Alexander V Ereskovsky
email: alexander.ereskovsky@imbe.fr

Emmanuelle Renard

Carole Borchiellini

R Sommer

Cellular and molecular processes leading to embryo formation in sponges: evidences for high conservation of processes throughout animal evolution

Keywords: Porifera . Morphogenesis . Epithelial morphogenesis . Wnt pathway Sponge anatomy, histology, and cellular composition

Cellular and molecular processes leading to embryo formation in sponges: evidences for high conservation of processes throughout animal evolution

Alexander Ereskovsky, Emmanuelle Renard, Carole Borchiellini

 et al. 2005;[START_REF] Mercurio | Sessile and non-sessile morphs of Geodia cydonium (Jameson) (Porifera, Demospongiae) in two semi-enclosed Mediterranean bays[END_REF], some common features can be noted. Sponges have two cell layers named pinacoderm and choanoderm (Fig. 2), respectively, formed by pinacocytes and choanocytes. Pinacocytes are flattened cells covering the outer parts of the body (exopinacocytes and basopinacocytes) and lining the canals of the aquiferous system (endopinacocytes; Fig. 2). Choanocytes are flagellated collar cells, lining the filtering cavities of the aquiferous system called choanocyte chambers (Fig. 2). The space between the external pinacocyte layer and the aquiferous system is filled by the mesohyl, a loose layer composed of collagen fibrils, skeletal elements (the nature and form of which depends upon the taxa), and up to ten cell types with different degrees of motility [START_REF] Bond | Continuous cell movements rearrange anatomical structures in intact sponges[END_REF]; [START_REF] Bond | Locomotion of sponges and its physical mechanism[END_REF][START_REF] Ereskovsky | The comparative embryology of sponges[END_REF][START_REF] Harrison | Porifera. In: Harrison F (ed) Microscopic anatomy of invertebrates. 2: Placozoa, Porifera, Cnidaria and Ctenophora[END_REF][START_REF] Simpson | The cell biology of sponges[END_REF]. In contrast to this generally shared cellular organization, Hexactinellida harbor syncytial layers and reduced mesohyl [START_REF] Leys | The biology of glass sponges[END_REF].

In most sponges (Demospongiae, Calcarea, and Hexactinellida), these cell layers do not rely on a basement membrane, and cell junctions remain limited, septate junctions being present only in a few unusual cases: between the calcitedepositing sclerocytes in calcareous adult sponges [START_REF] Ledger | Septate junctions in the calcareous sponge Sycon ciliatum[END_REF] and between the spongocytes secreting the gemmule coat in freshwater sponges [START_REF] Vos | Study using the scanning electron microscope of the cells of the sponge, Ephydatia fluviatilis[END_REF]. These observations contrast with molecular data showing the presence of genes orthologous to those involves in eumetazoan adhesion elements. For example, the tetraspanin receptor and the scaffold protein MAGI were identified in Suberites domuncula (Demospongiae) [START_REF] Adell | Evolution of metazoan cell junction proteins: the scaffold protein MAGI and the transmembrane receptor tetraspanin in the demosponge Suberites domuncula[END_REF]).

In addition, the genome of the demosponge Amphimedon queenslandica contains the molecular components needed to form polarized cell layers with adherens junctions, but lacks the tools for occluding junctions or basal lamina. This suggests that cell layers of demosponges may share some but not all of the conserved characteristics of eumetazoan epithelia [START_REF] Fahey | Origin of animal epithelia: insights from the sponge genome[END_REF].

In contrast, in the fourth sponge clade Homoscleromorpha, cell layers are supported by a basement membrane consisting of collagen IV, tenascin, and laminin (Humbert-David and Garrone 1993; [START_REF] Boute | Type IV collagen in sponges, the missing link in basement membrane ubiquity[END_REF]. Furthermore, the cells are connected by specialized cell junctions, both in adult (Ereskovsky and Tokina 2007) and larvae [START_REF] Boury-Esnault | Larval development in Homoscleromorpha (Porifera, Demospongiae) first evidence of basal membrane in sponge larvae[END_REF][START_REF] Ereskovsky | Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)[END_REF]): thus, homoscleromoph cell layers can be considered as epithelia, of squamous type in adults and of columnar type in larva [START_REF] Ereskovsky | The comparative embryology of sponges[END_REF].

Reproduction and development in sponges

As in other animals, morphogenetic processes occur during ontogenesis in all sponges. For this reason, we review in this section the main developmental features of sponges. Most studied sponge species, whatever their lineage, are capable of both sexual and asexual reproduction, depending on season and environmental conditions [START_REF] Ereskovsky | The comparative embryology of sponges[END_REF]. [START_REF] Philippe | Phylogenomics revives traditional views on deep animal relationships[END_REF]. Another recent phylogenomic study (b) favors the paraphyly of sponges [START_REF] Sperling | Phylogenetic-signal dissection of nuclear housekeeping genes supports the paraphyly of sponges and the monophyly of Eumetazoa[END_REF]; for this reason, these relationships were indicated with dashed lines Fig. 2 Schematic representation of a sponge body plan (sponge with a leuconoid aquiferous system)

Sexual reproduction

In sponges, oviparous, ovoviviparous, and viviparous species can be found as well as hermaphroditic and gonochoristic species, so that the history of reproductive strategies is difficult to trace back. To date, no clear germinal cell lineage has been shown to exist in sponges; as far as we know, gametes differentiate either from archaeocytes (mesohyl cells generally considered as pluripotent) or from choanocytes. Because of the absence of specific gonopores, gametes are conducted outside or inside using the aquiferous system.

After fertilization, in the case of ovoviviparous and viviparous sponges, embryonic development takes place in temporary brood chambers (also referred to as follicles), bordered by flattened cells, that form at the end of vitellogenesis.

In other animals (Eumetazoa), embryogenesis is usually divided into five major stages: cleavage, blastulation, gastrulation, histogenesis, and organogenesis. In sponges, because of the lack of organs, the last step does not occur, and the other steps can hardly be distinguished from one another. As in other Metazoa, the first evident developmental step consists of cleavage. Four main cleavage patterns can be distinguished in sponges: (1) chaotic cleavage in Homoscleromorpha and most ovoviviparous Demospongiae; (2) radial-like cleavage in oviparous Demospongiae and Hexactinellida; (3) polyaxial cleavage in Halisarcida (Demospongiae) and Calcinea (Calcarea); and (4) incurvational cleavage in Calcaronea (Calcarea) [START_REF] Leys | Embryogenesis and larval differentiation in sponges[END_REF][START_REF] Ereskovsky | The comparative embryology of sponges[END_REF]. The spatial position of the blastomeres is usually unstable (except in calcaronean embryos); divisions either become asynchronous very early or are not synchronous at all.

At the end of cleavage, the other classically recognized stages are difficult or even impossible to identify. Firstly, a clear final phase of blastulation is lacking because at the stage commonly referred to as the blastula or the morula, the differentiation of larval cells begins (external ciliated cells and sclerocytes). Secondly, in sponges, the identification of gastrula stage or germ layers is still controversial [START_REF] Leys | Gastrulation in sponges[END_REF][START_REF] Ereskovsky | The problem of germ layers in sponges (Porifera) and some issues concerning early metazoan evolution[END_REF], due to conceptual divergences, difficult correspondence between embryological and adult structures, and high diversity of development types within sponge groups.

Moreover, the constant rearrangement of histological structures adds to the difficulty in determining cell and structural origins. However, aside from these technical and conceptual difficulties in clearly identifying homologous stages, it is evident that almost all types of cell movements characteristic of eumetazoan gastrulation are also found in the poriferan larval morphogenesis: morular delamination (Fig. 3a), cell delamination (Fig. 3b), unipolar and multipolar ingression (Fig. 3c), and invagination (Fig. 3d). In addition to these well-known cellular mechanisms, it is important to note that some poriferan specific morphogenetic processes can be defined: incurvation in Calcaronea (Fig. 3e), formation of blastula (pseudoblastula) by means of ingression of maternal cells into the cleaving embryo Chondrosia reniformis (Fig. 3f), polarized delamination (Fig. 3g), unipolar proliferation (Fig. 3h), and multipolar egression in Homoscleromorpha (Fig. 3i) [START_REF] Ereskovsky | The problem of germ layers in sponges (Porifera) and some issues concerning early metazoan evolution[END_REF].

All of the sponges studied [except the two demosponge genera Tetilla and Stylocordyla [START_REF] Watanabe | The development of two species of Tetilla (Demospongiae)[END_REF][START_REF] Sara | Viviparous development in the Antarctic sponge Stylocordyla borealis Loven, 1868[END_REF]] have indirect, i.e., larval development. Eight larval types have been described: coeloblastula, calciblastula, cinctoblastula, amphiblastula, disphaerula, hoplitomella, parenchymella, and trichimella [START_REF] Ereskovsky | On the reasons of ontogenesis pecularity in sponges[END_REF][START_REF] Maldonado | Phylum Porifera[END_REF][START_REF] Ereskovsky | The comparative embryology of sponges[END_REF]. With the exception of disphaerula, which is morphologically intermediate these larvae can either be hollow single-layered larvae (coeloblastula, calciblastula, cinctoblastula, and amphiblastula) or two-layered without cavity (parenchymella, hoplitomella, and trichimella).

From the larval stage, the attached adult stage is reached by a metamorphosis stage. This is a short stage of postembryonic development during which the larva undergoes radical morphological and physiological changes. Some structures, usually larval or provisional, disappear, while others, that are rudimentary or imaginal, rapidly complete their development. The main feature of metamorphosis is the acquisition of the sponge Bauplan, mainly characterized by the aquiferous system. The first adult structure to be formed de novo is the exopinacoderm, which isolates the young sponge from the environment. Subsequent steps include organization of the choanocyte chambers and the water current canals, the opening of the ostia and osculum, and the development of the elements of the adult skeleton. The detailed sequence of these events has only been described in a few species (for review, see [START_REF] Ereskovsky | The comparative embryology of sponges[END_REF].

Asexual reproduction

Asexual reproduction occurs in all poriferan clades. It may proceed by fragmentation, gemmulogenesis, and budding (for review, see [START_REF] Simpson | The cell biology of sponges[END_REF][START_REF] Fell | Porifera[END_REF][START_REF] Ereskovsky | The comparative embryology of sponges[END_REF].

Budding occasionally occurs in almost all sponges, regardless of taxonomic position or habitat [START_REF] Simpson | The cell biology of sponges[END_REF][START_REF] Fell | Porifera[END_REF]Ereskovsky and Tokina 2007). A general characteristic of the buds formed in most sponges (except the Homoscleromorpha lineage; Ereskovsky and Tokina 2007) is that in the initial stages of development, they are represented by a dense conglomerate of mobile mesohylar cells, mostly totipotent archaeocytes, at the surface of parent sponge. Their development passes by a mesenchymal morphogenesis (see below for details). Thus, a bud lacks choanocyte chambers, canals, and osculum (for review, see [START_REF] Fell | Porifera[END_REF]. After buds settle on the substrate, the aquiferous system forms and growth begins. In contrast, bud development in homoscleromorph sponges is based on epithelial morphogenesis (see below for details).

In all the sponges studied, gemmules develop from the same cell sources-totipotent archaeocytes conglomeration [START_REF] Simpson | The cell biology of sponges[END_REF][START_REF] Weissenfels | Biologie und Mikroskopische Anatomie der Süßwasserschwämme (Spongillidae)[END_REF].

Morphogenesis peculiarities: comparison with other metazoans

As previously specified, like other metazoans, sponges need morphogenetic mechanisms to shape their body during development and growth. Like other animals with continuous growth, morphogenetic processes occur throughout the lifespan.

Epithelial tissue organization is generally considered as a major innovation of Eumetazoa [START_REF] Tyler | Epithelium-the primary building block for metazoan complexity[END_REF][START_REF] Magie | Cell-cell adhesion in the Cnidaria: insights into the evolution of tissue morphogenesis[END_REF] because it has drastic consequences in terms of stem cells and the cell type specification system, as well as morphogenetic modes. As a corollary, it is thus usual to cite as the main difference between poriferans and eumetazoan the looseness of layers permitting a higher rate of cell migrations, leading to an almost permanent reorganization of tissue. Nevertheless, this is an oversimplification because one can expect Homoscleromorpha layers which can be considered as true epithelia to be subject to the same type of constraints than that encountered in eumetazoan. Therefore, a more thorough comparison between the four lineages of sponges and eumetazoans is necessary in order to better understand the evolution of cell layer behavior during morphogenetic processes.

Two main groups of morphogenesis in metazoans: epithelial and mesenchymal Epithelia and mesenchyme are two distinct tissue types existing in every Metazoa.

Epithelia are characterized by obvious apico-basal polarity, and the mechanical integrity of the tissue is ensured by adhesive junctions and the association with specialized extra cellular matrix (ECM), the basal lamina, providing structural support to cells and influencing their behavior [START_REF] Tyler | Epithelium-the primary building block for metazoan complexity[END_REF].

The formation of a continuous polarized cell sheet is one of the most basic forms of multicellular organization, and the epithelial blastoderm is the starting point for morphogenesis during the development of a wide range of Metazoa [START_REF] Lecuit | Orchestrating size and shape during morphogenesis[END_REF]. In contrast, the mesenchyme is composed of more motile, loosely associated fibroblast-like cells devoid of cellular junctions. Mesenchymal cells are clearly designed to move. They have a front-to-back polarity that positions leading-edge filopodia that pull cells forward. In relation to these two types of tissue organization, two main groups of morphogenesis are classically defined in metazoans: (1) morphogenetic movements of cell layers are known as epithelial morphogeneses [START_REF] Keller | How we are shaped: the biomechanics of gastrulation[END_REF]; and (2) morphogenetic movements of autonomous cells unconstrained by neighbors are referred to as mesenchymal morphogeneses [START_REF] Bauma | Transitions between epithelial and mesenchymal states in development and disease[END_REF].

Mesenchymal morphogenesis: epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transformations (MET)

The interconversion of epithelial and mesenchymal tissues can be found in a certain stage of embryonic development, as well as in malignant transformation of normal tissues [START_REF] Hay | An overview of epithelio-mesenchymal transformation[END_REF], and involves the profound phenotypic changes summarized below: Epithelial-mesenchymal transition (EMT) is central to the creation of numerous organs and complex tissues during embryonic development, asexual reproduction, and regeneration and has been well described in Eumetazoa [START_REF] Keller | How we are shaped: the biomechanics of gastrulation[END_REF][START_REF] Shook | Mechanisms, mechanics and function of epithelial-mesenchymal transitions in early development[END_REF][START_REF] Hay | The mesenchymal cell, its role in the embryo, and the remarkable signaling mechanisms that create it[END_REF]. For example, it occurs in the derivation of mesenchymal cells in Drosophila species from primary epithelia that have undergone an EMT during gastrulation [START_REF] Tepass | Epithelial cell polarity and cell junctions in Drosophila[END_REF]. As another example occurs in echinoid species in which the cells of primary skeletogenic mesenchyme migrate into the cavity of the coeloblastula [START_REF] Hardin | The role of secondary mesenchyme cells during sea urchin gastrulation studied by laser ablation[END_REF].

EMT requires the following profound changes in cell organization (Fig. 4): (1) cells must break the cell-cell cohesion, mediated, in part, by the interaction of cadherin molecules, at specialized cell junction regions called adherens junctions (AJ; reviewed in Kokkino et al. 2010) resulting in the loss of their apico-basal polarity;

(2) forces must be generated to drive cell delamination. The contraction of an apical actin-myosin belt [START_REF] Young | Dynamic changes in the distribution of cytoplasmic myosin during Drosophila embryogenesis[END_REF]) is often implicated, causing a shape change. (3) In order to migrate, delaminated cells must degrade basal lamina by protease activities [START_REF] Sternlicht | The matrix metalloproteinase stromelysin-1 acts as a natural mammary tumor promoter[END_REF][START_REF] Przybylo | Matrix metalloproteinase-induced epithelial-mesenchymal transition: tumor progression at Snail's pace[END_REF]. (4) As epithelial cells depend on the environmental and cellular context for their survival, growth, and division, changes in gene expression take place preventing apoptotic mechanisms from occurring after delamination [START_REF] Vega | Snail blocks the cell cycle and confers resistance to cell death[END_REF]). ( 5) EMT is accompanied by the expression of new adhesion and signaling molecules [START_REF] Oda | Dynamic behavior of the cadherinbased cell-cell adhesion system during Drosophila gastrulation[END_REF][START_REF] Moore | The role of chemoattraction in cancer metastases[END_REF], which guide the migrating cells and control the fate of mesenchymal cells (Fig. 4; [START_REF] Bauma | Transitions between epithelial and mesenchymal states in development and disease[END_REF]. Once free, individual mesenchymal cells usually develop a less well-defined morphology, which can be amoeboid or polarized [START_REF] Sahai | Differing modes of tumour cell invasion have distinct requirements for Rho/ROCK signaling and extracellular proteolysis[END_REF], and exhibit an invasive migratory phenotype. During the moving phase, these cells interact weakly with the surrounding ECM and with neighboring cells via transient adhesions [START_REF] Hay | The mesenchymal cell, its role in the embryo, and the remarkable signaling mechanisms that create it[END_REF]. Mesenchymal-epithelial transformation (MET) is the antithesis of EMT involving the participation of mesenchymal cells in the formation of epithelial structures [START_REF] Hay | The mesenchymal cell, its role in the embryo, and the remarkable signaling mechanisms that create it[END_REF]. The steps described earlier with regard to EMT occur in reverse order in MET (Fig. 4). MET transition plays a major role in certain steps of embryogenesis, metamorphosis, or during regeneration of tissues after injuries. A key role of E-cadherin in MET was demonstrated experimentally by transfection of vertebrate mesenchymal cells with plasmids carrying the E-cadherin gene [START_REF] Vanderburg | E-Cadherin transforms embryonic corneal fibroblasts to stratified epithelium with desmosomes[END_REF].

Epithelial morphogenesis classification

Epithelial morphogeneses are widely distributed among Eumetazoa, and various types of processes can be distinguished: (1) epithelization of spherical, poorly connected, embryonic cells; (2) inflexion of the epithelial layer (evagination, invagination, and folders formation); and (3) change in the area of the epithelial layer resulting from changing cell shape (spreading and fusion of epithelial sheets, convergent extension, epiboly, flattening, columnarization, elongation, and shortening; [START_REF] Keller | How we are shaped: the biomechanics of gastrulation[END_REF].

Known conserved molecular tools at the eumetazoan scale

As previously described, MET and EMT transitions that allow reorganization of tissues in Eumetazoa during either embryos, larvae, or adults life are mainly based on modifications of cell-cell or cell-ECM cohesion, cytoskeletal reorganization, and migration events. Many signaling pathways and transcription factors trigger EMT including different members of transforming growth factor-β (TGFβ), NF-κB, Wnt, Notch, and others interacting in complex ways not always fully understood [START_REF] Quintin | Epithelial morphogenesis in embryos: asymmetries, motors and brakes[END_REF][START_REF] Zallen | Planar polarity and tissue morphogenesis[END_REF][START_REF] Thiery | Epithelialmesenchymal transitions in development and disease[END_REF][START_REF] Lapébie | Dissecting the PCP pathway: one or more pathways? Does a separate Wnt-Fz-Rho pathway drive morphogenesis?[END_REF], which converge for the most part at the induction of the E-cadherin repressors. The numerous studies of tumor formations provide a basis for a better description of EMT transitions [START_REF] Ouyang | Molecular signaling of the epithelial to mesenchymal transition in generating and maintaining cancer stem cells[END_REF]. Nevertheless, most studies focus on vertebrates therefore generalization at the eumetazoan level is often difficult.

Morphogenesis in sponges

The literature provides numerous descriptions of different morphogenesis modes during embryo development, metamorphosis, and asexual reproduction in different sponge lineages. Nevertheless, it is regrettable that, because of current technical limitations, these cellular mechanisms have not been described in sufficient detail (see [START_REF] Ereskovsky | The comparative embryology of sponges[END_REF].

The equivalent of eumetazoan EMT and MET in sponges

Except in the specific case of Homoscleromorpha, no true epithelium exists in sponges because of the absence of basement membrane and limited cell junctions. Nevertheless, choanoderm and pinacoderm somehow behave like epithelia in the sense that cells are polarized and more or less linearly organized and cohesive. In this section, to both facilitate comparison of mechanisms with the previous section and respect the classical nomenclature, we will here use the term "epithelial-like" rather than "epithelial," consequently EMT will be replaced here by ELMT and MET by MELT. Both ELMT and MELT are widely distributed during all ontogenesis stages in all Porifera taxa.

EMLT

During the normal ontogeny of sponges, mesenchymal morphogenetic processes are known to occur: Lévi (1956) already described unipolar ingression in blastula of Halisarca dujardini (Demospongiae). In the same species, ELMT was also described later at various steps of development: apolar ingression of outer cells into the blastocoel occur as well as cell internalization during the later stages of embryonic development and even in the free-swimming larva [START_REF] Ereskovsky | New data on embryonic development of Halisarca dujardini Johnston, 1842 (Demospongiae, Halisarcida)[END_REF]Gonobobleva and Ereskovsky 2004a). This suggests that the pool of internal cells may be constantly replenished by dedifferentiated external cells of the embryo and the larva (Fig. 5). ELMT can also be observed during the metamorphoses of different larval types in other sponges: in calciblastula (Calcarea and Calcinea), coeloblastula, and parenchymella (Demospongiae; Ereskovsky 2010). Indeed, after settlement of the larva, disorganization of the outer cell layer occurs with desintegration into separate cells. The separated cells acquire amoeboid shape and migrate to the inner part of the larva, forming a dense conglomerate (Fig. 6), in which some cells will retain the ultrastructural characteristics of the larval ciliated cells (Fig. 6) while others remain as dedifferentiated amoeboid cells. This phenomenon has been described in detail in H. dujardini (Gonobobleva and Ereskovsky 2004b) and in some Homoscleromorpha species (Ereskovsky et al. 2007[START_REF] Ereskovsky | Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)[END_REF].

Like the primary mesenchymal cells of echinoids, the migrating cells of homoscleromorph Plakina trilopha become club-shaped, with rounded proximal parts, and their distal ends sprout long protrusions. During this process, intercellular contacts are destroyed, and pseudopodia are formed in the proximal part of the future mesohylar cell [START_REF] Ereskovsky | Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)[END_REF].

MELT

In contrast to ELMT, mesenchymal-epithelial-like transition (MELT) is rarer during sponge embryogenesis. It has been observed during multipolar egression in Homoscleromorpha [START_REF] Ereskovsky | Cleavage pattern in Oscarella species (Porifera, Demospongiae, Homoscleromorpha): transmission of maternal cells and symbiotic bacteria[END_REF][START_REF] Maldonado | Reproductive output in a Mediterranean population of the homosclerophorid Corticium candelabrum (Porifera, Demospongiae), with notes on the ultrastructure and behavior of the larva[END_REF], where after the formation of an apolar morula, internal blastomers migrate to the periphery of the embryo resulting in the formation of a hollow singlelayered pre-larva (Fig. 3i).

Interestingly, this mechanism observed in Homoscleromorpha is similar to that of schizocoely, a process widespread among the Eumetazoa, for example, during formation of the endodermal lining in cnidarian medusae through buds [START_REF] Boero | The cnidarian premises of metazoan evolution: from triploblasty, to coelom formation, to metamery[END_REF], and by the formation of coelomic cavities in annelids [START_REF] Anderson | Embryology and phylogeny in annelids and arthropods[END_REF].

In other sponge lineages, MELT is involved in the development of the aquiferous system during metamorphosis. During metamorphosis of calciblastula, coeloblastula, and parenchymella, the choanoderm and endopinacoderm are formed by migration of separate cells from internal cell conglomerate, and their association is followed by differentiation (Fig. 7; Ereskovsky 2010). These mesenchymal movements to form epithelial-like structures have been well described for example, in H. dujardini and A. queenslandica [START_REF] Leys | Embryogenesis and metamorphosis in a haplosclerid demosponge: gastrulation and transdifferentiation of larval ciliated cells to chanocytes[END_REF]Gonobobleva and Ereskovsky 2004b).

Epithelial or epithelial-like morphogenesis in sponges

With or without true epithelia, the processes are similar to those of eumetazoans

The formation of the continuous epithelial (Homoscleromorpha) or epithelial-like (other cellular sponges) sheets The coeloblastula of the calcareous sponges Guancha arnesenae [START_REF] Ereskovsky | Larval development in Guancha arnesenae (Porifera, Calcispongiae, Calcinea)[END_REF] and of the demosponges Polymastia robusta [START_REF] Borojevic | La ponte et le développement de Polymastia robusta (demosponges)[END_REF]) and H. dujardini (Gonobobleva and Ereskovsky 2004a) consist of a columnar layer of polarized cells closely adjoined, but without specialized intercellular junctions at this stage.

In contrast, in homoscleromorphs (Ereskovsky 2010), the pre-larva shows a surface cell layer looking like palisade epithelium: highly polarized (cilium in the apical part and collagen synthesis in the basal part), tightened by specialized intercellular contacts in the apical zone (zonula adherens), and lined by a basement membrane [START_REF] Boury-Esnault | Larval development in Homoscleromorpha (Porifera, Demospongiae) first evidence of basal membrane in sponge larvae[END_REF].

Inflexion of the layers: invagination and evagination

Epithelial folding is a basic morphogenetic process reiterated throughout all types of development in Eumetazoa [START_REF] Wolpert | Principles of development[END_REF]. During this processes, interactions between epithelial cells and the extracellular matrix play a fundamental role. Two main types of movements are commonly defined: invagination and evagination. Invagination is the inpocketing or furrow formation at a specific region of an epithelium, with the apical surface being the concave side. In contrast, evagination is the outpocketing or ridge formation within an epithelium such that the apical surface is the convex side of the pocket.

Both processes are rare during embryonic development of sponges, except in Homoscleromorpha where they occur quite often. In this sponge lineage invagination occurs during folder formation in pre-larva, both invagination and evagination occur during aquiferous system development in metamorphosing larva, the exopinacoderm invagination occurs during ostia formation, and evagination occurs during the first steps of budding during asexual reproduction and lobe formation phase of sponge growth (see [START_REF] Ereskovsky | The comparative embryology of sponges[END_REF]. Even if functional evidence is still lacking, the presence of a basement membrane may be expected to be partly responsible for this observation.

Focus on invaginations Invagination of cell layers in sponges can be performed by two distinct phenomena linked with two different cell shape modifications: (1) invagination involving bottle-shaped cells. The function of so-called wedge-shaped or bottle cells is critical to the proper initiation of invagination in metazoans, for example, in echinoids [START_REF] Kimberly | Bottle cells are required for the initiation of primary invagination in the sea urchin embryo[END_REF], and in anthozoans [START_REF] Kraus | Gastrulation in the sea anemone Nematostella vectensis occurs by invagination and immigration: an ultrastructural study[END_REF]; and (2) invagination resulting from the increase in the surface area, a mechanism that also occurs in Eumetazoa, for example, during the neurulation in cephalochordates (Whitakker 1997).

The first mechanism is a key morphogenetic event occurring during metamorphosis of all investigated homoscleromorphs cinctoblastulae (Fig. 7; fully detailed in Ereskovsky et al. 2007[START_REF] Ereskovsky | Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)[END_REF]. This morphogenesis often proceeds as a dome-shaped invagination of the settler's basal layer of cells that have retained the cilium. The bottle-shaped cells are formed in the zone of fold or invagination formation. During their migration, bottle cells do not lose junctions with neighboring cells. The basal (expanded) part of protruded cells extends and forms lamellopodia and filopodia, while the apical part plays an anchorage role in the epithelial layer because of zonula adherens. The result of these cell movements is that the marginal flattened parts of the settler tuck up or down, merging either above the apical pole or below the basal pole. Thus, the rhagon acquires a second internal cell layer that develops into the aquiferous system. Canals of aquiferous system and endopinacoderm are derived from the proximal parts of the internal cell layer (Fig. 7, label D). The choanocyte chambers develop from distal parts of the internal folds (Fig. 7, label E).

The second mechanism of invagination has been well described during embryonic development of H. dujardini (Fig. 3d; Ereskovsky and Gonobobleva 2000; Gonobobleva and ). In this case, the larval outer cells proliferate, actively yielding to numerous folds and protrusions of the surface layer. After the end of proliferation and the acquisition of disphaerula cell characteristics, the invagination of the ciliated layer proceeds perpendicularly to the anterior-posterior axis of the larva and results in a single-layered closed structure formed by ciliated cells, with their cilia directed inwards.

Focus on evagination

The mechanism of evagination (synonyms: incurvation and inversion) is well known in Eumetazoa, for example, during an early development (in blastulae) of Nematostella vectensis [START_REF] Fritzenwanker | Early development and axis specification in the sea anemone Nematostella vectensis[END_REF], during asexual bud formation and tentacle development in Hydra [START_REF] Philipp | Wnt/beta-catenin and noncanonical Wnt signaling interact in tissue evagination in the simple eumetazoan Hydra[END_REF], or in imaginal disc development of Drosophila melanogaster [START_REF] Fristrom | The mechanism of evagination of imaginal discs of Drosophila melanogaster: I. General considerations[END_REF]. In sponges, it is characteristic for Calcaronea (class Calcarea) embryos (Fig. 8) [START_REF] Duboscq | L'ovogenèse, la fécondation et les premiers stades du développement des Eponges calcaires[END_REF]. Recent light and electron microscopic observations on Sycon ciliata [START_REF] Franzen | Oogenesis and larval development of Scypha ciliata (Porifera, Calcarea)[END_REF] and Sycon calcaravis [START_REF] Yamasaki | Involvement of maternal choanocyte during embryogenesis in Sycon calcar-avis, Calcarea, Porifera[END_REF] show that inversion in syconoid calcaroneans results from coordinated movements of the layer of parent choanocytes and the granular cells of the stomoblastula. At the beginning of inversion in S. ciliata, the choanocytes lose the collar and the flagellum, and their basal parts produce long flattened offshoots spreading along the embryo (Fig. 8a,b). Such transformed choanocytes establish contacts with granular stomoblastula macromeres, which, in turn, spread filopodia towards the former. As a result of this interaction, the mass of granular cells is drawn into the choanocyte chamber. Transformed flattened choanocytes migrate along the external surface of the stomoblastula, pulling the granular cells along with them and making the stomoblastula turn inside out. At the end of inversion, the larva lies within the choanocyte chamber (Fig. 8d).

Changes of cell shapes involved

As mentioned previously, changes of cell shape often occur during morphogenetic processes and often play central roles. Spreading and fusion of cell layers and convergent extension are often accompanied by the flattening, columnarization, elongation, and shortening of cells. Even if all these events are rarely observed in the main three lineages of sponges, the majority of these morphogenetic mechanisms are more widely distributed in homoscleromorphs as well as in Eumetazoa.

Flattening versus columnarization A common cell shape change during epithelial morphogenesis is the shortening of the lateral sides of a cell. This event results in the flattening of the epithelial sheet such that the epithelium increases its apical and basal surfaces (Schöck and Perrimon 2002). Well-known examples are the flattening in the epiboly of frog embryos and flattening that occurs during the formation of the wing blades in insects [START_REF] Fristrom | The cellular basis of epithelial morphogenesis. A review[END_REF].

Clear examples of flattening in sponges, and especially in Homoscleromorpha, are found in metamorphosis of larvae, bud formation, and in reparative regeneration of the exopinacoderm (described in Oscarella lobularis). In contrast, the reverse process, columnarization, is more unusual.

Three main mechanisms of flattening have been described so far: (1) the columnar larval epithelium of homoscleromorph cinctoblastula, flatten during the first step of metamorphosis accompanying cell dedifferentiation. Cells first change from columnar to cubical then from cubical to flat. This results in the extension of the surface area of the settler. The cell junctions and basement membrane remain intact throughout the flattening process (Ereskovsky et al. 2007[START_REF] Ereskovsky | Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)[END_REF]; (2) during the metamorphosis of P. trilopha, a "cytoplasmic shedding" was described [START_REF] Ereskovsky | Morphogenesis accompanying larval metamorphosis in Plakina trilopha (Porifera, Homoscleromorpha)[END_REF]). Here, the cell shape changes from prismatic to almost cubical due not only to the flattening of cells but also due to the cytoplasmic shedding and the decrease of cell volume; and (3) during the metamorphosis of the demosponge H. dujardini, an "oblique" type of contact cell polarization is involved. Here, it is interesting to note that the ciliated cells in the posterior larval hemisphere retain specialized intercellular contacts of the zonula adherens type (fully detailed in Gonobobleva and Ereskovsky 2004b). Whereas the two latter flattening mechanisms seem rare in other sponges, they are very common in eumetazoan morphogenesis [START_REF] Mergner | Chapter 1: Cnidaria. In: Reveberi G (ed) Experimental embryology of marine and fresh-water invertebrates[END_REF][START_REF] Beloussov | The dynamic architecture of a developing organism[END_REF]).

Spreading and fusion

The movement and fusion of epithelial sheets can be subdivided into three distinguishable and related steps: first, leading cells are specified and brought into position; second, cells execute a coordinated forward movement by changing shape and/or migrating over a substratum; and third, epithelial cells fuse. Many of these processes have been well described in Metazoa, such as epiboly during neural tube and palate closure in vertebrates [START_REF] Harrington | Comparative analysis of neurulation: first impressions do not count[END_REF], or during ventral enclosure in Caenorhabditis elegans [START_REF] Raich | Rapid epithelial-sheet sealing in the Caenorhabditis elegans embryo requires cadherindependent filopodial priming[END_REF]. Extensive and directed movements of two epithelial faces are then involved. One of the characteristics of this phenomenon is the formation of filopodia, originating from cells that are located at the leading edge of a cell sheet. When the epithelial sheets meet, nascent junctions form by rapid contacts. This "filopodial priming" leads to a rapid creation of adherens junctions. Spreading and fusion processes have been described in Homoscleromorpha. They occur, for example, in the follicle formation of eggs. Follicles form during the later stages of egg vitellogenesis when endopinacocytes surround mature eggs and embryos. During follicle formation, leading edge cells of the endopinacoderm appear at the border between two layers of endopinacocytes from adjoining exhalant canals [START_REF] Ereskovsky | Cleavage pattern in Oscarella species (Porifera, Demospongiae, Homoscleromorpha): transmission of maternal cells and symbiotic bacteria[END_REF].

Have molecular tools been conserved at the metazoan level?

Review of the main molecular tools used in eumetazoans and in early sponge Evo-Devo

The confirmation by molecular data of the phylogenetic position of sponges within the metazoan clade has made it possible to consider that the molecular bases of pluricellularity, development, and morphogenesis were probably acquired in the common ancestor of all the animals including Porifera. As far as eumetazoan morphogenesis is concerned, at the cellular level, these complex phenomena can be dissected in terms of cellular differentiation, migration, adhesion, and coordination. These cellular mechanisms have been shown to be regulated by two main types of molecular tools: transcription factors and signaling pathways.

Although sponge embryology has been studied since the nineteenth century, developmental genetics began in the 1980s, and finally, the first study of developmental genes in sponges dates back only to 1993. The investigations first focused on the homeobox genes [START_REF] Degnan | The ets multigene family is conserved throughout the Metazoa[END_REF]. Even though the degenerate PCR approach proved to be long and difficult with sponges and did not allow the characterization of this gene family, this was the essential starting point to become aware, little by little, of the presence of the unexpected molecular richness regarding the relative morphoanatomical simplicity of sponges. The first description of a homeobox gene was made in a fresh water demosponge Ephydiatia fluviatilis [START_REF] Seimiya | Homeobox-containing genes in the most primitive Metazoa, the sponges[END_REF]) and on marine sponge Geodia cydonium [START_REF] Kruse | Molecular evidence for the presence of a developmental gene in the lowest animals: identification of a homeobox-like gene in the marine sponge Geodia cydonium[END_REF].

The first EST libraries and the beginning of the genome sequencing of the demosponge A. queenslandica in 2005 (Srivastava et al. 2010a) significantly increased the accumulation of data. These different studies revealed that sponges possess genes homologous to those acting in the eumetazoan developmental program. In this section, we propose to offer a short survey of the state of the art of knowledge of sponge transcription factors and signaling pathways, but it is clear that we are still far from understanding the roles of each actor and far from being able to depict a clear scenario. In particular, it should be emphasized that all the following data and interpretations are based on currently available genomic data obtained from a limited sampling of eukaryotic lineages, EST data for a few sponge species (thus non-exhaustive) and on a single sponge genome (one species not being representative of a whole group). Concerning the last point, one cannot rule out the possibility that the absence of a gene may be the result of a secondary loss specific to A. queenslandica or to the demosponges, as has already been evidenced for different genes [START_REF] Peterson | Poriferan ANTP genes: primitively simple or secondarily reduced?[END_REF][START_REF] Gazave | NK homeobox genes with choanocyte-specific expression in homoscleromorph sponges[END_REF][START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF][START_REF] Schierwater | Concatenated analysis sheds light on early metazoan evolution and fuels a modern "urmetazoan" hypothesis[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF]. Moreover, the proposed scenarios must be viewed with caution because interpretation of the data relies on a phylogenetic context [START_REF] Schierwater | Concatenated analysis sheds light on early metazoan evolution and fuels a modern "urmetazoan" hypothesis[END_REF], and unfortunately, the relationships between the four extant lower metazoan phyla (Placozoa, Porifera, Cnidaria, and Ctenophora) still remain controversial [START_REF] Dunn | Broad phylogenomic sampling improves resolution of the animal tree of life[END_REF][START_REF] Hejnol | Assessing the root of bilaterian animals with scalable phylogenomic methods[END_REF][START_REF] Philippe | Phylogenomics revives traditional views on deep animal relationships[END_REF][START_REF] Philippe | Resolving difficult phylogenetic questions: why more sequences are not enough[END_REF][START_REF] Schierwater | Concatenated analysis sheds light on early metazoan evolution and fuels a modern "urmetazoan" hypothesis[END_REF][START_REF] Sperling | Phylogenetic-signal dissection of nuclear housekeeping genes supports the paraphyly of sponges and the monophyly of Eumetazoa[END_REF][START_REF] Mallatt | Nearly complete rRNA genes assembled from across the metazoan animals: effects of more taxa, a structure-based alignment, and paired-sites evolutionary models on phylogeny reconstruction[END_REF][START_REF] Pick | Improved phylogenomic taxon sampling noticeably affects nonbilaterian relationships[END_REF]. Another pitfall to be taken into account is the often encountered difficulty of assigning genes to known eumetazoan orthology groups.

Early or late origin of transcription factors?

Homeobox genes

The homeobox gene superfamily encodes transcription factors that, in eumetazoans, act as master regulators of development through their ability to activate or repress a diverse range of downstream target genes. Classes are defined on the basis of conservation of the homeodomains (HD, a 60 amino acid DNA-binding proteic domain) they encode, as well as additional motifs that contribute to DNA binding and interactions with other proteins. Not only in metazoans but also in all multicellular Eukaryotes, these transcription factors are extensively used in fundamental development processes and are highly diversified. They are supposed to have played a key role in the acquisition of multicellularity in Eukaryota [START_REF] Derelle | Homeodomain proteins belong to the ancestral molecular toolkit of eukaryotes[END_REF][START_REF] King | The unicellular ancestry of animal development[END_REF].

A recent extensive phylogenetical study of HD at the eukaryotic scale showed that HDs can be grouped in two clades: TALE (three extra residues between helix 1 and helix 2 of the homeodomain) and non-TALE. Moreover, these results show that the last common ancestor of Eukaryotes (LECA) already possessed these two types of HDs, non-TALE genes being lost secondarily in Monosiga [START_REF] Derelle | Homeodomain proteins belong to the ancestral molecular toolkit of eukaryotes[END_REF][START_REF] King | The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans[END_REF][START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF][START_REF] Sebé-Pedrós | Unexpected repertoire of metazoan transcription factors in the unicellular holozoan Capsaspora owczarzaki[END_REF]. Later, duplications occurred independently during diversification of eukaryotic lineages. As a result of this very wide diversification (by duplication and divergence, or via domain shuffling), animal homeobox genes are at present divided into 11 classes and more than 125 gene families, non-TALE genes being more diversified than TALE ones [START_REF] Holland | Classification and nomenclature of all human homeobox genes[END_REF][START_REF] Mukherjee | Comprehensive analysis of animal TAL homeobox genes: new conserved motifs and cases of accelerated evolution[END_REF][START_REF] Ryan | The homeodomain complement of the ctenophore Mnemiopsis leidyi suggests that Ctenophora and Porifera diverged prior to the ParaHoxozoa[END_REF].

Non-TALE genes Major diversification events of non-TALE genes occurred before metazoan radiation. Indeed, data on sponges revealed that many of non-TALE classes were already present in the metazoan ancestor, such as ANTP, PRD, POU, LIM, and SIX, and that others may have appeared later, after the Porifera-Eumetazoa divergence because, to date, no HNF, CUT, PROS, or CERS classes have been discovered in demosponges [START_REF] Larroux | Developmental expression of transcription factor genes in a demosponge: insights into the origin of metazoan multicellularity[END_REF][START_REF] Larroux | The NK homeobox gene cluster predates the origin of Hox genes[END_REF][START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF][START_REF] Ryan | Hox, Wnt, and the evolution of the primary body axis: insights from the early-divergent phyla[END_REF][START_REF] Ryan | The homeodomain complement of the ctenophore Mnemiopsis leidyi suggests that Ctenophora and Porifera diverged prior to the ParaHoxozoa[END_REF][START_REF] Degnan | Early evolution of metazoan transcription factors[END_REF]Srivastava et al. 2010aSrivastava et al. , 2010b)). Figure 9 gives a more detailed view of Non-TALE gene history.

TALE genes

The TALE category includes IRO, MEIS, PBX, and TGIF classes [START_REF] Holland | Classification and nomenclature of all human homeobox genes[END_REF][START_REF] Mukherjee | Comprehensive analysis of animal TAL homeobox genes: new conserved motifs and cases of accelerated evolution[END_REF]. In demosponges, several TALE genes have been characterized [START_REF] Perovic | Expression of one sponge Iroquois homeobox gene in primmorphs from Suberites domuncula during canal formation[END_REF][START_REF] Larroux | Developmental expression of transcription factor genes in a demosponge: insights into the origin of metazoan multicellularity[END_REF][START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF]. All but one seem to be related to the IRO class. [START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF] proposed that the common ancestor of Metazoa may have possessed at least two genes, resulting from a ancestral MEIS-like gene [START_REF] King | The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans[END_REF]). However, the data recently obtained on Capsaspora, although poorly supported, suggest the presence of a PBX class in the Holozoan ancestor and a secondary loss in Amphimedon and Monosiga [START_REF] Sebé-Pedrós | Unexpected repertoire of metazoan transcription factors in the unicellular holozoan Capsaspora owczarzaki[END_REF]). The interpretation is thus, once again, pending the acquisition of other genomic data.

Other transcription factors

Sponges also possess other TFs (Fig. 10), and evolutionary scenarios have been proposed for each of them. Generally, although many classes of transcription factors are older in origin [START_REF] Derelle | Homeodomain proteins belong to the ancestral molecular toolkit of eukaryotes[END_REF][START_REF] King | The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans[END_REF][START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF][START_REF] Shalchian-Tabrizi | Multigene phylogeny of choanozoa and the origin of animals[END_REF][START_REF] Degnan | Early evolution of metazoan transcription factors[END_REF][START_REF] Mikhailov | The origin of Metazoa: a transition from temporal to spatial cell differentiation[END_REF][START_REF] Sebé-Pedrós | Unexpected repertoire of metazoan transcription factors in the unicellular holozoan Capsaspora owczarzaki[END_REF], many other classes and families of transcription factors seem to be metazoan innovations. These animal genetic novelties are thought to have played an important role in animal evolution by providing new tools that increased morphogenetic possibilities. Nevertheless, as already mentioned, this impression of sudden emergence may only be the artificial result of insufficient sampling at the eukaryotic scale. In the same way, the lack of certain genes in the Amphimedon genome may not reflect the ancestral condition in sponges but rather specific gene losses [START_REF] Peterson | Poriferan ANTP genes: primitively simple or secondarily reduced?[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF]. To resolve this question, the acquisition of genomic data from other sponge lineages is needed. The most recent study on the subject, using the newly available genome of the sporozoan Capsaspora, led [START_REF] Sebé-Pedrós | Unexpected repertoire of metazoan transcription factors in the unicellular holozoan Capsaspora owczarzaki[END_REF] to propose a new very comprehensive evolutionary scenario (Fig. 10).

In other animals, ten TFs have been identified to be involved in EMT regulation during embryogenesis and carcinogenesis. Among them, some are direct repressors of the gene coding for E-cadherin (such as Snail, Twist, Fox, Gsc, and KLF). Interestingly, these TF are regulated by wellknown signaling pathways Wnt, Notch, TGF-β, and Hh [START_REF] Takebe | Targeting cancer stem cells by inhibiting Wnt, Notch, and Hedgehog pathways[END_REF].

Signaling pathways or how to make "new" from "old"

In multicellular organisms, signaling pathways are an essential intercellular means of communication enabling the realization and the coordination of the embryonic development and more broadly of morphogenetic processes. Cell Among these 20 pathways, only seven participate in the control of development processes: Wnt, TGF-β, Hedgehog (Hh), receptor tyrosine kinase (RTK), Jak/STAT, nuclear hormone receptor, and Notch [START_REF] Barolo | Three habits of highly effective signaling pathways: principles of transcriptional control by developmental cell signaling[END_REF][START_REF] Gerhart | Warkany lecture: signaling pathways in development[END_REF]. Complete descriptions of these pathways are the subject of several reviews (Adamska et al. 2007a(Adamska et al. , b, 2010[START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF][START_REF] Sakarya | A post-synaptic scaffold at the origin of the animal kingdom[END_REF]Richard et al. 2008;[START_REF] Gazave | Origin and evolution of the Notch signalling pathway: an overview from eukaryotic genomes[END_REF]Richard and Degnan 2009;Srivastava et al. 2010a).

Focus on the Wnt pathway

Among these major signaling molecules, the WNTs are metazoan-specific ligands that control diverse processes such as cell proliferation, cell-fate determination, cell migration, and differentiation during multiple steps of embryonic development. This key pathway is active in axis specification as well as in morphogenesis movements such as gastrulation processes in all the eumetazoan models studied and in the MET/EMT regulation [START_REF] Kusserow | Unexpected complexity of the Wnt gene family in a sea anemone[END_REF][START_REF] Guder | The Wnt code: cnidarians signal the way[END_REF][START_REF] Lee | A WNT of things to come: evolution of Wnt signaling and polarity in cnidarians[END_REF]Adamska et al. 2007a[START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF][START_REF] Momose | Two oppositely localised frizzled RNAs as axis determinants in a cnidarian embryo[END_REF][START_REF] Ryan | Hox, Wnt, and the evolution of the primary body axis: insights from the early-divergent phyla[END_REF][START_REF] Momose | A maternally localised Wnt ligand required for axial patterning in the cnidarian Clytia hemisphaerica[END_REF][START_REF] Manuel | Early evolution of symmetry and polarity in metazoan body plans[END_REF][START_REF] Takebe | Targeting cancer stem cells by inhibiting Wnt, Notch, and Hedgehog pathways[END_REF].

In the Amphimedon genome, the majority of the components of Wnt canonical or non-canonical signaling have been described (Adamska et al. 2007a[START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF][START_REF] Richards | The dawn of developmental signaling in the Metazoa[END_REF]Srivastava et al. 2010a). Nevertheless, a major diversification of some gene families is thought to have occurred after the demospongeseumetazoan split. Indeed, Amphimedon only possesses three Wnt gene families (assignation poorly corroborated) and two frizzled receptors (compared to the 12 Wnt and four frizzled receptors thought to be present in Ureumetazoa; [START_REF] Kusserow | Unexpected complexity of the Wnt gene family in a sea anemone[END_REF]. According to these first data (pending complementary data on other sponge and non-metazoan lineages), we can assume the presence of one to three Wnt genes in the last common metazoan ancestor. This assertion will have to be checked because Amphimedon has already been shown to have lost several key elements of both Wnt pathways, for example, dickkopf absent in Amphimedon but present in Oscarella carmela [START_REF] Nichols | Early evolution of animal cell signaling and adhesion genes[END_REF][START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF]. Whereas Wnt genes seem to be a metazoan synapomorphy, most of the other Wnt pathway components antedate the emergence of the metazoan lineage [START_REF] Putnam | Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization[END_REF]Fig. 11).

Despite the lack of specific protein-protein binding motifs required for interaction of ACP and Axin with each other and with β-catenin, it is thought likely that Wnt signaling is functional in sponges [START_REF] Richards | The dawn of developmental signaling in the Metazoa[END_REF][START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF]. It may be involved in axial patterning in demosponge embryos and in epithelium morphogenesis and patterning in Oscarella adults (Adamska et al. 2007a[START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF][START_REF] Lapébie | WNT/beta-catenin signalling and epithelial patterning in the homoscleromorph sponge Oscarella[END_REF][START_REF] Windsor | Wnt signaling and induction in the sponge aquiferous system: evidence for an ancient origin of the organizer[END_REF]. During the first phase of cell movements in Amphimedon blastula, the cells organize into two layers. The first cells to become distributed asymmetrically at the future posterior pole are those with strong expression of AmqWntA. The existence of a Wnt expression gradient in relation with embryonic polarization has been proposed in Amphimedon (Adamska et al. 2007a[START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF]. Functional studies on Ephydatia muelleri demonstrate the involvement of the Wnt pathway in the axial patterning of a gemmule-hatched juvenile (Windsor and Leys Fig. 10 Cladogram showing TF origin and evolution on phylogenetic hypothesis according to Sébé-Pedrós et al. (2011). Each color represents domain class. Origin of domain is indicated by a colored dot. Specific protein family appearance is indicated by a black-circled dot in our taxon sampling. Loss of the domain or specific protein family is indicated by a cross. Metazoan apomorphies are shown as black dots 2010). In juveniles treated with molecules simulating Wnt pathway activation (GSK3 inhibitors LiCl and alsterpaullone), the authors observed multiplication of oscula, which can be interpreted as multiplication of body axes. Since overactivation of the Wnt pathway in eumetazoan model systems commonly leads to the multiplication of the body axis [START_REF] Broun | Formation of the head organizer in hydra involves the canonical Wnt pathway[END_REF][START_REF] Müller | Wnt signaling inhydroid development: ectopic heads and giant buds induced by GSK-3beta inhibitors[END_REF][START_REF] Philipp | Wnt/beta-catenin and noncanonical Wnt signaling interact in tissue evagination in the simple eumetazoan Hydra[END_REF], the involvement of the Wnt pathway in axial establishment appears to be ancient in metazoan history. Pharmacological inhibition experiments have also been used to test the role of Wnt signaling in O. lobularis adults [START_REF] Lapébie | WNT/beta-catenin signalling and epithelial patterning in the homoscleromorph sponge Oscarella[END_REF]. The activation of the Wnt/βcatenin pathway using GSK3b inhibitors resulted in the formation of ectopic ostia, as in eumetazoan epithelial appendages [START_REF] Philipp | Wnt/beta-catenin and noncanonical Wnt signaling interact in tissue evagination in the simple eumetazoan Hydra[END_REF]). These results suggest that deployment of Wnt signaling in epithelial patterning and morphogenesis has been conserved after the divergence of Homoscleromorpha and Eumetazoa.

What is known concerning the others?

Similarly to Wnt signaling, the richness of sponges regarding TGF-β and Notch components is compatible with the functionality of these two pathways in sponges (Gazave et al. 2009;[START_REF] Richards | Sponge genes provide new insight into the evolutionary origin of the neurogenic circuit[END_REF][START_REF] Richards | The dawn of developmental signaling in the Metazoa[END_REF][START_REF] Adamska | Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF]Srivastava et al. 2010a). In contrast, too few components of Hedgehog and growth factors/receptors tyrosine kinase pathways have been found in Amphimedon (Fig. 11) support the hypothesis that they are active in this organism (Adamska et al. 2007b;[START_REF] Richards | The dawn of developmental signaling in the Metazoa[END_REF]. In this context, only Wnt, Notch, and TGF-β signaling pathways can at present be considered as metazoan synapomorphies. In these three cases, it has been shown that these metazoan innovations consist mainly of a new combination of oldest elements since most of the components and their parts predate the metazoan emergence. These innovative recombinations are the result of domain shuffling, gene duplications, and divergences but are also the result of lateral gene transfers [START_REF] Putnam | Sea anemone genome reveals ancestral eumetazoan gene repertoire and genomic organization[END_REF][START_REF] Gazave | Origin and evolution of the Notch signalling pathway: an overview from eukaryotic genomes[END_REF][START_REF] Richards | The dawn of developmental signaling in the Metazoa[END_REF][START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF]. The later additions of components in Eumetazoa are interpreted as the acquisition a more finely-turned method of regulating of the pathways [START_REF] Gazave | Origin and evolution of the Notch signalling pathway: an overview from eukaryotic genomes[END_REF][START_REF] Richards | The dawn of developmental signaling in the Metazoa[END_REF]. Except in the case of Wnt, described earlier, for which the first-albeit preliminaryfunctional data have been published, we can hardly propose concrete roles for these pathways in sponges.

It was pointed out that in other animals there are strong interrelations between EMT/MET, stem cell regulation and Wnt, Notch, Hh, and TGF-β interconnections. Moreover, according to data obtained during Amphimedon development, it seems that the interaction of key developmental pathways-such as Wnt, TGF-β, and Hedgehog-are also of ancient origin and could have emerged in the metazoan ancestor [START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF].

Main conclusions

In recent years, the first draft genome sequences from representatives of the earliest branching animals as well as nonmetazoan lineages have significantly altered our understanding of early animal evolution and the genomic complexity of the metazoan ancestor. A large majority of transcription factors and signaling pathways have their evolutionary origin at the base of the animal tree, including the acquisition of new genes (some of them via domain shuffling), gene cooption, or diversification of ancestral domains, in accordance with the acquisition of the multicellularity in this taxon.

Even if a very limited amount of expression and functional data is available for sponges, the initial data demonstrate that these developmental gene toolkits play a role in sponge development and morphogenesis [START_REF] Larroux | Developmental expression of transcription factor genes in a demosponge: insights into the origin of metazoan multicellularity[END_REF][START_REF] Larroux | The NK homeobox gene cluster predates the origin of Hox genes[END_REF][START_REF] Larroux | Genesis and expansion of metazoan transcription factor gene classes[END_REF]Adamska et al. 2007aAdamska et al. , b, 2010[START_REF] Adamska | What sponges can tell us about the evolution of developmental processes[END_REF][START_REF] Fahey | Does the high gene density in the sponge NK homeobox gene cluster reflect limited regulatory capacity?[END_REF][START_REF] Gauthier | The transcription factor NF-kappaB in the demosponge Amphimedon queenslandica: insights on the evolutionary origin of the Rel homology domain[END_REF][START_REF] Gazave | NK homeobox genes with choanocyte-specific expression in homoscleromorph sponges[END_REF][START_REF] Degnan | Early evolution of metazoan transcription factors[END_REF][START_REF] Lapébie | WNT/beta-catenin signalling and epithelial patterning in the homoscleromorph sponge Oscarella[END_REF]Richard and Degnan 2009;[START_REF] Windsor | Wnt signaling and induction in the sponge aquiferous system: evidence for an ancient origin of the organizer[END_REF][START_REF] Hill | Origin of Pax and Six gene families in sponges: single PaxB and Six1/2 orthologs in Chalinula loosanoffi[END_REF]Holstein et al. 2010;Srivastava et al. 2010a, b).

It is only through the sequencing of additional basal metazoan and non-metazoan Opisthokont genomes that we will be able to expand our understanding of the origin and evolution of TFs and signaling pathways, keeping in mind that the reconstruction of the evolutionary history of developmental processes would depend on still contentious nonbilaterian phylogenetic relationships. Another challenge is to establish tools for studying their function in sponges. The first published encouraging RNAi approaches are far from being routinely under control in each sponge model [START_REF] Rivera | RNA interference in marine and freshwater sponges: actin knockdown in Tethya wilhelma and Ephydatia muelleri by ingested dsRNA expressing bacteria[END_REF].

Conclusions and perspectives

Mechanistic similarities with eumetazoans: sponges are not so simple Finally, our review has attempted to show that morphogenetic processes found in sponges are as diverse and complex as those found in other animals. In true epithelial sponges (Homoscleromorpha), as well as in others, we find similar cell/layer movements, cellular shape changes involved in major morphogenetic processes such as embryogenesis, larval metamorphosis, or regeneration processes. Thus, sponges can provide information enabling us to better understand early animal evolution at the molecular level as well as at the cell/ cell layer level. Indeed, comparison of molecular tools will only be of value if accompanied by functional data and expression study during morphogenetic processes.

More than one sponge morphogenesis: The importance of models diversification By the variety of examples cited in the previous text, we have shown that each sponge lineage presents morphogenetic specificities. Homoscleromorpha are of special interest for comparison with eumetazoans because of their similar epithelial organization. Nevertheless, as previously demonstrated, even in the absence of a basement membrane, other sponge taxa also use very similar cellular mechanisms (even if epithelial morphogenesis is less represented). Thus, the comparison between different sponge taxa may help to determine the precise role of each type of cell adhesion tool or molecular element involved in morphogenetic mechanisms.

Pending questions

When did epithelia emerge?

The common answer to this question is that epithelia are a eumetazoan innovation. With regard to the Homoscleromorpha, the answer seems less clear. Until as recently as 2009, papers argued either in favor of monophyly [START_REF] Philippe | Phylogenomics revives traditional views on deep animal relationships[END_REF][START_REF] Schierwater | Concatenated analysis sheds light on early metazoan evolution and fuels a modern "urmetazoan" hypothesis[END_REF][START_REF] Pick | Improved phylogenomic taxon sampling noticeably affects nonbilaterian relationships[END_REF] or of paraphyly [START_REF] Hejnol | Assessing the root of bilaterian animals with scalable phylogenomic methods[END_REF][START_REF] Sperling | Phylogenetic-signal dissection of nuclear housekeeping genes supports the paraphyly of sponges and the monophyly of Eumetazoa[END_REF][START_REF] Mallatt | Nearly complete rRNA genes assembled from across the metazoan animals: effects of more taxa, a structure-based alignment, and paired-sites evolutionary models on phylogeny reconstruction[END_REF] of sponges. Depending on the phylogenetic relationships accepted, the interpretation of Homoscleromorpha epithelia relative to those of the Eumetazoa is very different: they may either be homoplasic in the first case or homologies [START_REF] Philippe | Phylogenomics revives traditional views on deep animal relationships[END_REF][START_REF] Gazave | No longer Demospongiae: Homoscleromorpha formal nomination as a fourth class of Porifera[END_REF]. Even if the last phylogenomic published data are in favor of the former hypothesis, more biochemical and molecular data are expected to indicate whether or not epithelia emerged before the Eumetazoa. In any case, the first results on O. lobularis suggest that Eumetazoa and Homoscleromorpha use components from a common molecular toolkit to pattern epithelia [START_REF] Lapébie | WNT/beta-catenin signalling and epithelial patterning in the homoscleromorph sponge Oscarella[END_REF]. Data on demosponges also suggest that the principal molecular tools needed to produce epithelial cell cohesion predated epithelial emergence [START_REF] Fahey | Origin of animal epithelia: insights from the sponge genome[END_REF]Srivastava et al. 2010a).

What about stem cell and cell lineage tracking in sponges?

Completing morphogenetic processes also relies on the capacity of the organism to mobilize cells to form a new organization. In other words, morphogenesis depends on the ability of cells to proliferate, migrate, differentiate, dedifferentiate, or even transdifferentiate. For this reason, additional knowledge concerning stem cells, cell lineages, and cell differentiation mechanisms is required to fully understand the morphogenesis in sponges. At present, the expression of so-called stem cellspecific genes has confirmed that the archeocyte are the stem cells in the demosponge Ephydatia. In addition, choanocytes, though they are specialized cells, seem to conserve pluripotency throughout their life [START_REF] Funayama | The stem cell system in demosponges: insights into the origin of somatic stem cells[END_REF][START_REF] Funayama | Piwi expression in archeocytes and choanocytes in demosponges: insights into the stem cell system in demosponges[END_REF]. Is there a pluripotency equivalent? Are stem cells the same in the different sponge lineages? Further data are needed to answer these questions. Nevertheless, in the genus Oscarella where archaeocytes are lacking, we can expect different mechanisms, perhaps relying mainly on transdifferentiation. In order to understand which cells play the role of stem cells and how and to what extent differentiation (or apoptotic) mechanisms are involved in sponge metamorphosis, it is crucial that we develop techniques allowing the study of cells during these processes.

Can these studies help to shed light on sponge gastrulation?

We previously emphasized that both epithelial and epithelial-like as well as mesenchymal morphogeneses occur during poriferan ontogenesis, even when they lack true epithelia (with the exception of Homoscleromorpha). According to comparative embryological data on Porifera and Cnidaria, it is clear that the last common ancestor of the Metazoa (Urmetazoa) was already able to form epitheliallike layers and to disaggregate these layers into individual cells. It was also capable of epithelial-like morphogenesis, i.e., possessed mechanisms ensuring formation of various invaginations and evaginations of the cell layer such as that occurring during gastrulation.

The existence of gastrulation and its identification in sponges has long been problematic and open to debate. Indeed depending on the definition used, researchers have argued either in favor of or against the existence of a gastrulation stage during sponge development and even disagree about which stage should be regarded as a gastrulation (see [START_REF] Leys | Gastrulation in sponges[END_REF][START_REF] Ereskovsky | The problem of germ layers in sponges (Porifera) and some issues concerning early metazoan evolution[END_REF][START_REF] Ereskovsky | Sponge embryology: the past, the present and the future[END_REF]. We have already explained ("Reproduction and development in sponges" section) that the difficulty of determining clear developmental stages in sponges is mainly due to the simultaneity of various cellular mechanisms. For example, morphogenetic movements of single cells or their layers during embryogenesis in sponges are not directly associated with cytodifferentiation: they may precede differentiation of larval cells, coincide with it, or they may follow it [START_REF] Ereskovsky | The problem of germ layers in sponges (Porifera) and some issues concerning early metazoan evolution[END_REF]. The only case where cell differentiation predates morphogenetic movements in sponges is epithelial morphogenesis.

We can expect that exploring more deeply the cellular and molecular mechanisms involved in sponge morphogenetic processes should help us to answer this question more clearly. Thus, because Homoscleromorpha is a unique sponge group with a true epithelial cell layer [named "epitheliosponges" (Ereskovsky and Tokina 2007)] and that epithelial morphogenesis is the main process used throughout homoscleromorph sponges' lafespan [START_REF] Ereskovsky | The comparative embryology of sponges[END_REF], this sponge group appears to be the best candidate to explore the formation and evolution of layers ontogeny.

Thus, the accumulation of cellular and molecular data involved in morphogenesis of homoscleromorphs and comparing them with both other sponge lineages and Eumetazoa should provide important information regarding the origin and early evolution of gastrulation and cell layers in animals.

Fig. 1

 1 Fig. 1 Phylogenetic relationships between the four lineages of Porifera. a Proposed by Philippe et al. (2009). Another recent phylogenomic study (b) favors the paraphyly of sponges (Sperling et al. 2009); for this reason, these relationships were indicated with dashed lines

Fig. 4

 4 Fig. 4 Events during which epithelial cells are transformed into mesenchymal cells and vice versa. The different stages during EMT (epithelial-mesenchymal transition) and the reverse process MET (mesenchymal-epithelial transition) are regulated by effectors of EMT and MET, which influence each other. Important events during the progression of EMT and MET, including the regulation of the tight

Fig. 5

 5 Fig. 5 Developing choanocyte chambers in the pupa of Halisarca dujardini (a SEM, b TEM). a Choanoblasts (chb) with flagella (f) and microvilli (arrows). b Local aggregate of the choanoblasts with the microvilli (mv). f flagellum, mv microvilli, n nucleus. (a and b after: Gonobobleva and Ereskovsky 2004b, reproduced by permission of l'Institut Royal des Sciences Naturelles de Belgique). Scale bars (a, b), 5 μm

Fig. 7

 7 Fig. 7 Diagram of the different paths of formation of the rhagon during metamorphosis of Plakina trilopha. B First stage of metamorphosis. C, C 1 , D, D 1 Second stage of metamorphosis. E, E 1 Third stage of metamorphosis. A Cinctoblastula. B Attachment to substrate. C-E

Fig. 8

 8 Fig. 8 Scheme of Sycon stomoblastula inversion. a Stomoblastula, beginning of placentar membrane development from the accessory cells complex (arrows). b Early and middle (c) stages of inversion, accompanying by placentar membrane growth (arrows). d End of

Fig. 9

 9 Fig.9Origins of non-TALE class and subclass founders on phylogenetic hypothesis according[START_REF] Ryan | The homeodomain complement of the ctenophore Mnemiopsis leidyi suggests that Ctenophora and Porifera diverged prior to the ParaHoxozoa[END_REF]. All the results obtained in sponges reveal that first diversification events of non-TALE gene have occurred before metazoan radiation and a second after the Poriferan-Eumetazoan divergence

Fig. 11

 11 Fig. 11 Origin and evolution of Wnt signaling pathway according to the scenario proposed by Adamska et al. (2010). Each color represents evolutionary origin of each component. Dashed lines indicated absence of specific protein-protein binding motif

Author's personal copy

Dev Genes Evol (2013) 223:5-22

Dev GenesEvol (2013) 223:5-22

Acknowledgements This study was partly funded by an RFBR grant (grant no. 09-04-00337) and by a PICS-RFBR grant (grant no. 5581 and 10-04-91053). The English language has been revised by Thomas Smith.

Author's personal copy

Author's personal copy


Julian Warner
email: j.warner@qub.ac.uk

Fidelia Ibekwe-Sanjuan
email: fidelia.ibekwe-sanjuan@univ-amu.fr

Isabella Peters
email: i.peters@zbw.eu

Niels Windfeld Lund

Michael Buckland
email: buckland@ischool.berkeley.edu

Tomato tomahto: European perspectives on information science

Keywords: History of information science, Cultural variation in information science, Europe, Globalization, ASIS&T

.

In the lyric, 'tomato tomahto', the marked, or explicitly differentiated term, is tomahto, corresponding more to the English rather than the United States pronunciation.

The marked term of a contrast characteristically designates the exception or minor term and the distinctions contained in the unmarked term may be implicitly, and incompletely, understood. Analogously, information science has often been implicitly based in the United States and influenced by American modes of thought, while European, including English, developments have been the occasionally marked and often minor term. This panel explores European perspectives on information science, explicitly and implicitly contrasting them with United States perspectives, from a base in a number of languages and in Europe and beyond.

The panel employs diverse and complementary viewpoints and should make for a lively discussion. It concludes, in sympathy with Gershwin, that cooperation and integration, corresponding to increasing globalization, is the way forward.

The combination of European and beyond and United States perspectives on information science is especially appropriate for the first ASIS&T Annual Meeting outside North America.

Since the early 1970ties there has been a lot of research in the LIS community in the Nordic countries, characterized with a high degree of contest among the members of the community with much discussion and paradigmatic fights.

The paper will look at:

• Nordic discussions on "what is the core of LIS?". Is it culture, libraries or information -Bourdieu -Wersig -Belkin ?

•

The different paradigms in the Nordic countries: Culture -Information -Institution -document -the clash between the cognitive and the cultural paradigmsdiscussions on where LIS belong in the Academic world, in natural sciences (cognitivists), in humanities (culturalists) or in the social sciences with the institutionalists or in all 3 scientific worlds with the documentation paradigm.

•

Paradigmatic changes in Nordic LIS educationthe scientific clashes had a decisive impact on the Educational programs, in Denmark in the '80ties, moving from 2 distinct educations for respectively Public librarians (Culture) and Academic Librarians (information) to a unified education with information as the hegemonic concept covering the whole library world, and changes in the '90ties with documentation studies in Norway opting for a complementary approach, and a media turn in the 2000ies.

•

Collaboration / inspiration across continents: Nordic region -North America -Nordic Research schools, international journals, international conferences, DOCAM a Norway-US collaboration project.

Julian Warner. The whole earth girded by telegraph cables: European influences on information science.

In the late 19th century, the European thinker, Karl Marx, observed 'the last fifty years have brought a revolution that is comparable only with the industrial revolution of the second half of the last century … the whole earth has been girded by telegraph cables.' (Marx, 1981, p.164) The technology of the technology of the telegraph, fully realized in working form in the mid-19th century as the transcontinental (United States) and transatlantic telegraph, was later theoretically described by the model of communication given in Claude Shannon's 'A mathematical theory of communication' [START_REF] Shannon | A mathematical theory of communication[END_REF][START_REF] Shannon | A mathematical theory of communication[END_REF]. This presentation traces some diverse European influences on and contrasts with United States theory and practice in central to information science. First, the working telegraph is understood as a product of the westward expansion of the United States and the increasing links with Europe and the corresponding need for message transmission technologies. The influence of the working telegraph on [START_REF] Shannon | A mathematical theory of communication[END_REF][START_REF] Shannon | A mathematical theory of communication[END_REF]) rigorous account of communication and Warren [START_REF] Weaver | Recent contributions to the mathematical theory of communication[END_REF] more expansive interpretation of that account is investigated. Secondly, we trace Norbert Wiener's indebtedness to European thinkers such as Marx for his understanding of technology as a cumulative human construction -'In all engineering, there is a certain family history, a certain genealogy. The smith's hammers were forged by the hammers of an earlier smith' (Wiener, 1993, pp.46-47) and for his conception of developments in information and communication technologies as a second industrial revolution. Thirdly, the contrast between the United States and the European Union in their treatment of intellectual property in databases, with the United States retaining the integrity and scope of copyright (Feist, 1991) and the European Union developing sui generis provisions for databases is considered. In this instance, the United States, a more recent formation than many European countries, may have had a greater and more extensive historical sense.

The presentation concludes by pointing to the value of a fully theoretical informed, ecumenical but controlled, framework for understanding information developments.

Fidelia

Ibekwe-SanJuan. Information and Communication Sciences in France: the balancing act.

Although Belgium and France can be said to be the cradle of Library Science and Documentation with Paul Otlet's Traité de la Documentation (1934), his monumental work on universal bibliographic classification and dissemination system and Suzanne's Briet's Qu'est-ce que la documentation? (1950), Information Science has not known a "felicitous" evolution in many European countries. Despite providing the founding works upon which Library and Information Science took root and spread to other parts of the world (notably well developed in the US), Information Science has failed to coalesce in Europe into a solid body of well-identified academic discipline with its core theories, paradigms and methods. Instead, it appears to have been merged into other social sciences and humanities fields. The situation is very disparate in every European country and it is difficult to get a global view. For instance, the phenomenon of iSchools is a North American thing. France's situation vis-à-vis Information is peculiar since the discipline or field is not autonomous but is merged into a composite discipline called Information and Communication Sciences (ICS). We have recalled in earlier panels and publications the historical contexts and epistemological underpinnings of this fusion of IS into one composite interdisciplinary field. In this panel, we will focus on how the marriage with Communication and media studies has shaped the types of theories, methodologies and terminology adopted by Information scientists in France. For instance, the concepts of "info(r)communication" and of "info(r)communicational devices" have been coined over the last decade within the ICS in France to attempt to better link the two concepts and therefore the two communities but also more importantly, in a bid to highlight the fact that information without communication is not an operative concept within the discipline. Information is mostly viewed as a human phenomenon involving communication or media. When taken separately, information is attributed to Computer science. Current IS studies in France seem to be distancing themselves from the quantitative and empiricist approaches which characterized research in the first two decades of the existence of ICS field (roughly between 1980-2000). There is a clear shift towards a more human and cultural focus in research which in turn solicits qualitative and comprehensive methodologies.

Michael Buckland. A (Mostly) European Influence on Information Science: Documentation and Neodocumentalism.

The influences and terminology in the development of Information Science are far too complex, ill-defined, and unstable to permit a simple tidy explanation. However, one strand of early twentieth "Documentation" and its later revival and development in the work of Niels Lund, the Document Academy and others constitutes a (largely) European contribution. Three phases will be noted:

1.

Classical Documentation: Paul Otlet and others sought ambitiously to expand bibliographical access through using the newest technology (cards, the Universal Decimal Classification, and potentially much more). To differentiate their form of bibliography from other uses of the word, they eventually adopted Documentation as the term of choice. Suzanne Briet refined and developed Otlet's theorizing for mid-20th century conditions.

2.

Watson Davis and, later, Jesse Shera picked up on European Documentation and promoted it, but in limited ways. Davis, the principal founder of ASIS&T (as the American Documentation Institute) in 1937, seems to have been primarily interested in technical aspects, especially microfilm. Shera promoted, by republishing with an introduction, the book Documentation by the British librarian, Samuel Bradford's book, but failed to understand Briet's ideas.

3.

The U.S. zoologist Herbert H. Field developed a service essentially similar to Otlet's in parallel (also starting in 1895) through the Concilium Bibliographicum, but based in Switzerland.

4.

Mutual influences are hard to discern and probably masked by the far stronger development of special libraries in the U.S. when largely absent in Europe.

5.

Independently (at first) in Europe and in the USA in the 1990s led to a "neo-documentalist" revival of interest in a "document-centric" perspectives in Information Science.

Neo-documentalist influences include an emphasis on "document-as-thing," an expansive, inclusive view of what might be considered a document, and an insistence the necessary and co-existing presence of physical, social, and mental aspects in any adequate discussion of Information Science. These trends appear to have been widely influenced Information Science and seem likely to do so increasingly.

Isabella Peters. Definitions and perceptions of information science -as provided by members of the ASIS&T European Chapter.

In the paper the members of ASIS&T's European Chapter will be given a voice. It will be reported how they define and perceive the concept 'information science' from their particular point of view and specific background. Descriptions and definitions will be categorized and major as well as outstanding viewpoints will be presented. This will provide a map of concepts related to 'information science' and will provide a 'visual' starting point for discussion during the panel.

Currently, the more than 115 members of the European Chapter come from more than 20 different countries and are affiliated with universities, research institutions, other information service providers, and other institutions and enterprise. Also, the members reflect the entire range of levels of professionality, from PhD students to more senior researchers.

Moreover, the student division of the European Chapter will also contribute its view and a long with it provide details on how people rather new in field understand 'information science'.

Julian Warner is a faculty member at the Queen's University Management School, Belfast, Northern Ireland, where he teaches courses in the human aspects of modern information and communication technologies and in information policy. He has been a visiting scholar at the Universities of California at Berkeley, Illinois, Indiana, and Edinburgh. He has research interests in creativity for copyright, information retrieval, and in information technology and the mechanization of mental labor. He has published a number of journal articles in information science and four books, the first of which was translated into Japanese. Isabella Peters is Professor for Web Science at ZBW Leibniz Information Centre for Economics and Kiel University, Kiel, Germany. Currently she is the chair of ASIS&T's European Chapter and researches user-generated content and social media and their use in knowledge representation, information retrieval, evaluation of science (i.e. altmetrics), and open science.