, major research projects began to examine the Soviet concentration system, its origins on the Solovetsky Islands in the 1920s [START_REF] Michail | Origins of the Gulag. he Soviet Prison Camp System 1917-1934[END_REF] , its expansion into vast forestry, mining and industrial camps employing the ever-increasing numbers of victims of the purges of the 1930s and 1940s 5 , the various deportation operations throughout the Stalin period [START_REF] Polian | Against heir Will: he History and Geography of Forced Migrations in the USSR[END_REF] , the changes introduced during the War, the crisis in the entire post-War camp network 7 and the place of the Gulag in the social, political and economic life of the Soviet Union. 8 he historians' priority was the political, demographic and administrative aspects of the Gulag, and there has been little research into daily life in the camps and resettlement villages, and the diversity of people's experience of the Gulag. Only rarely have these topics been addressed with the tools of oral history, and they have usually been integrated into a historiographical approach based on archival sources. 9 he trajectory of children in the Soviet camps is a little-known aspect of this historical experience. One reason is that the archival documents available seldom mention them speciically. he few books that do 10 are either strictly national in scope or only deal with children in the labour camps; consequently, the history of the children forcibly deported with their families has not been seen as a research theme as such.

his contrasts markedly with the status of childhood in Holocaust research. Since the end of the Second World War, testimonies and historical research has made the lives of children deported to the concentration camps a central topic of study. 11 To expose this facet of Gulag history, a vital source is the systematic collection of recent oral testimonies. 12 Our European Memories of the 7. See Marta Craveri, "Forced Labour in the Soviet Union between 1939 and 1956", in Relexion on Gulag, eds. Elena Dundovich, Francesca Gori, Emanuela Guercetti (Milano: Annali della Fondazione Feltrinelli, 2003) 25-60. 8. See N. A. Adler, he Gulag Survivor Beyond the Soviet System (Somerset: Transaction Publishers, 2002); Paul R. Gregory and Valery Lazarev eds., he economics of forced labor. he Soviet Gulag (Stanford: California, Hoover Institution Press, 2003); M. Dobson, Khrushchev's Cold Summer. Gulag Returnees, Crime, and the Fate of Reform after Stalin (Ithaca: Cornell University Press, 2009). 9. he recent book of Jehanne M. Gheith and R. Katheriene Jolluch, Gulag Voices Oral Histories of Soviet Incarceration and exile (New York : Palgrave, Macmillan, 2011) is a noteworthy exception.

10. See Irena Gruzinska-Gross and Jan T. Gross, eds., War hrough Childern's Eyes: he Soviet Occupation of Poland and the Deportations, 1939-1941 (Stanford : Hoover Institution Press, 1981) Gulag project 13 was based on the hypothesis that there were speciic features in the experience and memory of the Gulag of European deportees compared with those of Soviet citizens. 14 hese features are primarily the experience of having been snatched from one's homeland, caught up in an external policy that destroyed the bonds with one's environment and forms of sociability, and the habitual attitudes towards authority drawn from one's original culture.

From the outset, the project focused on collecting oral testimonies to be archived and presented in a contextualised online museum 15 . he recent date of our survey, when almost all of those deported as adults to the Gulag had died, and the creation of an extensive corpus of oral life-stories 16 meant that childhood and adolescence in the Gulag emerged as one of the central themes of our witnesses' memories.

he corpus of interviews held by the researchers in the "Sound Archives of the Europe of the Gulag" project comprises 170 testimonies collected in the Baltic states, Czech Republic, Germany, Hungary, Kazakhstan, Poland, Romania, Siberia, Slovakia and Ukraine; and also in France, Italy and the United Kingdom, where some of the witnesses settled after their release.

he team of historians, anthropologists, sociologists, demographers and geographers designed an open-ended interview grid with a series of topics to be raised concerning the various stages of the witnesses' lives, before and after arrest, release and 15. For this purpose, sound quality was a priority. he presence of recording equipment and in some cases sound engineers from Radio France Internationale, a project partner, was part of the interview environment and had an inluence and a role the extent of which remains to be analysed.

16. As one wave of European deportations followed another, every social class was afected. Two-thirds of the witnesses were forcibly deported to resettlement villages in Siberia and Kazakhstan, and one-third to labor camps all over the Soviet Union.

key moments of their return and reintegration into their native societies.

he researchers are specialists in the Soviet Union and Central Europe and possess the skills to encompass the great linguistic variety of the region. With witnesses born in countries that were once part of the Soviet Union, it was possible to conduct the interviews either in Russian or the witness's mother tongue.

Wherever possible and agreed, the interviews were held in the witness's home, but also in some cases in the oices of former deportees' associations, synagogues or workplaces that had been the scene of their testimonies.

Each researcher in charge of data collection for a given country had a degree of freedom in deciding how to conduct the interviews, how long they lasted and how direct and persistent the questions were. he corpus therefore contains life stories that last from two to ive hours in varied forms due to socio-cultural diferences between the witnesses and the various priorities of the researchers. he witnesses were all informed in advance that their stories would be preserved in sound archives and uploaded to a virtual museum entitled European memories of the Gulag, and gave their written consent.

his article proposes a few suggestions for approaching the speciic aspects of being a child in the Gulag, memories in later life and the efects of a "deportee" childhood on adult life, particularly the process of turning this experience into a testimony.

A host of deported children

In September 1939, following the German-Soviet non-aggression pact, the USSR annexed the eastern territories of Poland (now part of Ukraine and Belarus), Romania (northern Bukovina and Bessarabia) and all of the Baltic states.

he political, economic and military elites of the various "nationalities" (natsional'nost in Soviet administrative parlance, an ethnic category) in these territories -Poles, Jews, Germans, Ukrainians, Lithuanians, Latvians, Estonians and Belarusians -were forcibly deported or sentenced to hard labour in the camps of the Gulag.

In Poland, in 1940 and 1941, the Soviets held four major waves of deportation, intended to purge its eastern regions of "undesirable" elements.

he irst operation, in February 1940, was aimed mainly at civilian and military settlers, osadniki, army veterans who had fought in the First World War or the Russian-Polish War of 1920, and civilians who had been granted land in the border regions. Some 28,570 families, totalling 140,000 people, were deported to the Russian Far North, Kazakhstan and Siberia.

In April 1940, the groups deported were mainly Polish civil servants -policemen, gendarmes, prison warders, administrative staf -and members of the "property-owning classes" -industrialists, bankers, self-employed, shop-ownerstogether with their families.

In the third wave, in June 1940, the category targeted was the refugees who had led western Poland occupied by the Germans for the eastern regions, but had refused the citizenship ofered them by the occupying Soviet authorities. Of the 76,000 people forcibly deported to Siberian villages, 80% were Jews, who thus ironically escaped massacre and extermination at the hands of the Nazis.

he inal purge, in June 1941, extended beyond the Polish eastern territories to the three Baltic states and Moldova. he aim was to "cleanse" these territories of anti-Soviet and "socially dangerous" elements.

During this operation, the target groups were divided into those who were arrested and sentenced to hard labour, and those who were forcibly deported to the resettlement villages, including large numbers of children he special resettlers, on the other hand, were targeted as social or ethnic groups deemed to be dangerous for Soviet authority. hey were deported collectively as families, by administrative decision, placed under house arrest in resettlement villages, where they built their own huts and worked on farms or forestry sites under the supervision of commandants responsible for their surveillance. Some were employed in new factories. Oicially they continued to enjoy civic rights, but were obliged to do heavy work as directed by the authorities. hey were supposed to receive payment, usually in kind, and were allowed to move freely within the limits of their village, but had to report at least once a month to the oice of the local administration.

In 1943, as the Wehrmacht was driven back and these territories were recovered by the Red Army, the Soviet political police undertook a further wave of purges, arresting and sentencing to hard labour or forcibly deporting hundreds of thousands of individuals and families with children from Estonia, Latvia, Lithuania and western Ukraine.

Baltic farmers' systematic opposition to forced land collectivisation and support for the anti-Soviet resistance hiding in the forests caused the authorities in Moscow to launch a number of operations from 1948 to 1950 to deport some 200,000 farming families together with their children.

Furthermore, arrests were made of those suspected of collaborating with the Nazis, those who had been forced to go and work in Germany or had done so voluntarily, civilian and armed members of the resistance to the Red Army, including many teenagers, and soldiers who had joined the Wehrmacht and SS.

From western Ukraine, for example, the Soviet authorities deported activists and sympathisers of the Organisation of Ukrainian Nationalists (OUN), oicers and men of the Ukrainian Insurgent Army (UPA), collaborators and soldiers of the Galicia Division of Wafen-SS volunteers.

To stop farmers' support for the UPA, the NKVD/ MVD (Soviet political police) burnt entire villages and deported all their residents. he most widespread practice was to accuse young people of belonging to the OUN and sentence them to long periods in Gulag camps, while members of their families were deported and put to work on the kolkhoz farms in Kazakhstan or Siberia.

From 1945 on, many teenagers from the large "ethnic" German minorities in the territories recaptured by the Red Army in Bulgaria, Czechoslovakia, Hungary and Yugoslavia were deported to the USSR.

Similarly, as the Red Army advanced towards Berlin, irst in Hungary and then in Germany the Soviets carried out massive, arbitrary raids to deport hundred of thousands of prisoners, many of them teenagers, to make them "contribute" to the reconstruction of the Soviet Union.

Shattered childhoods

he wide variety of experiences and memories of these years of deportation and exile is due to people's various statuses and the traumas undergone, whether those who were deported as a family, those who were born in exile and those who were deported alone. It is also due to their social and national origins and the signiicance of these origins in the Soviet ideology of the purges during that historical period.

A modest farming background, for example, provided practical resources for the adults and older children to put up with the rough life and conditions of forced labour, while an urban upbringing, despite the greater fragility it involved, sometimes enabled the parents to take on administrative tasks that were less physically harsh.

Learning Russian was decisive for survival and socialisation in the camp hierarchy, and for the children who attended school in the resettlement villages, luent Russian made relations with local people easier.

he extensive purges of many diferent social groups the Soviet regime orchestrated and institutionalised from its earliest days rapidly widened the criteria for "catching" the victims, ignoring social and legal distinctions of age.

Furthermore, during the occupation of the Baltic states and the eastern territories of Poland, deportation and forced removal afected entire families of several generations. In the Axis countries at the end of the War, the supposed collective guilt of the entire population justiied picking up individual children and teenagers, often arrested at random and sentenced to hard labour in the camps of the Gulag for periods of ive to ten years.

Although the purges took little account of age, when the deportees arrived at their destinations, the children's trajectories varied according to whether they were in the camps or the resettlement villages. In the camps, the extremely hard labour united all ages, including teenagers, under the same rules and production norms. However, in the resettlement villages, distinctions re-appeared to some extent as part of a stated aim of re-education, with theoretically compulsory school lessons for those under age, who were not assigned work like the adults. In practice, particularly during the war years, separation from a father interned in a camp, a mother's physical weakness, illness or death, and having younger brothers and sisters in extreme poverty inevitably forced some of them to ensure their survival by joining in adult work.

Separation and loss

Within the corpus of interviewees, the largest group who were children in the Gulag were those deported at a young age with their families from the eastern territories of Poland (now western Ukraine and Belarus), the Baltic states and Moldova before the German invasion of the USSR, western Ukraine and the Baltic states, from 1944 to 1953. Does this corpus of interviews represent all the children of the Gulag?

Among the testimonies, the circumstances of arrest seem to be frozen by the memory of their parents, helpless, humiliated and mistreated. his memory is emotionally the most diicult point for those who have recounted their deportation years after, and the experience appears to be even more violent and devastating than their own humiliation, which is rarely spelt out. he unspoken nature of their own humiliation may be understood to be due either to its inclusion in their parents' sufering by a child's subsequent identiication with them, or to its repression by the "screen memory" (Deckerinnerung) of their parents' humiliation. Many children eventually lost their entire family and, because they were alone, were placed in orphanages in the places of exile. Usually this placement marked the start of a rapid loss of memory of any individual or ethnic identity under the pressure of their fellow orphans and the continual indoctrination in Soviet values by their teachers. While some survived and returned home as a result of the persistence of a family member still living in the home country, others lost all memory of their origins and identity for ever, and their later lives in the USSR were haunted by a desperate and usually unsuccessful search for those origins. 20

Peep Varju was four and a half in 1941, when he was separated from his father, who had been sentenced to hard labour, and deported from Estonia to the Tomsk region in Siberia with his pregnant mother, his brother and sister.

When all his family starved to death, Peep was placed in a Siberian orphanage. Soviet authorities and collected gifts and money to support the men of the Ukrainian Insurgent Army (UPA), who were ighting the Red Army in the Carpathian forests. 24

In December 1949, just 15 years old, he was taken out of class with his friends and arrested. After a long journey through the prisons of the USSR, including the Butyrka in Moscow, he was sentenced to ive years' forced labour for high treason and anti-Soviet conspiracy.

"We were ordered to report to the governor, me and my friend Bogdan, and the political police were there waiting for us. hey took us irst to the Dzerzhinsky prison and then, a few days later, to the Lonsky Street prison. he cell was small with just a tiny window, there were no beds or mattresses, we slept on the loor, covering ourselves with our coats and using our boots as pillows! At night we couldn't sleep, the door was always open and we would be taken away for interrogation. here were a lot of us, 35 or 40 per cell. he day began with prayers, if there was no priest, the cell senior said them; and then there was breakfast, tea and bread, nothing else." 25

Although the feelings of loneliness, abandonment and despair might last long after a child's arrival in the camp, their memories of these years of exile often focus on encounters that created bonds of ainity or friendship that seem to have occupied the empty space left by the loss of a family and given a human meaning to extreme experiences. hey are relived and repeated in recent accounts as the beginnings of a sudden and abrupt maturing process with acts of survival and mutual assistance, each of which is both a source of pride and a resource, that appear in hindsight to have built up the strength the person would need on returning home. his shows in the metaphor of the Gulag as a "school" or "university" that recurs in these accounts.

Klara Hartmann, transferred in 1949 to the Steplag in Kazakhstan, intended solely for "particularly dangerous" prisoners, experienced fellowship and solidarity in a mainly Ukrainian work brigade. 26 he accounts of those who, like Orest-Yuri Yarynich, were arrested and deported with friends speak of their experiences in the plural, constantly using the term "we", transforming their own experience in the camp into a story of ordeals overcome by a sort of band of brothers. Yarynich served his sentence in various sections of the special camp in Mordovia for particularly dangerous prisoners:

"… from the Butyrka prison in Moscow we were taken to the Pot'ma railway halt in Mordovia and then to Camp 5. We were quarantined and during that time we met the Estonians, Latvians and Lithuanians. We were not enemies. On the contrary, they helped us. hey had some dry cheese that helped us cope with the hunger. After quarantine we were allocated to lagpunkt (division) 3 of the Mordovian camp. We were allowed to receive one letter a year and a parcel every three months." 27

Another facet of childhood in the Gulag concerns those children born in exile. Consequently, their earliest experience was not separation and violent arrest or their parents' humiliation and helplessness. heir memories seem to be full of the "naturalness" of an early childhood where life in exile was the norm.

hey grew up in that environment and many went to school there. he teaching they received imbued them with the social, cultural and political values of the Soviet system, and some even had ideas of joining the Communist youth movement or ambitions of living as "Soviet adults".

Nadezhda Tutik was born in Omsk, Siberia, in 1950, where her parents had been deported some years before during land collectivisation in western Ukraine. She spent all her childhood and adolescence there, because her parents were not allowed to return to Lviv until 1969. In her account, she makes the point several times that the fact of being born there determined her perception of Siberia and life in exile. In particular, when she speaks of her membership in the Komsomol (Communist youth movement), she explains the diference between her and her cousin, who had been deported at the age of 10 and had lost a brother during the journey. He "harboured in his soul a feeling of profound humiliation". He never applied to enter the Komsomol, he hated the Soviet authorities and paid heavily for his hostility, because "they stopped him getting on in the world". For her, however, despite her parents' social origin and status as deportees, which were usually a bar to Komsomol membership, joining the movement was "very simple". Everyone voted to admit her: "I' d been born there, I' d grown up with them, we were friends". 28 he accounts often reveal a sort of duplication of these childhood memories by a more recent, critical memory, reconstructed when, as adults, they learnt of the sufering and violence their parents had endured. After reading Jung Chang's Wild Swans, she decided to write the story of her mother's and father's families. hese memoirs, published in 2001 30 , quickly became a major reference for the public narrative memory of the Soviet purges in Latvia. Since then, she has pressed for these purges to be recognised by the European authorities as "genocide".

As the child of a couple deported in the irst and second purges, her political identity gains legitimacy from this cumulative genealogy of Latvian collective sufering, for which she is both a representative and a symbol.

Growing up in exile

In the witnesses' accounts, hard labour, hunger, cold, disease and death are ordeals that rack and often destroy body and soul and often appear as closely overlapping and linked.

he testimonies of children who were born in the Gulag or deported with their families recount these ordeals as overwhelming the entire family, afecting one member after another. However, the accounts of adolescents sentenced to hard labour often describe them as additional to their inconsolable feelings of loss of self, loneliness and isolation. In both cases, these ordeals, whether separate or accumulated, form the backdrop to all the major events of the period of exile. heir overlapping occurrence maintained a constant feeling of fear interspersed by moments of pride when mutual aid, individual strategies or random transfers briely lightened their ever-present weight.

We may suppose that life as a child in the settlement villages and camps was marked by violence between children of diferent origins, and by physical or psychological bullying from adults in authority (political police oicers, investigators, warders, komandants, orphanage staf and school teachers) or prisoners from the criminal underworld in the camps.

Although the approach adopted in our method for collecting testimonies was to allow the witnesses considerable freedom in what they chose to evoke from their personal experiences, the absence or bare mention of this violence sufered is noteworthy and requires greater research. But it also raises the question of repression or the unspoken as a form of language, supplementing the spoken word in narrating traumatic experiences.

Rimgaudas Ruzgys was born in northern Latvia in 1937. His parents were well-to-do farmers.

During land collectivisation in May 1948, the Ruzgys family was arrested and deported to Buryatia in southern Siberia. 31 A few days after arriving, "everyone began work". Rimgaudas's mother was assigned to a brick-works:

"But it was a brick-works in name only. he work was done like in the days of serfdom. he women dug out the clay with their hands, trod it underfoot and moulded the bricks by hand. he weather was already cold and Mother quickly fell ill. Her legs were swollen from treading the cold clay." 32

His father was sent logging. First, they had to build huts for the deportees before the irst snow fell. In the autumn, the family moved to the new village of Moyga, where the deportees built the huts. his irst winter seems to have been the worst:

"In winter, it was -40°C. he hut was built of unseasoned logs, and when it was heated, drops of condensation fell on our heads. here was no sawmill and we made planks by splitting the pine logs with an axe. We built the loor, walls and ceiling with these planks. We covered the ground with soil to keep it warmer. Since the hut had no foundations, we piled up soil against the walls outside, up to the windows. In our room, we built a sort of bunk bed with planks." 33 Adam Chwaliński's mother fell seriously ill after only a few months; Adam, aged eleven and a half, and his sister, fourteen, went with their father, also in poor health but considered it for work, out into the taiga and learnt to cut timber.

"Although my sister was three years older than me, she was afraid of climbing on the tree-trunks, because you had to climb 1.5 or 2 metres above the ground… So I would stand on top, and my sister below, and we 31. http://museum.gulagmemories.eu/en/salle/rimgaudas-ruzgys,Rimgaudas Ruzgys's biography pages (accessed February 7, 2014). Meanwhile, that irst winter Rimgaudas went to a school built by the deportees. here were only four Lithuanian pupils in his class because most of the children went out working to help their families survive. He went straight into the fourth year; learning Russian was a problem for him, but he was good at the exact sciences. He inished the school year at the end of the irst winter with a letter of congratulations, but left school to work. He was only 11. His irst job was marking the cut logs. 35 After three years at Ukhta, Komi Republic, Klara Hartmann was transferred to Kazakhstan, to the building-site for a new concentration complex, the Steplag, one of the ten special camps for "particularly dangerous prisoners" set up after 1948 near existing camps throughout the Soviet Union. Quickly, the warders made them dig the ground for rammed earth to build the camp. he irst large hut, for the women, then the second, for the men, and the separating wall between them were completed before the cold set in. hen they built other huts, the kitchens, baths and latrines, oices and accommodation for warders and camp oicers: 36

"he women worked much longer than the men: we were always the ones who were assigned night work. hen we built the town as well: lats, or rather, rooms in the Russian style for the families of free workers, then the uranium reining plant." 37

Hunger forms the backdrop to all the accounts. Irina Tarnavska weeps as she recalls the everpresent hunger and the diiculties in inding the least edible scrap.

"We would wait for Mother, when she came back from work to eat together. I went to site over the cooking pot and tried to breathe in the smell of the potatoes. hat's how I illed myself ! And when Mother came back from work, we ate the potatoes and that was that. " 38

Peep Varju remembers the extreme poverty of the last days he lived with his family before they died:

"I remember the little khutor (homestead) where we all lived together, we slept on the loor, it was very cramped and very cold and I remember that we were always starving. I can still see my mother taking some belongings with her, going out and when she came back, we could eat something.

In the end we had no clothes left, she had sold them all for food; except for a dressing-gown, I had nothing left to wear." 39

In the places of exile, school and the company of other children sometimes provided brief glimpses of a supericially "normal" childhood and coloured these memories with the accounts of discoveries, games and carefree moments shared among children. Irina Tarnavska remembers:

"here was nowhere to play. In the summer, we were very tired, we didn't feel like playing.

And in winter when we went to school, yes, I used to ski. And later, when we got older, we played. We played tag. I could still remember our Ukrainian games and we played them. We were young, you know, we felt things. When I inished 7th class, we went dancing. hey'd built a clubhouse and someone would play the accordion. So they held dances, sometimes there were ilms, there was a choir at school. I've even got a photo of it! " helps people survive. I can tell you that the Lithuanians saved a generation of Latvians with their love for music, they did!" 42

In Irina Tarnavska's account, as in many others, the memories of hunger and cold are accompanied by the wonderment they felt at the summer abundance of the Siberian forests, which appeared both beautiful and nurturing.

In this way the image of Siberia in these later accounts combines the fear of life near wolves and bears, the experience of a frozen, deadly wilderness and that of an abundance of resources during the few summer months, all the more salient because of the contrast with the abject poverty of the human beings.

"In Siberia, there are lots of mushrooms and berries. Our parents didn't have time, but we children used to go into the forest to pick berries and mushrooms. hat's how we survived. We were so hungry, so thin, all of us.

We would look for bilberries; we were so hungry for anything sweet! here were all sorts, raspberries, lingonberries, bilberries and then, just before winter set in, we would go cranberry-picking in the marshes, and when the irst cold arrives, the cranberries turn bright red, it was so beautiful!" 43

Returning from exile

he return from exile for the children of European parents occurred in various ways and at various times between the death of Stalin in 1953 and 1960. Whereas for the camp prisoners, sentenced to long years of hard labour, release involved a legal and administrative process concerning each one individually, the special resettlers were released by decrees afecting large categories of people who were no longer required to report regularly to the local authorities.

Some children returned with their parents, others, orphaned or sent ahead by the adults to prepare their own return, had to be taken in by family members back in the home country. Some returned alone and found nobody.

For many young men, release meant immediate call-up into the army. Military service was often experienced as a "second deportation", 44 but also as a harsh period, easier to bear because of acquired survival skills, when it was often possible to gain promotion to protected positions. 45 For the others, their experience of the return was shaped by discoveries that overturned their world of certainties. First, the journey back, sometimes lasting weeks, this time in carriages with windows, revealed a Soviet Union perceived as povertystricken and chaotic. hen came the shock of their irst sight of their home country: "Suddenly, in Tallinn, I saw another world, sophisticated, civilised, with properly dressed people talking quietly and politely to each other." 46

But the administrative reality of these Sovietised countries soon broke through, sending the young people back and forth between short-term accommodation and employment, with many a pitfall in getting their papers in order.

"When I arrived in Lvov in 1964, the militia would not issue me with a propiska (required residency permit) because I was considered to be a banderovka 47 returning from exile. hey said that if I found a job they would give me the propiska, but in the workplaces they said: when you get the propiska, we'll give you a job. I spent three months sleeping at the railway station and going back and forth between the militia oices and the workplace." 48

Over the months, the silence imposed on them about their past experience, their uncertainty and loneliness ironically revealed to some their attachment to life in Siberia and the community of deportees.

In 1947, Silva Linarte, having lost her father, beneited from a decision to allow her to return to Latvia after ive years of exile. hese ambivalent feelings that were hard to share with friends and family were based on the contrast between the images of the homeland handed down by deportee parents and the reality they found on their return. When she irst got of the train, Nadezhda Tutik asked her mother in surprise, "Is this Ukraine?" "It looked just the same (as Siberia)… I didn't understand why they were so proud of this Ukraine!"

In addition, unlike those sentenced to the camps, the young deportees had all spent time in institutions where they were socialised and often educated. he children of the families resettled in villages could only be taught in boarding schools, while those in large and small towns attended day schools. hose with no parents were placed in orphanages. hey all received a strict Soviet-style education, but the boarding schools and orphanages imposed a greater interiorisation of Soviet values and norms. his "Sovietisation" caused diiculties when they returned to their families and gave rise to biased views of their parents' lives and responsibilities. Some saw their father, serving a camp sentence, as a heroic ighter in the Great Patriotic War.

Some conclusions

he most striking feature of the deportee childhoods recalled in these later accounts is their great variety, making it diicult to construct a typology. However, some common points do emerge. First, the experience of a sharp break, expressed in the memory of the extreme brutality and suddenness of the mass arrests. In just a few hours, these destroyed the domestic world of socialisation and family authority that structured their lives and forced the children to instantly adopt new rules and survival techniques for the successive blows of family breakup, death of some family members and continual threat for the others.

he second point these testimonies have in common is the memory of attempts at retrieving and internally reconstructing these family bonds, which are seen as protective walls against the feeling of loss of identity under the continual threat of family destruction. hese took the form of taking on responsibility for loved ones' survival, leading to a premature and rapid gain in maturity.

In the later accounts, the often minutely detailed recall of family relationships seems to have the function of reairming genealogical bonds and their continuity torn asunder by the Soviet system. Return and reintegration are recalled as a series of new breaks with the social routine of exile, the ixed, idealised image of the homeland handed down by parents and hopes for a welcoming reception. his made the longed-for return painful and lonely. At the same time, the experience of forms of indiference and rejection they had not known before seems to have caused an emotional re-assessment of Siberia and deportee society where everyone bore the same stigma. his repositioning of the experience of deportation is one of the major characteristics in these later accounts 52 .

hese accounts also involve speciic forms of memory reconstruction. Many recall a later point in time when, as adults, the witnesses realised the extent of their parents' sufering and humiliation and often discovered for the irst time how they had died in exile.

his realisation overlays on their childhood memories a second, proxy, memory, on behalf of the older generation, creating a sort of "memory duplication". his divergence between a child's 52. his is one of the topics in the book the authors are writing on childhood in the Gulag.

memory focusing on positive and negative details of daily life and the later realisation of the ordeals sufered by their parents lends these accounts a certain emotional ambiguity and feelings of guilt.

Another feature of the childhood experience of deportation appears to be the burden of exile for subsequent relations with parents, whether living or dead. his shows in an intense attachment even as far as identifying with them in recalling memories, an attachment aroused by their sufering and the need to protect them and their memory. hese feelings may be accompanied by those of a life-long indebtedness, as if the parents' suffering had been the price of their own survival.

here remains to examine any bias to the accounts caused by the manner in which they were produced, with the technical recording of the testimonies as required for long-term archiving, the focusing of the interview on experience in the Gulag and the "Western" identity of the interviewers.

Most of these accounts emerged in new nations after a long period of latency and suppression due to the regime of silence and secrecy imposed by the Communist system, which prevented the emergence of any public narrative discourse concerning the deportations. Once the Communist regimes collapsed, this hibernation of collective public memory was followed by an urgent social need for written and oral evidence of Soviet repression to underpin the political legitimacy of new democratic stakeholders and institutions. he national collective narrative that emerged now includes socially legitimate elements of discourse for constructing individual and family narratives, making witnesses of the "rememberers".

he procedures of our survey most probably reactivated this process among our respondents. he prospect of having their stories broadcast outside their national borders appears to meet the feelings of a debt of memory towards the dead that underlie all the accounts.

Although some of the accounts used expressions taken from the national public discourse on the Gulag, the existential intensity of the experience appears to have gone beyond that to a personal language charged with images that recall childhood. hat these stories were recounted at a later period perhaps provided an emotional ilter: far from expressing hatred or resentment, these former child deportees recalled their experience in a nuanced way with more than one interpretation.

  ; Cathy A. Frierson and Semyon S. Vilensky, Children of the Gulag (New Haven and London : Yale University Press, 2010). 11. See «Surtout les enfants... «, Bensoussan Georges ed., Le Monde Juif/Revue d'Histoire de la Shoah n°155, CDJC, 1995, 265 ; and the more general L' enfant et le génocide, Catherine Coquio and Aurélia Kalinsky ed. (Paris : Robert Lafont, 2007) with its impressive bibliography. 12. he essential elements in oral history methodology for Growing up in the Gulag: later accounts of deportation to the USSR 5/18 Fondation Maison des sciences de l'homme -190 avenue de France -75013 Paris -France http://www.fmsh.fr -FMSH-WP-2014-62

  32. Jurgita Mačiulitė, « Une âme de paysan », in Alain Blum, MartaCraveri and Valérie Nivelon, 258-9. 33. Ibid. Growing up in the Gulag: later accounts of deportation to the USSR 12/18 Fondation Maison des sciences de l'homme -190 avenue de France -75013 Paris -France http://www.fmsh.fr -FMSH-WP-2014-62 would work the saw. And just before we sawed it through, it would crack and the whole lot would fall into the mud. It was dangerous: if I'd been thrown down and buried under the pile, I couldn't have got out again." 34

  Mother opened the door. Armed men, soldiers, came in and said to Mother, "Get ready, we're taking you where the polar bears live!" mother, and she may die, too, at any moment. She's almost unconscious.' I took her by the hand and we went to the hospital… When I got back to town, my father was waiting for me on his own. In despair, he said to me, 'You know what, Mother has already been buried in a hurry, wrapped in a blanket, somewhere down by the river.' He didn't even show the place and said I had to go there. He' d already found out where we had to report… We went to the other end of the town and suddenly my father stopped as if he' d walked into a wall, and began to be delirious. After crossing the icy river, he had caught pneumonia and was feverish. I shook him and he said, 'Remember. I'm going to die any time now. Remember, you must bury me in a cemetery.'" 19

	Mother began crying and did not get ready.
	She had long braids. He caught Mother by
	the hair and pulled her. Mother fell down and
	he dragged her to the sledge. here was a lot of
	snow, probably more than 50 centimetres. So
	they dragged us away with Mother, we were
	aged 10, 7 and the youngest 5, and we got our-
	selves ready." 17
	he children were deported either with both
	parents, brothers and sisters or, sometimes, as in
	Poland, with their grandparents and other mem-
	bers of the family. Where the father was sen-
	tenced to labour camp, they were deported wit-
	Adam Chwaliński was born in Polesia (now in
	Belarus) in 1928, to a Polish family of civilian sett-
	lers. On 10 February 1940, his family was arrested
	by the NKVD and deported along with the other
	51 families from his native village. After travel-
	ling for a month, they arrived in the Arkhangelsk
	region. In November 1941 18 they travelled on to
	Central Asia. In Kyrgyzstan, Adam heard that his
	mother had suddenly died:
	"I arrived and saw an incredible sight. My
	little sister was standing there in the middle of
	the street with her arms stretched out. She was
	screaming and crying. She must have realised
	that Mother was dead. And I was incapable
	of crying or speaking. My father wasn't there;
	he'd gone to take my elder brother to the hos-pital. People said to me, ' Adam, take your sister to the hospital, she's standing there, near her	Irina Tarnavska was born in Lviv in 1940, in what was by then Soviet western Ukraine. Her far-mer parents were forcibly deported to the Tomsk
	17. Archives sonores Mémoires européennes du Goulag, Paris, CERCEC/RFI, interview with Irina Tarnavska, Lviv, 21	region in Siberia during collectivisation in 1948. Recalling the point at which her family's life col-
	October 2009.	lapsed, she had a it of sobs that continued throu-
		ghout her account:

"Someone knocked at the door. Mother asked, "Who's there?" hey said, "Open up! We're friends." hout him. he absence of the father or the death of the mother from hunger, cold or over-work often meant that the oldest child was forced to be the "head of the family". his was both an additional trauma and the sudden emergence of an adult identity, which seems strangely to have forged an attachment for life to the mother, dead or surviving, as if the child took not only her place but also a part of her identity.

18. Following the July 1941 agreement in London between the Polish government-in-exile and the Soviet Union and the August 1941 "amnesty to all Polish citizens now detained on Soviet territory either as prisoners of war or on other suicient grounds". dead

  "I managed to escape, because when the ice on the Ob began to melt in the spring, other deportees took me and other orphans by boat to the orphanage. When I entered the orphanage, I only spoke Estonian.Because we were not allowed to speak Estonian, I quickly forgot my mother tongue. here's a scene I remember, one day I went up to this little Estonian girl, opened my mouth and could not get a word of Estonian out. In the orphanage, I fell ill, there was a typhoid epidemic and I nearly died too."21 In Germany, Hungary, Romania and Slovakia, enemy countries for the USSR from 1941, children and teenagers were arrested and sentenced to hard labour either after arbitrary raids or because of their family or ethnic origins or membership (sometimes under compulsion) of youth organisations that gave military training 22 . In the Baltic states and western Ukraine, most of the young people sentenced to hard labour were civilian and armed members of the resistance. he recurring theme in the later accounts of these girls and boys is a feeling of brutal and irrevocable separation from their familiar world, of deep loneliness and isolation, accompanied by shock at the violence of what was happening to them, particularly for those picked up at random.

	Growing up in the Gulag: later accounts of deportation to the USSR	9/18
	Klara Hartmann was born in May 1930 in Mis-
	kolc in northern Hungary. Her parents were far-
	mers who died young and she does not remember
	them. She was brought up by an uncle, a gen-
	darmerie sergeant at Gönc. As the Red Army
	advanced in January 1945, her uncle and aunt
	led, leaving her alone.
	Aged 14, she was arrested, interrogated and tor-
	tured for almost a year in prison in Kiev, then
	sentenced to ten years' hard labour for spying for
	the Germans. At Vorkuta, she worked on buil-
	ding sites. Bullied by the Soviet women impri-
	soned for criminal ofences, only reluctantly lear-
	ning Russian, she was totally isolated, with no
	other Hungarian in the camp. 23
	Orest-Yuri Yarynich was born in October 1934 in
	Lviv in western Ukraine, then in Poland. At the
	end of the War, barely a teenager, he formed an
	underground group with his school friends; they
	handed out tracts calling for civil resistance to the	It was an orphanage for pre-school children;
		those who attended school were in another
	21. Archives sonores Mémoires européennes du Goulag, Paris,	orphanage.	,
	CERCEC/RFI, interview with, Peep Varju, Tallin, 19 Ja-
	nuary 2009.

19. Testimony of Adam Chwaliński, cf. Agnieszka Niewiedzial, "Se battre et combattre ", in Alain Blum, Marta Craveri and Valérie Nivelon, 91-2. 20. Cf. Madina Vérillons Djoussoeva, Guillaume Vincent and Les enfants du Goulag, Film, Directed by Romain Icard, (Paris :Production Utopic, Les Films en Vrac, 2011). Fondation Maison des sciences de l'homme -190 avenue de France -75013 Paris -France http://www.fmsh.fr -FMSH-WP-2014-62 22. Such as the Hitler Youth in Germany and Levente in Hungary. 23. Cf. http://museum.gulagmemories.eu/en/salle/klarahartmann, Klara Hartmann's biography pages (accessed February 7, 2014).

  I don't know why Siberia is now seen as the deportees' place of sufering. It's the most beautiful place in the world! Everything grows there, wonderful lowers, berries of all kinds. hey have turned it into a place of exile, of sufering for peoples, when they should have made it an international holiday centre!" 49

	Growing up in the Gulag: later accounts of deportation to the USSR	14/18
	But she was depor-
	ted again with her mother and sisters in 1950.
	Despite a childhood marked by her father's death
	in the Viatlag camp and two deportations, she
	recalls Siberia in these terms:
	44. Jurgita Mačiulitė, 265.
	45. Rimgaudas Ruzgys, for example, with the driving licence
	he passed in exile, became the general's personal chaufeur.

46. Archives sonores Mémoires européennes du

Goulag, Paris, CERCEC/RFI, interview with, Peep Varju. 47. Supporters of Stepan Bandera, head of the Organisation of Ukrainian Nationalists (OUN). 48. Archives sonores Mémoires européennes du Goulag, Paris, CERCEC/RFI, interview with Irina Tarnavska. Fondation Maison des sciences de l'homme -190 avenue de France -75013 Paris -France http://www.fmsh.fr -FMSH-WP-2014-62 "

Cet article constitue une contribution à la connaissance d'un pan très peu étudié de l'histoire du goulag, celle des enfants déportés des pays d'Europe centrale et orientale avant et après la Seconde Guerre mondiale. Il propose quelques jalons pour une approche de la spéciicité de l' expérience infantile en déportation, de la diversité de sa remémoration tardive. Il interroge les formes spéciiques de cette remémoration et mise en récit de l' enfance au goulag et l' empreinte de ces enfances « déplacées » dans la vie adulte, notamment à travers le processus de transformation de cette expérience en témoignage. La recherche est fondée sur le corpus de témoignages oraux recueillis, notamment par les auteurs, dans le cadre du projet Mémoires européennes du Goulag dans les pays de l'Europe centrale et orientale.

Fondation Maison des sciences de l'homme -190 avenue de France -75013 Paris -France http://www.fmsh.fr -FMSH-WP-2014-62

http://www.fmsh.fr http://halshs.archives-ouvertes.fr/FMSH-WP http://wpfmsh.hypotheses.org ://www.fmsh.fr -FMSH


Jean-Sébastien Bernier

Roberta Citro

Corinna Kollath

Edmond Orignac

Correlation dynamics during a slow interaction quench in a one-dimensional Bose gas

Keywords: numbers: 67.85.-d, 03.75.Kk, 03.75.Lm, 67.25.D-

We investigate the response of a one-dimensional Bose gas to a slow increase of its interaction strength. We focus on the rich dynamics of equal-time single-particle correlations treating the Lieb-Liniger model within a bosonization approach and the Bose-Hubbard model using the time-dependent density-matrix renormalization group method. For short distances, correlations follow a power-law with distance with an exponent given by the adiabatic approximation. In contrast, for long distances, correlations decay algebraically with an exponent understood within the sudden quench approximation. This long distance regime is separated from an intermediate distance one by a generalized Lieb-Robinson criterion. At long times, in this intermediate regime, bosonization predicts that single-particle correlations decay following a stretched exponential. This latter regime is unconventional as, for one-dimensional interacting systems, the decay of single-particle correlations is usually algebraic within the Luttinger liquid picture. We develop here an intuitive understanding for the propagation of correlations, in terms of a generalized light-cone, applicable to a large variety of systems and quench forms.

Introduction: Recent advances in the development of fast probing and control techniques applicable to correlated systems have opened up the possibility to dynamically prepare complex quantum many-body states. For example, effective phase transitions have been induced through the application of external driving fields [START_REF] Lignier | [END_REF][2][3] and states, such as a Bell state of ions or a Tonks-like state in a quantum gas, have been realized using tailored environments [4,5]. In fact, the dynamical preparation of states promises to have an important impact in fields as diverse as condensed matter physics, quantum information, quantum optics and ultracold atomic physics. On the theoretical side, despite tremendous progress in recent years, many of the basic concepts behind the dynamical generation of states still remain to be understood.

In this article, we focus on the preparation of unconventional states in isolated systems using slow parameter changes. Considerable experimental efforts have been devoted to understand slow quench dynamics [6][7][8][9][10]. However, in these works, as well as in many theoretical ones (see Ref. 11 and references therein), the emphasis has been put on understanding how energy is absorbed and defects produced.

In recent years, the focus has partially shifted towards the study of longer range correlation dynamics during a slow parameter quench [12][13][14][15][16][17][18][19][20][21][22]. Understanding the evolution of such correlations is paramount as the nature of many-body quantum states are typically characterized by longer range correlators. Interestingly, light-cone-like spreading [23,24] of parity correlations, both in space and time, has even been observed experimentally in an interacting one-dimensional bosonic gas after a sudden quench of the optical lattice depth [25]. For slow quenches, a similar linear light-cone-like evolution of correlations has been predicted for density correlations in bosonic systems [20] and for single-particle correlations in fermionic systems [19].

We analyze here the correlation dynamics during a slow linear increase of the interaction strength, at zero temperature, in two paradigmatic one-dimensional interacting models: the Lieb-Liniger and Bose-Hubbard models. We show that a generalized Lieb-Robinson bound describes the evolution of single-particle correlations. This bound can be understood within a simple picture involving quasiparticle pairs created during the quench. At each instant in time, the quasiparticles propagate at their instantaneous velocity: as this velocity is time-dependent the evolution front possesses a non-trivial functional form. This non-trivial form contrasts with the linear evolution front of correlations, the horizon, which arises after a sudden quench and is due to a constant quasiparticle velocity [24]. The structure of the correlation front can be extracted solely from the knowledge of the quasiparticle velocity and does not require a detailed understanding of the more complicated correlation function. In fact, the approach developed here can be applied to various interacting systems.

For the one-dimensional models under study in this article, we find that outside the bound the single-particle correlations decay algebraically with distance with an exponent determined by the initial Luttinger parameter and decreased amplitude. In contrast, inside the bound, the correlations present much more interesting dynamics. For short distances, the algebraic decay depends on the ramp time [16,19]. While for larger distances and quench times, the correlations, within the Lieb-Liniger model, decay following a stretched exponential. This particular decay form is unexpected as, even for instantaneous quenches, an algebraic decay persists at all distances and times [26]. A similar stretched exponential behavior was found in Ref. 16 (without a time-dependent prefactor). In the rest of the article, we analyze in detail the evolution of singleparticle correlations, and highlight the different regimes both in position and momentum space.

Model: Bosonic atoms in a one-dimensional wave guide can be described by the Lieb-Liniger (LL) model

H = dx - 2 2m ψ † (x)∂ 2 x ψ(x) + g(t) 2 ρ(x) 2 (1)
with ψ(x) the boson annihilation operator and ρ = ψ(x) † ψ(x) the density. The interaction strength g is related to the s-wave scattering length a s of the atoms and to the transverse trapping frequency ω ⊥ by g ≈ 2π ω ⊥ a s . We assume that the gas is initially prepared at a certain interaction strength g(t) = g 0 and that for t > 0 a linear variation of the interaction strength of the form g(t) = g 0 + (g f -g 0 ) t t f is performed. Experimentally this variation can be achieved, for example, by using a Feshbach resonance or by varying the intensity of the transverse trapping [27].

A similar interaction quench can be done by confining bosonic atoms to an optical lattice potential along the onedimensional direction. The theoretical model describing this situation is the Bose-Hubbard model given by

H = -J l b † l+1 b l + h.c. + U (t) 2 l nl (n l -1)
with b † l the operator creating a boson at site l and nl = b † l b l the local density operator. The first term of the Hamiltonian corresponds to the kinetic energy of atoms with hopping amplitude J while the second term is the potential energy with onsite interaction of strength U . Taking the continuum limit of the Bose-Hubbard model in the superfluid phase, this model can be mapped onto the LL Hamiltonian [28]. In this case, the linear interaction quench g(t) translates into a linear change of the interaction amplitude U (t).

For both models, in the superfluid phase, the low energy physics is well described by the Tomonaga-Luttinger liquid (TLL) Hamiltonian [START_REF] Giamarchi | Quantum Physics in One Dimension[END_REF][START_REF] Cazalilla | [END_REF]

H = q q 2 2π u(t)K(t)θ(q)θ(-q) + u(t) K(t) φ(q)φ(-q) (2)
where φ(x) = 1 √ L q φ(q)e iqx e -|q|α/2 and θ(x) = 1 √ L q θ(q)e iqx e -|q|α/2 are conjugate fields satisfying the canonical commutation relation [φ(x), ∇θ(x ′ )] = iπδ(xx ′ ). We have set here = 1 and α is a short distance cutoff. The sound velocity u and the Luttinger parameter K are related to the parameters of the original Hamiltonians. These parameters can, for example, be extracted from the Bethe Ansatz solution of Eq. ( 1) [31] or through numerical approaches for the Bose-Hubbard Hamiltonian [28,32].

In the LL model, the Galilean invariance ensures that the product u(t)K(t) remains unchanged upon varying the interaction parameters [33] and thus u(t)K(t) = u 0 K 0 . For small linear changes of these parameters, this translates, to first order in the variation, to a time-dependent ratio u(t)

K(t) ≈ u0 K0 (1 + t t0 ) with t 0 = πu0t f K0(g f -g0
) and a typical lengthscale l 0 = u 0 t 0 . This result is then used to obtain expressions for the timedependent sound velocity u(t) ≈ u 0 1 + t t0 and for the time-dependent Luttinger parameter K(t) ≈ K 0 / 1 + t t0 . These expressions are still valid for small parameter variations in the Bose-Hubbard model given the relation U 0/f a = g 0/f where a the lattice constant.

A major distinctive feature of the TLL model is that its low energy excitations are collective modes (density fluctuations) instead of individual quasiparticles. Hence, only quasi-long range order persists even down to zero temperature. This situation is exemplified by the anomalous (non-integer) powerlaw dependence of its correlation functions [START_REF] Giamarchi | Quantum Physics in One Dimension[END_REF]. Moreover, the time-dependence does not introduce couplings between the different momentum modes of the TLL Hamiltonian. This leads to momentum decoupled equations of motion for the Fourier components of the fields of the form [16,19,20]

d dt φ(q) = u 0 K 0 q θ(q) and d dt θ(q) = - u(t) K(t) q φ(q). (3)
The solutions for these equations of motion can be written using bosonic quasiparticles with creation and annihilation operators a † and a which diagonalize the Hamiltonian at t = 0:

φ(q, t) = 2 πK 0 |q| a q F * + a † -q F , (4)
θ(q, t) = 1 u(t)K(t)q πK 0 2|q| a q d dt F * + a † -q d dt F (5)
where F (q, t) is the solution of the equation

1 u 0 K 0 d 2 dt 2 F (q, t) = - u(t) K(t) q 2 F (q, t)
with initial conditions F (q, 0) = 1, d dt F (q, t)| t=0 = iu 0 |q|. This solution can be expressed in terms of Bessel functions (see Eq. (9.1.51) of Ref. 34):

F (q, t) = sτ 3 2 √ 3 J 2 3 (s) J 1 3 (sτ 3 2 ) + J -2 3 (s) J -1 3 (sτ 3 2 ) (6) +i J -1 3 (s) J 1 3 (sτ 3 2 ) -J 1 3 (s) J -1 3 (sτ 3 2 )
where s(q, t 0 ) = 2 3 l 0 |q| and τ (t, t 0 ) = 1 + t t0 are the dimensionless momentum and time, respectively [START_REF] Equivalently | the solution can be expressed using Airy functions, but the Bessel function representation leads to a more straightforward derivation of asymptotics[END_REF].

Evolution of the single-particle correlation function: In the following, we survey the rich behavior of the equal-time single-particle correlation function G(x, t) = 1 2 ψ(x, t)ψ † (0, t) + h.c. during a slow interaction quench.

In the bosonization representation, the equal-time singleparticle correlation function takes the form

G(x, t) q≃0 = A 2 0 e iθ(x,t) e -iθ(0,t) = A 2 0 e -1 2 I(ξ,τ, α) (7)
where A 0 is a non-universal constant which depends on the underlying microscopic model. We introduced for convenience the dimensionless length ξ = 3x 2l0 and, correspondingly, the dimensionless short distance cut-off α = 3α 2l0 . The function I(ξ, τ, α) of Eq. ( 7) is then given by

I(ξ, τ, α) = π 2 τ 2 3K 0 ∞ 0 ds s e -αs (1 -cos sξ) (8)
× J 2 3 (s)J -2 3 (sτ 3 2 ) -J -2 3 (s)J 2 3 (sτ 3 2 ) 2 + J -1 3 (s)J -2 3 (sτ 3 2 ) + J 1 3 (s)J 2 3 (sτ 3 2 ) 2 .
From the equation above it immediately follows that Eq. ( 7) only depends on the dimensionless variables τ , ξ, α and not separately on t, t 0 , x and α. This implies that, for a given final value of the interaction strength, increasing the ramp velocity, 1 t0 , mainly enters the expressions through an increased rescaled length ξ.

Asymptotic expansion of the single-particle correlation function:

The time evolution of single-particle correlations described by Eqs. ( 7) and ( 8) is extremely rich. Typical time evolutions of these correlations with distance are shown in panel (a) of Fig. 1 for both the Bose-Hubbard model and the bosonization approach. For the chosen parameters, we found very good agreement between the two evolutions at longer distances, as long as an additional time-dependent prefactor is multiplied to the expression obtained using bosonization. This prefactor corrects for the short distance behavior which is not properly taken into account by the low energy theory. As expected, the bosonization description works best for slow and small parameter changes. In particular, deviations are observed when the Mott-insulating phase of the Bose-Hubbard model is approached or when too many excitations are created.

Initially, before the slow quench begins (at τ = 1 within our formalism), the correlation function decays algebraically with distance as G(ξ) = A 2 0 (1 + (ξ/α) 2 ) -1/(4K0) . This behavior is typical of a Luttinger liquid. Then, as the interaction strength is slowly ramped up, the form of the correlation function evolves. For small ξ and sufficiently short τ , changes are minimal as the correlation function still decays algebraically, but the exponent is now determined by the timedependent Luttinger parameter K(t) = K 0 / √ τ showing up in the exponent [START_REF] Bernier | Supplementary material for Correlation dynamics during a slow interaction quench in a one-dimensional Bose gas[END_REF]. This result implies that for short dimensionless distances, ξ a := τ -1/4 ≫ ξ, the correlations react instantaneously to the slow interaction change and adjust to the ground state decay corresponding to the current interaction value (see panel (a) of Fig. 1). The main contribution to this mechanism comes from quasiparticles with large momenta q ≫ 1 l0 . This adiabatic regime spatially decreases with time and disappears completely when ξ a (t) ≈ α, where α is the dimensionless short distance cut-off.

For larger distances, the correlations deviate much more from their standard initial form and a dip appears. The formation of this dip is a clear signal of the non-equilibrium nature of the physics at play. For distances beyond this dip, the initial algebraic decay, ξ -1/(2K0) , reappears as one can see in panel (a) of Fig. 1. The position of the dip coincides approximately with the correlation evolution front. The time-dependent position of this front can be understood by considering the propagation of quasiparticles. At any given time t, the system Hamiltonian is diagonal in its instantaneous quasiparticles as H(t ′ ) = q u(t ′ )|q|a † q (t ′ )a q (t ′ ) + 1 2 . Assuming discrete time steps, this means that the action of the Hamiltonian at time t -δt, diagonal in its own quasiparticles, has created (and annihilated) entangled quasiparticle pairs a † q (t)a † -q (t). These entangled quasiparticles, forming a pair, propagate with velocity u(t) in opposite direction and thereby carry correlations over a distance 2 u(t) dt within a time interval dt. Hence, for points separated by a distance ξ larger than ξ B = 3 l0 t 0 dt ′ u(t ′ ), the single-particle correlation decay is unaffected by the change in the interaction aside from an overall prefactor. For the system under study, u(t) = u 0 1 + t t0 and we find that ξ B = 2 (τ 3/2 -1). Thus, the evolution front beyond which correlations still follow the initial algebraic decay is given by ξ B as evidenced in Fig. 1. In particular, the position of the bound does not depend on the ramp velocity and time separately as can be seen in panel (b) of Fig 1 . One clearly sees from there that, for a given τ , the position ξ of the dip (measured in units of l 0 ) is the same for different ramp times. The existence of such a propagation front is reminiscent of the light-cone-like evolution of correlations recently investigated in the context of instantaneous quenches [23][24][25][START_REF] Bravyi | [END_REF][38][39].

FIG. 2: Behavior of single-particle correlations with increasing distance for large values of τ /K 2 0 . Exact evaluation of the bosonization expression, Eq. ( 8) -solid lines, is compared to the full approximate expression, Eq. ( 9) -dashed lines. For τ /K 2 0 = 100, we also compare the exact expression to the first exponential term of Eq. ( 9). In the large τ limit, if one adjusts the prefactor correctly, the stretched exponential provides a good description of the correlation decay before ξB. The black dashed line indicates the position of the evolution front ξB = 2 (τ 3/2 -1). Used parameters: smin = 10 -5 , smax = 60 (the lower and upper cut-offs in Eq. ( 8)) and α = 0.1.

For larger dimensionless times, as illustrated in Fig. 2, an additional decay regime takes place at intermediate distances before the bound ξ B . This interesting behavior shows up in the bosonization approach and takes the form

G(ξ, τ ) q≃0 ≃ C(τ ) × (9)
exp -2

1 3 π 2 τ 1 2 K 0 Γ( 1 3 ) 3 ξ 1 3 exp π 3 2 τ 1 2 Γ( 1 6 ) 6K 0 Γ( 1 3 )Γ( 2 3 ) 2 1 ξ 1 3
with C(τ ) a prefactor independent of ξ. For intermediate τ , both exponential terms are required to adequately reproduce the behavior of Eq. ( 8) as shown in Fig. 2. However, for values of τ whose corresponding bound ξ B is located at sufficient large ξ, only the first exponential term is important. In this case single-particle correlations decay with distance as a stretched exponential, a similar decay was found in Ref. 16. Such a functional form is unconventional for Luttinger liquids as, typically, correlations decay algebraically in these systems.

Even for sudden interaction quenches in both bosonic and fermionic systems [26,40] and for slow quenches in fermionic systems [19], only algebraic decay of correlations have been uncovered. The presence of such an unusual functional form is mainly due to the reinforcement of the amplitude of phase fluctuations at low momenta with respect to the equilibrium case. The quench generates an unusual (non-thermal) distribution of quasiparticles around 3 2ξB l0 < q ≤ 1 l0 [START_REF] Bernier | Supplementary material for Correlation dynamics during a slow interaction quench in a one-dimensional Bose gas[END_REF]. Moreover, as the appearance of the stretched exponential decay is limited to large values of τ , this regime only oc-curs for relatively large parameter changes t ≫ t 0 . It is still an open question, whether this stretched exponential decay regime arises within the Bose-Hubbard model. As this regime only occurs for large parameter changes, the TLL model might not describe properly the dynamics of the Bose-Hubbard model and relaxation mechanisms not present in the TLL model might dominate the evolution. A careful analysis of this last point would be extremely valuable but is left to further studies.

Experimental implementation and detection: Onedimensional interacting bosonic gases have been realized experimentally using various setups [41][42][43]. The timedependence of the ratio of potential to kinetic energy can be implemented using Fesbach resonances, or by varying the optical lattice depth or the transverse trapping.

Detection of the single-particle correlation function can also be carried out experimentally. Using radio-frequency pulses, atoms can be outcoupled from the one-dimensional Bose gas at two spatially separated positions and their interference is then observed after a free fall. This technique was successfully employed to measure the build-up of equaltime single-particle correlations in a Bose-Einstein condensate after a sudden decrease of its temperature [44,45]. Another possible detection scheme relies on time-of-flight (TOF) measurements which provide, in the far-field limit, access to the momentum distribution n(q) = dx e iqx G(x). The very long distance behavior of the single-particle correlation is dominated by the Luttinger liquid power-law; however, at a critical wavevector, q c , determined by the ballistic expansion condition, a crossover occurs and n(q) is dominated by the Fourier transform of the stretched exponential. Therefore, at q c ∼ m B ξ B l 0 /t (with m B the atom mass) a crossover should be visible in the TOF measurements. One of the main challenges towards the observation of the evolution of correlations will be the realization of a relatively homogeneous gas as inhomogeneities can cause mass transport and mask the internal evolution [22,46]. The recent experimental realization of a boxed Bose-Einstein condensate [47] offers a possible path towards the realization of the Lieb-Liniger model.

Conclusion:

We uncovered various interesting regimes in the dynamics of single-particle correlations arising during the slow interaction quench of a one-dimensional Bose gas. We proposed a generalized picture for the propagation of the correlation evolution front based on the counterpropagation of entangled quasiparticle pairs moving at each point of time at their instanteneous velocity. Therefore, the evolution front does not simply spread as a light-cone as found following a sudden parameter change [26,48], but aquires a more complex functional form. We expect this picture to apply to other models and quench forms as the evolution front can be predicted from the sole knowledge of the quasiparticle velocity. For example, we expect that for of a linear decrease of the interaction strength U (t) = U 0 (1 -t t0 ), starting from a Mott-insulator, the propagation front will be of the form 4J(2n + 1) t 1 -8n(n+1)J 2 (2n+1) 2 U 2 0 (1-t/t0) as

FIG. 1 :

 1 FIG. 1: Decay of single-particle correlations with increasing distance for different τ and t f . Comparison between results obtained using bosonization Eq. (7) with Luttinger liquid parameters K0 = 4.1561 and u0 = 1.3323 (solid lines) and using timedependent density-matrix renormalization group (t-DMRG) for the Bose-Hubbard model (circles) for a quench from U0 = J (lattice length: L = 100, filling: n = 1, maximum number of bosons per site: 6). (a) Time evolution for different values of τ and for a fixed value of t f = 40 J . The two dashed lines intersecting all τ data sets are the bounds: (left) ξa = τ -1/4 and (right) ξB = 2(τ 3/2 -1). The colored dashed lines on the left of ξB are curves proportional to the function (1 + ( ξ α ) 2 ) -1/(4K(τ )) ; while the dashed lines on the right of ξB are curves proportional to the function ξ -1/(2K 0 ) . (b) Comparison between different ramp times t f for a fixed value of τ = 3. The vertical dashed line is the bound ξB = 2(τ 3/2 -1).


PhD Cédric Coulouarn
email: cedric.coulouarn@inserm.fr

Bruno Clément

Stellate cells and the development of liver cancer; therapeutic potential of targeting the stroma

Keywords: HCC, hepatocellular carcinoma, ICC, intrahepatic cholangiocarcinoma, HSC, hepatic stellate cell, ECM, extracellular matrix, TGF , transforming growth factor beta, MMP, matrix metallopeptidase, EMT, epithelial to mesenchymal cell transition, PDGF, platelet-derived growth factor, VEGF, vascular endothelial growth factor, IL, interleukin Liver cancer, fibrosis, hepatic stellate cell, microenvironment, therapeutics, genomics

Liver carcinogenesis represents a paradigm to study the role of the microenvironment in cancer given that most tumors develop in a background of liver fibrosis/cirrhosis Tumor cell microenvironment remodeling is associated with tumor progression HSC play an important role in liver carcinogenesis as key modulators of fibrosis and tumor cell microenvironment

Targeting HSC and the crosstalk between tumor and stromal cells may represent a promising therapeutic strategy

Summary

Hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) are the most common types of primary tumors in the liver. Although major advances have been made in understanding the cellular and molecular mechanisms underlying liver carcinogenesis, HCC and ICC are still deadly cancers worldwide waiting for innovative therapeutic options. Growing evidences from the literature highlight the critical role of the tumor cell microenvironment in the pathogenesis of cancer diseases. Thus, targeting the microenvironment, particularly the crosstalk between tumor cells and stromal cells, has emerged as a promising therapeutic strategy. This strategy would be particularly relevant for liver cancers which frequently develop in a setting of chronic inflammation and microenvironment remodeling associated with hepatic fibrosis and cirrhosis, such processes in which hepatic stellate cells (HSC) greatly contribute. This review brings a genomic point of view on the alterations of the cellular microenvironment in liver cancers, particularly the stromal tissue within tumor nodules, emphasizing the importance of the crosstalk between tumor cells and stromal cells, notably activated HSC, in tumor onset and progression. Furthermore, potential therapeutic modalities of targeting the stroma and HSC are discussed.

Introduction

Growing evidences from genetic, genomic and cell-biology indicate that tumorigenesis is determined not only by malignant cells but also by their microenvironment [START_REF] Hanahan | Accessories to the crime: functions of cells recruited to the tumor microenvironment[END_REF]. The microenvironment is a complex and dynamic system involving extracellular matrix (ECM) components, soluble factors, and stromal cells, whose distribution and composition vary in space and time [START_REF] Hanahan | Accessories to the crime: functions of cells recruited to the tumor microenvironment[END_REF][START_REF] Bhowmick | Stromal fibroblasts in cancer initiation and progression[END_REF][START_REF] Junttila | Influence of tumour micro-environment heterogeneity on therapeutic response[END_REF]. Under physiological condition, the microenvironment serves as an important barrier to epithelial cell transformation, notably by maintaining cell polarity and by controlling cell proliferation [START_REF] Hanahan | Accessories to the crime: functions of cells recruited to the tumor microenvironment[END_REF][START_REF] Bhowmick | Stromal fibroblasts in cancer initiation and progression[END_REF][START_REF] Junttila | Influence of tumour micro-environment heterogeneity on therapeutic response[END_REF]. In response to emerging epithelial cancerous lesions, the microenvironment experiences important changes (e.g. recruitment/activation of stromal cells, ECM remodeling) which contribute to cancer initiation and progression and influence the therapeutic response [START_REF] Hanahan | Accessories to the crime: functions of cells recruited to the tumor microenvironment[END_REF][START_REF] Bhowmick | Stromal fibroblasts in cancer initiation and progression[END_REF][START_REF] Junttila | Influence of tumour micro-environment heterogeneity on therapeutic response[END_REF]. Thus, targeting the tumor microenvironment is now viewed as a promising strategy to treat cancer in a variety of organs including liver [START_REF] Junttila | Influence of tumour micro-environment heterogeneity on therapeutic response[END_REF][START_REF] Hernandez-Gea | Role of the microenvironment in the pathogenesis and treatment of hepatocellular carcinoma[END_REF]. Hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) are the two major types of primary tumors in the liver. Alteration of the microenvironment is a hallmark of liver carcinogenesis given that more than 80% of tumors arise in a setting of chronic inflammation associated with liver fibrosis and/or cirrhosis, such conditions which constitute real precancerous stages [START_REF] Hernandez-Gea | Role of the microenvironment in the pathogenesis and treatment of hepatocellular carcinoma[END_REF].

As key drivers of liver fibrosis and ECM remodeling [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF], activated hepatic stellate cells (HSC) might represent attractive targets in the design of innovative therapeutic strategies against the stroma in liver carcinogenesis.

The tumor microenvironment in liver carcinogenesis

Tumor microenvironment includes cellular and non-cellular components. In the liver, HSC, fibroblasts, myofibroblasts as well as immune and endothelial cells represent the main cell types of the hepatocyte microenvironment [START_REF] Hernandez-Gea | Role of the microenvironment in the pathogenesis and treatment of hepatocellular carcinoma[END_REF]. In addition to ECM macromolecules (e.g. collagens, proteoglycans), non-cellular components include diverse soluble factors such as cytokines and growth factors that can be stored into the ECM and orchestrate the interplays between tumor cells and the microenvironment [START_REF] Hanahan | Accessories to the crime: functions of cells recruited to the tumor microenvironment[END_REF][START_REF] Bhowmick | Stromal fibroblasts in cancer initiation and progression[END_REF][START_REF] Junttila | Influence of tumour micro-environment heterogeneity on therapeutic response[END_REF][START_REF] Hernandez-Gea | Role of the microenvironment in the pathogenesis and treatment of hepatocellular carcinoma[END_REF].

Combination of cell and molecular biology, biochemistry, histopathology and gene to gene approaches greatly contributed to identify pathways deregulated in the tumor stroma and their impact on tumor cells [START_REF] Hanahan | Accessories to the crime: functions of cells recruited to the tumor microenvironment[END_REF]. Recently, genomic approaches revisited the field allowing an exhaustive and integrated view of these deregulations at a pangenomic scale [START_REF] Place | The microenvironment in breast cancer progression: biology and implications for treatment[END_REF]. Even more, by combining laser microdissection and gene expression profiling, stromal gene signatures linked to clinical outcomes were established in cancer [START_REF] Place | The microenvironment in breast cancer progression: biology and implications for treatment[END_REF]. This approach was proven to be fruitful for deciphering the molecular mechanisms underlying the alterations of the tumor microenvironment, with the ultimate goal of designing new therapeutic approaches, and identifying novel diagnostic and prognostic biomarkers [START_REF] Place | The microenvironment in breast cancer progression: biology and implications for treatment[END_REF]. In liver, few studies addressed this issue at a genomic scale. In HCC, gene expression profiling highlighted the importance of Th1 and Th2 cytokines in the surrounding non-tumor tissue of HCC associated with metastasis [START_REF] Budhu | Prediction of venous metastases, recurrence, and prognosis in hepatocellular carcinoma based on a unique immune response signature of the liver microenvironment[END_REF]. A metastasisinclined microenvironment signature was characterized by an increase in Th2 cytokines and a decrease in Th1 cytokines [START_REF] Budhu | Prediction of venous metastases, recurrence, and prognosis in hepatocellular carcinoma based on a unique immune response signature of the liver microenvironment[END_REF]. This study suggested that the dynamics of the immune microenvironment in the non-tumor tissue adjacent to the tumor nodules may result in the establishment of a suitable niche to promote tumor cell dissemination.

Genomic studies also provided molecular insights into the pathogenesis of ICC which is usually characterized by a dense desmoplastic stroma [START_REF] Andersen | Genetic profiling of intrahepatic cholangiocarcinoma[END_REF]. From these studies clinically relevant ICC subgroups were highlighted and new therapeutic opportunities were proposed, based on BRAF/KRAS mutations and activation of oncogenic pathways (e.g. receptor tyrosine kinases) [START_REF] Andersen | Genetic profiling of intrahepatic cholangiocarcinoma[END_REF]. Recently, we identified specific alterations of the stroma in ICC through an unsupervised analysis of microdissected human tumors [START_REF] Sulpice | Molecular profiling of stroma identifies Osteopontin as an independent predictor of poor prognosis in intrahepatic cholangiocarcinoma[END_REF]. Thus, a signature which included genes related to cell cycle, ECM and transforming growth factor beta (TGFβ) pathways was shown to significantly discriminate the tumor stroma from fibrous tissue isolated in the adjacent non tumor liver. A clear correlation between genomic changes in the stroma and the aggressiveness of ICC was also demonstrated.

Notably, high stromal expressions of osteopontin and TGFβ were identified as poor prognosis factors [START_REF] Sulpice | Molecular profiling of stroma identifies Osteopontin as an independent predictor of poor prognosis in intrahepatic cholangiocarcinoma[END_REF]. Besides promising biomarkers, osteopontin and TGFβ represent potential therapeutic targets given their proven role in driving the oncogenic process, from early stages of tumor development to late invasive stages. Indeed, gain and loss of function studies demonstrated osteopontin to be crucial for tumor cell growth and metastasis, notably by mechanisms involving apoptosis escape, angiogenesis, and ECM degradation [START_REF] Cao | Osteopontin as potential biomarker and therapeutic target in gastric and liver cancers[END_REF]. Activation of the TGFβ signaling was found in HCC [START_REF] Coulouarn | Transforming growth factor-beta gene expression signature in mouse hepatocytes predicts clinical outcome in human cancer[END_REF], ICC [START_REF] Sulpice | Molecular profiling of stroma identifies Osteopontin as an independent predictor of poor prognosis in intrahepatic cholangiocarcinoma[END_REF] and combined HCC-ICC [START_REF] Coulouarn | Combined hepatocellular-cholangiocarcinomas exhibit progenitor features and activation of Wnt and TGFβ signaling pathways[END_REF]. Importantly, studies using engineered mice demonstrated that the modulation of the TGFβ pathway in stromal fibroblasts influence the oncogenic potential of the adjacent epithelial cells [START_REF] Bhowmick | Stromal fibroblasts in cancer initiation and progression[END_REF]. These results imply that genomic alterations in stromal cells may result in tumor initiation and progression.

HSC in tumor onset and progression

The activation of HSC and subsequent phenotypic changes towards a myofibroblast-like phenotype is a key event in liver fibrosis [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF]. Gene expression studies showed that activated HSC markedly express genes involved in fibrogenesis and fibrolysis, inflammation and apoptosis [START_REF] De Minicis | Gene expression profiles during hepatic stellate cell activation in culture and in vivo[END_REF]. HSC activation is controlled by numerous factors and signaling pathways (e.g. TGFβ, platelet-derived growth factors (PDGF), hedgehog, notch, microRNAs) [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF]. Recently, the hedgehog signaling was shown to control the fate of HSC, thus opening new opportunities for a therapeutic targeting of HSC [START_REF] Chen | Hedgehog controls hepatic stellate cell fate by regulating metabolism[END_REF]. The nuclear factor-kappa B (NF-κB) pathway has been also reported to contribute to HSC activation and survival, and more largely to be a central factor in the progression of hepatic diseases, linking liver injury, inflammation, fibrosis and HCC (reviewed in [START_REF] Luedde | NF-κB in the liver-linking injury, fibrosis and hepatocellular carcinoma[END_REF]).

Besides a major role in fibrogenesis, HSC exhibit biological functions that influence the onset and the progression of HCC [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF]. Thus, HSC can induce phenotypic changes in cancer cells, notably through the production of growth factors and cytokines in favor of tumor cell proliferation (e.g. hepatocyte growth factor, interleukin-6 (IL-6)) [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF][START_REF] Kang | Hepatic stellate cells: partners in crime for liver metastases?[END_REF].

Migration and proliferation of HCC cells are also modulated by ECM components produced by activated HSC, including basement membrane components, e.g. laminin-5 [START_REF] Santamato | Hepatic stellate cells stimulate HCC cell migration via laminin-5 production[END_REF]. Interestingly, HSC were reported as key players in liver tumorigenesis associated with the gut-liver axis [START_REF] Dapito | Promotion of hepatocellular carcinoma by the intestinal microbiota and TLR4[END_REF]. Thus, the gut microbiome was shown to induce inflammatory and fibrogenic responses, and HSC activation leading to the production of epiregulin, a mitogenic factor for hepatocytes [START_REF] Dapito | Promotion of hepatocellular carcinoma by the intestinal microbiota and TLR4[END_REF]. Cellular and molecular approaches demonstrated that a bidirectional crosstalk exists between HSC-derived myofibroblasts and tumor hepatocytes [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF]. Early studies showed that the exposition of HSC to conditioned media derived from HCC tumor cells resulted in HSC activation, migration and expression of pro-angiogenic factors such as vascular endothelial growth factor alpha (VEGFA) [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF].

Recently, we reported that the crosstalk between hepatoma cells and activated HSC also increased the expression of proinflammatory cytokines and chemokines (e.g. IL-6, IL-8), and modified the phenotype of hepatoma cells toward motile cells, together with the generation of a permissive pro-angiogenic microenvironment, characterized by the overexpression of VEGFA and matrix metallopeptidase 9 (MMP9) in HSC [START_REF] Coulouarn | Hepatocyte-stellate cell cross-talk in the liver engenders a permissive inflammatory microenvironment that drives progression in hepatocellular carcinoma[END_REF].

Interestingly, integrative genomics demonstrated that a gene signature of this crosstalk was predictive of a poor prognosis and metastasis propensity in human HCC [START_REF] Coulouarn | Hepatocyte-stellate cell cross-talk in the liver engenders a permissive inflammatory microenvironment that drives progression in hepatocellular carcinoma[END_REF]. In addition to pro-inflammatory cytokines, TGFβ was reported to be central in driving the pro-tumorigenic effects of activated HSC on the progression of transformed hepatocytes [START_REF] Mikula | Activated hepatic stellate cells induce tumor progression of neoplastic hepatocytes in a TGF-beta dependent fashion[END_REF]. Interplay between HSC and cancer cells has been also reported in ICC, notably through the SDF1/CXCR4 axis which activation was shown to influence both cancer cell survival and metastasis [START_REF] Mikula | Activated hepatic stellate cells induce tumor progression of neoplastic hepatocytes in a TGF-beta dependent fashion[END_REF]. In addition to early stages of tumor development, HSC are involved in late tumor stages, notably by producing factors that directly participate in the formation of a pro-metastatic microenvironment [START_REF] Kang | Hepatic stellate cells: partners in crime for liver metastases?[END_REF]. Such factors in favor of the metastatic growth of tumor cells include inducers of the epithelial to mesenchymal cell transition (EMT), modulators of ECM synthesis and degradation, pro-angiogenic and immune-suppression factors (e.g. TGFβ, ECM proteins, MMP, VEGFA) [START_REF] Kang | Hepatic stellate cells: partners in crime for liver metastases?[END_REF]. HSC can produce immune-regulatory cytokines (e.g. MCP1, RANTES, CCL21) to promote chemotaxis, adherence and activation of inflammatory cells [START_REF] Friedman | Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver[END_REF][START_REF] Mallat | Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis[END_REF]. Paracrine interactions of HSC with endothelial cells have been reported, as well as the secretion of VEGFA and angiopoietins by HSC favoring a pro-angiogenic microenvironment [START_REF] Mallat | Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis[END_REF].

Therapeutic targeting of tumor microenvironment and HSC

Targeting the microenvironment is emerging as a promising strategy given the wellrecognized role of the stroma in carcinogenesis [START_REF] Junttila | Influence of tumour micro-environment heterogeneity on therapeutic response[END_REF]. Examples of drugs targeting the microenvironment include anti-angiogenic and anti-proliferative agents such as bevacizumab, an inhibitor of VEGFA, cetuximab, an inhibitor of EGFR, and sorafenib, an inhibitor of multiple protein kinase receptors (e.g. EGFR, VEGFR, PDGFR) [START_REF] Hernandez-Gea | Role of the microenvironment in the pathogenesis and treatment of hepatocellular carcinoma[END_REF].

Interestingly, sorafenib, which is currently the only drug recommended for advanced HCC, was shown to reduce the proliferation of transformed hepatocytes but also to attenuate liver fibrosis, notably by reducing HSC proliferation and ECM accumulation [START_REF] Wang | New insights into the antifibrotic effects of sorafenib on hepatic stellate cells and liver fibrosis[END_REF]. This observation opens an opportunity to target not only the tumor cells but also their microenvironment. One can expect that a better understanding of the cellular and molecular mechanisms underlying the process of HSC activation/proliferation, and ECM remodeling associated with tumor onset and progression may open opportunities to design new lines of therapeutic approaches. Therapeutic targeting of HSC has been investigated with interest given the key role HSC in fibrosis and HCC [START_REF] Mallat | Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis[END_REF]. Induction of cellular apoptosis or senescence and reversion of activated HSC toward a quiescent state have been proposed as mechanisms to clear activated HSC [START_REF] Mallat | Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis[END_REF]. As example, selective induction of HSC apoptosis may be achieved by nanoparticules or gene transfer systems designed to inhibit NF-B transcription factor which controls HSC activation and proliferation [START_REF] Luedde | NF-κB in the liver-linking injury, fibrosis and hepatocellular carcinoma[END_REF]. Boosting specific immune cell populations may represent another innovative strategy to control HSC. Recently, hepatic T-cells have been shown to promote the apoptosis of HSC through a mechanisms involving Fasligand [START_REF] Hammerich | Chemokine receptor CCR6-dependent accumulation of γδ T-cells in injured liver restricts hepatic inflammation and fibrosis[END_REF]. NK cells have been also shown to selectively kill early or senescent activated HSC and to produce anti-fibrotic cytokines such as IFN [START_REF] Mallat | Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis[END_REF]. Among immune effectors which exhibit anti-fibrotic potentials (e.g. IFN , IL-22, IL-10), IL22 was reported as a potent inducer of HSC senescence [START_REF] Mallat | Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis[END_REF].

Targeting the crosstalk between tumors cells and their microenvironment may also represent a promising therapeutic strategy. Exploring this possibility, we recently applied an integrative functional genomics approach to identify molecules that could interfere with the crosstalk between hepatocytes and HSC [START_REF] Coulouarn | Hepatocyte-stellate cell cross-talk in the liver engenders a permissive inflammatory microenvironment that drives progression in hepatocellular carcinoma[END_REF]. Thus, by using a connectivity map algorithm we were able to connect a gene signature of the hepatocyte-HSC crosstalk with trichostatin A, an inhibitor of histone deacetylases. Accordingly, the effects of the crosstalk on tumor cell migration and endothelial cell angiogenesis were reversed in presence of trichostatin A, suggesting that epigenetic modulators may be clinically relevant [START_REF] Coulouarn | Hepatocyte-stellate cell cross-talk in the liver engenders a permissive inflammatory microenvironment that drives progression in hepatocellular carcinoma[END_REF]. Soluble factors may be also targeted to modulate the communication between the tumor cells and the microenvironment. In that regard, TGF may represent a promising target given that this cytokine is involved in multiple stages of liver carcinogenesis. TGF exhibits both oncogenic and tumor suppressive properties depending on tumor stage [START_REF] Coulouarn | Transforming growth factor-beta gene expression signature in mouse hepatocytes predicts clinical outcome in human cancer[END_REF][START_REF] Giannelli | Inhibiting TGF-β signaling in hepatocellular carcinoma[END_REF]. As mentioned above, at preneoplastic stages TGF acts as a potent inducer of HSC activation and fibrogenesis but also exhibits growth-inhibitory and apoptosis-inducing effects, and in advanced stages TGF promotes HCC/ICC tumor cell invasion, notably as an inducer of EMT [START_REF] Coulouarn | Transforming growth factor-beta gene expression signature in mouse hepatocytes predicts clinical outcome in human cancer[END_REF][START_REF] Giannelli | Inhibiting TGF-β signaling in hepatocellular carcinoma[END_REF].

Thus, therapeutic targeting of the TGF pathway should be appropriately designed to inhibit its oncogenic properties while retaining its cytostatic effects. Targeting the TGF signaling by using small molecule inhibitors (e.g. LY2109761) or neutralizing antibodies has shown promising results in experimental HCC mouse models, including inhibition of cell invasion and abrogation of neo-angiogenesis [START_REF] Giannelli | Inhibiting TGF-β signaling in hepatocellular carcinoma[END_REF]. Inhibition of the TGF signaling was also reported to be effective in blocking tumor-stroma crosstalk and tumor progression in HCC [START_REF] Giannelli | Inhibiting TGF-β signaling in hepatocellular carcinoma[END_REF]. Thus, appropriately interfering with the crosstalk between cancer cells and their microenvironment may open new therapeutic opportunities in liver cancers (Figure 1).

Conclusive remark

Advances in understanding the molecular mechanisms involved in the crosstalk between tumor cells and their microenvironment at the pangenomic scale open the path to design new lines of therapeutic approach and associated biomarkers. Recent findings highlight that future adapted therapeutics would target both the tumor cells and the microenvironment by favorably modulating specific regulators in cellular pathways, and widespread mechanisms related to the neoplastic stroma evolution.

  Figure legend.

Figure 1 .Figure 1

 11 Figure 1. Therapeutic potential of targeting HSC and the stroma in liver cancer.

funding or conflict of interest with respect to this manuscript. Personal works were supported by grants from Inserm,