Les premières étapes de l’évolution animale restent obscures mais peuvent toutefois être appréhendées par l’étude comparative du développement des animaux basaux comme les éponges, les cnidaires ou les cténophores. Une des innovations majeures dans l’évolution des formes animales est l’apparition de l’épithélium, classiquement considérée comme une synapomorphie des eumétazoaires. Les homoscléromorphes sont les seules éponges à partager avec Eumetazoa la présence d’un véritable épithélium avec notamment une membrane basale contenant du collagène de type IV. Dans ce clade, la recherche des mécanismes épithéliaux sous-tendant le développement a pour enjeu la meilleure compréhension de leur origine et de leur importance dans l’évolution animale. Le travail de cette thèse a consisté à caractériser chez Oscarella lobularis des outils moléculaires responsables des morphogenèses épithéliales. Trois d’entre eux ont été étudiés chez l’adulte. Le premier, la voie WNT canonique, est capable d’induire l’invagination de l’épithélium externe de l’éponge, ce qui n’est pas sans rappeler ce même rôle dans d’autres contextes épithéliaux d’eumétazoaires. Le deuxième est la voie WNT non canonique ou « voie PCP », qui, quand elle est bloquée, empêche l’invagination initiée par la voie canonique. Enfin, le troisième outil est un membre de la famille des gènes à boîte T, OlTbx qui s’exprime spécifiquement dans l’épithélium après l’invagination sus-mentionnée. Cette expression rappelle des expressions d’autres gènes Tbx dans le feuillet endomésodermique invaginé lors de la gastrulation des eumétazoaires. L’invagination semble utiliser une partie d’un même programme génétique dans la gastrula des Eumetazoa et dans l’adulte des Homoscleromorpha. Mes résultats ouvrent des perspectives intéressantes concernant l’éventuelle reconnaissance d’un stade gastrula chez les éponges, point de discorde de la zoologie classique. / The first steps of animal evolution remain obscure but, nevertheless can be better understood by comparative studies of the most basally branching animals, such as sponges, cnidarians and ctenophores. Epithelium is one of the major innovations in the evolution of animal forms and is generally considered as one of the synapomorphies of Eumetazoa. The homoscleromorphs are the only sponges, with Eumetazoa, to have a true epithelium with a basal membrane containing type IV collagen. In this clade, the investigation of epithelial processes underlying development would give insights into their origin and their importance in animal evolution. The aim of my work was to characterize molecular tools involved in epithelial morphogenesis in Oscarella lobularis. I was able to characterize three of those molecular tools. The first one is the canonical WNT pathway inducing invagination of the external epithelium of the sponge, reminiscent of the same function in other epithelial contexts in Eumetazoa. The second one is the non-canonical WNT pathway or “PCP pathway” which blocks invagination when it is inhibited. The third one is a member of the T-box genes family, OlTbx, specifically expressed in the epithelial layer formed by the above-mentioned invagination. Similarly, other Tbx genes are expressed in the endomesodermal layer during eumetazoan gastrulation. Invagination processes involved in both eumetazoan gastrula and homoscleromorph adult tissue seem to share a part (WNT/Tbx) of a common genetical program. My results provide new investigation prospects, in order to answer the difficult question of the origin of gastrulation in sponges.

Au cours de gastrulation chez la Drosophile, deux vagues successives de constriction ont lieux au niveau des cellules ventrales menant à l'invagination du mésoderme. La première vague de constriction est stochastique et entraine la constriction de 40% des cellules mesodermales réparties aléatoirement et est contrôlée par le facteur de transcription Snail. La seconde vague de constriction arrive immédiatement après et implique également la constriction des 60% manquant de cellules mésodermales. Cette seconde vague est contrôlée par le facteur de transcription Twist et requière la présence de la protéine sécrétée Fog. L'invagination complète du mésoderme riquière la redistribution de la protéine moteur Myosine II au niveau de l'apex des cellules en cours de constriction. Il a été montré que la mutation de Snail mène à une perte des deux phases de constriction, mais qu'une indentation sur les cellules du mésoderme permet de rétablir la seconde phase de constriction Twist dépendante. Nous avons cherché à étudier les interaction entre les deux phases de constriction, la protéine sécrétée Fog et le moteur moléculaire Myosine II à l'aide d'une simulation numérique. Nous avons également chercher à étudier la corélation entre l'invagination globale du mésoderme et la phosphorylation de la Bêta-Cathenine qui est impliquée dans l'activation de Twist. Nous avons étudier l'invagination de l'endoderme postérieur qui présente de nombreuses similitude avec l'invagination de l'endoderme et leurs interactions. Enfin également à l'aide d'une simulation numérique, nous avons testé l'hypothèse de l'apparition d'une invagination dans un organisme primitif mécano-sensible ( la gastræ d'HAECKEL ) au contact avec le plancher océanique. / During Drosophila gastrulation, two waves of constriction occur in the apical ventral cells, leading to mesoderm invagination. The first constriction wave is a stochastic process mediated by the constriction of 40% of randomly positioned mesodermal cells and is controlled by the transcription factor Snail.The second constriction wave immediately follows and involves the other 60% of the mesodermal cells. The second wave is controlled by the transcription factor Twist and requires the secreted protein Fog. It is known that Snail mutation lead to the loss of the two constriction phases but a mechanical poking on the mesoderm cells can rescue de second phase of Twist dependent constriction. The interactions between the two constriction phases, la secreted protein Fog and the molecular motor Myosin II with a numerical simulation. The posterior endoderm invagination that presents similarities with mesoderm invagination have been study, as well as the interaction between them. Finally with an other numerical simulation, the hypothesis of an induced invagination on a primitive mechanosensible organism ( the HAECKEL grastrae ) on the contact with the oceanic floor has been tested.

Les cellules épithéliales fournissent différentes fonctions biologiques: elles servent de barrière entre l'extérieur et l'intérieur d'un organisme et forment un continuum mécanique à travers les jonctions adhérentes qui les connectent. Au cours du développement, elles subissent des modifications extrêmes pour former l'embryon: elles changent de forme, modifient leur position relative ou perdent leur intégrité épithéliale. La plus part de ces changement se basent sur la modulation de l'actomyosine corticale et jonctionale, et sur la modulation des protéines qui définissent et maintiennent la polarité apico basale. Neuralized (Neur) est une E3 ubiquitine ligase qui est conservée des nématodes jusqu'aux mammifères. Elle a été découverte pour son rôle dans la régulation de la signalisation Delta/Nocth. Dans ce travail on décrit deux autres functions Notch-indépendantes de Neur dans le remodelage des épithéliums. En premier temps, on montre que Neur régule négativement la protéine apicale Crumbs à travers une isoforme de Stardust, ce qui permet le remodelage de l'intestin postérieur de la Drosophile et favorise la migration trans-epithéliale des cellules germinales primordiales. Puis, on présente que, pendant la gastrulation, Neur module la contractilité de l'actomyosine dans le mésoderme, et indirectement dans l'ectoderme, pour contrôler la formation du sillon ventral. / Epithelial cells serve many biological functions: they act as a barrier to separate the interior from the exterior, and form a mechanical continuum through the junctions that interconnect them. During development, they undergo dramatic changes to shape the embryo: they change their shape, modify their relative position or lose their epithelial integrity. Most of these changes rely on the modulation of cortical and junctional actomyosin, and the regulation of the proteins that define and maintain the epithelial apical/basal polarity. Neuralized (Neur) is an E3 ubiquitin ligase conserved from nematodes to mammals. It was first discovered for its role in the regulation of Delta/Notch signalling. Here we describe two Notch independent roles of Neur in epithelial remodelling. First, we show that Neur negatively regulates the apical protein Crumbs though a specific isoform of Stardust. This allows the remodelling of the drosophila posterior midgut and favours the trans-epithelial migration of the primordial germ cells. Finally, we present that Neur modulates actomyosin contractility in the mesoderm, and indirectly in the ectoderm, to control ventral furrow formation during gastrulation.

The aim of this thesis was to investigate morphogenesis in the fruit fly Drosophila melanogaster using three in vitro tissue culture systems. Primary embryonic cultures derived from Drosophila melanogaster were used to study the effect of the moulting hormone ecdysone on cells in culture. The hypothesis was that the effect of ecdysone on these primary embryonic cells would parallel events which occur during metamorphosis in vivo and therefore the primary embryonic cultures could be used as an ‘in vitro’ model system. Transgenic fly lines expressing GFP were used to visualise and identify specific cell types and it was shown that cells in primary embryonic cultures respond to ecdysone morphologically. However due to the variability of cultures it was concluded that this culture system was not suitable for use as a model system. As defined cell types were observed the development of a protocol suitable for use with the primary embryonic culture system using dsRNA in order to demonstrate RNA interference was undertaken. Although this was unsuccessful, as cells in the primary embryonic cultures appeared to be resistant to dsRNA, some technical avenues remain to be explored. The Drosophila melanogaster cell line, Clone 8+, was used to investigate cell adhesion in tissue culture. Statistical analyses were carried out and it was established that derivatives of the parent cell line, Clone 8+, showed differential adhesion and proliferation characteristics. Analysis of microarray data was carried out in order to identify genes which may be responsible for the loss of cell adhesion in Clone 8+ cell lines and the potential roles of these genes in adhesion were discussed. A gene of interest, glutactin, was identified which may be responsible for loss of cell adhesion. Antibody staining was used to establish the expression of the protein glutactin in the Clone 8+ cell lines. The expression of glutactin suggested that the Clone 8+ cell line had maintained properties of the wing disc epithelial cell-type and disruption of cell polarity was considered as a possible mechanism. It was shown that f-actin colocalised with glutactin and the role of the cytoskeleton in glutactin secretion was discussed. It was concluded that glutactin was not responsible for loss of cell adhesion in the Clone 8+ cell lines. Further analysis of the microarray data revealed potential genes that could be responsible for the loss of cell polarity in the Clone 8+ cell lines and the possibility of cellular senescence was considered. It was hypothesised that the properties of adhesion and proliferation related to their ‘in vitro’ age. In the final investigation the movement of epithelial cells in Drosophila melanogaster third instar larval imaginal discs during morphogenesis was investigated. Firstly a lumen was identified in fixed imaginal disc tissue in association with cells expressing f-actin. This result was discussed in relation to the process of dorsal closure and wound healing. Further investigations involved live imaging of the dynamic process of evagination in the imaginal wing disc using transgenic flies expressing moesin-GFP. It was concluded that the lumen was not associated with the process of wound healing and it was concluded that the lumen appeared to be the mechanism directing peripodial epithelium contraction during morphogenesis of the imaginal wing disc. Dorsal closure and the process of invagination in relation to morphogenesis of the imaginal wing disc were discussed.

O cristalino de vertebrados se origina a partir da invaginação do ectoderme que recobre a vesícula óptica. A invaginação epitelial em diversos modelos é causada pela constrição celular apical, mediada pela contração apical de actina e miosina II e regulada pela GTPase RhoA. Neste trabalho nós investigamos se a invaginação do cristalino em embriões de galinha ocorre devido à constrição celular apical e se este evento é controlado por RhoA. Actina filamentosa e miosina II são expressas na porção apical do cristalino durante a invaginação. Quando a polimerização de actina é inibida por Citocalasina D, o cristalino não invagina, sugerindo que a constrição celular apical poderia contribuir para a invaginação do cristalino. RhoA também é expressa durante o desenvolvimento do cristalino, mas a inibição de RhoA, por eletroporação da forma dominante-negativo, não impediu a invaginação do placóide do cristalino, não alterou a distribuição de miosina II na porção apical do cristalino nem sua ativação, indicando que a invaginação do cristalino independe de RhoA. / Vertebrate lens derives from invagination of the ectoderm that overlies optic vesicles. Epithelial invagination in many model systems is driven by apical cell constriction, mediated by actin and myosin II contraction regulated by GTPase RhoA. Here we investigate the possibility that chick lens placode invagination could also be driven by apical cell constriction and controlled by RhoA. We show that actin and myosin II are expressed at lens apical side during lens invagination. Actin polymerization inhibition by in ovo Cytochalasin D treatment prevents lens placode invagination, suggesting that lens placode invagination could be driven by apical cell constriction. RhoA GTPase is also expressed at apical portion of lens placode and during lens invagination. However, when we overexpressed by electroporation the dominant-negative RhoA in the pre-lens ectoderm invagination was not affected. Furthermore, dominant-negative RhoA didnt affect myosin II apical localization nor myosin II phosphorilation, indicating that in lens invagination this process is not regulated by GTPase RhoA.

Les progrès continus de la recherche scientifique dans le domaine de la santé ont entraîné une augmentation de l'espérance et de la qualité de vie. Ainsi, le développement de nouveaux médicaments et des dispositifs médicaux a permis d'améliorer les conditions sanitaires et la prise en charge des patients au prix d'une inflation des dépenses de santé. Ces évolutions ont eu pour conséquences d'inciter les états à mettre en place des procédures d'évaluation de l'efficacité et de la gestion des risques liés à ces nouvelles approches thérapeutiques. Plus récemment, les restrictions budgétaires liées à la crise économique dans de nombreux pays de l'OCDE ont contraint les états à diminuer la part de leur budget consacré à la santé. Cette situation les a conduits à mettre en place des politiques de santé basées sur l'optimisation des ressources.En ce sens, l'évaluation médico-économique et la pharmaco-épidémiologie constituent pour les acteurs de santé et pour les décideurs politiques un outil d'analyse décisionnelle particulièrement légitime. Ils sont aujourd'hui de plus en plus intégrés dans les réflexions sur les stratégies de soins et dans la mise en place des programmes de santé. L'objectif de notre travail de recherche a été à travers deux projets, d'étudier l'intérêt de l'évaluation médico-économique et de la pharmaco-épidémiologie en chirurgie pédiatrique. Ainsi, dans une première partie plus théorique, une synthèse des différentes études de pharmaco-économie, de pharmaco-épidémiologie a été conduite et un état des lieux des études d'évaluation médico-économiques dans la chirurgie de l'enfant a été réalisé. Dans une seconde partie plus pratique, les deux projets concernant la chirurgie pédiatrique sont présentés :- Le projet 1 (pharmaco-économie) présente l'évaluation et l'analyse coût-efficacité dutraitement du reflux vésico-urétéral de grade modéré chez l'enfant.- Le projet 2 (pharmaco-épidémiologie) est une étude multicentrique prospective surl'épidémiologie de l'invagination intestinale aiguë de moins de 1 an (EPIstudy) / The continuing progress of scientific research in the field of health have led to increasingexpectancy and quality of life. Thus, the development of new medicines and medical deviceshave improved the health conditions and treatment of patients at the cost of inflation inhealth spending. These developments have effects for encouraging states to implementprocedures of effectiveness assessment and management of risks associated with these newtherapeutic approaches.More recently, budget cuts due to the economic crisis in many OECD countries havecompelled states to reduce the proportion of their budgets on health. This led them todevelop health policies based on resource optimization.In this sense, the health econoic evaluation and pharmacoepidemiology are for healthcarestakeholders and policy makers a tool for decisional analysis. They are now increasingly integrated into reflection on care strategies and the implementation of health programs. The objective of our research has been through two projects, to study the interest of the health economic evaluations and pharmacoepidemiology in pediatric surgery. Thus, in a first, theoretical part, it is a synthesis of various studies of pharmaco-economics, pharmacoepidemiology was conducted and an inventory of economic evaluation studies in pediatric surgery was performed. In the second part more convenient, both projects are presented in pediatric surgery :- Project 1 (pharmacoeconomic) presents evaluation and cost-effectiveness analysis oftreatment of moderate grade of vesicoureteral reflux in children.- Project 2 (Parmacoepidemiology) is a prospective multicenter study of theepidemiology of acute intussusception among infants (EPIstudy)

O cristalino de vertebrados se origina a partir da invaginação do ectoderme que recobre a vesícula óptica. A invaginação epitelial em diversos modelos é causada pela constrição celular apical, mediada pela contração apical de actina e miosina II e regulada pela GTPase RhoA. Neste trabalho nós investigamos se a invaginação do cristalino em embriões de galinha ocorre devido à constrição celular apical e se este evento é controlado por RhoA. Actina filamentosa e miosina II são expressas na porção apical do cristalino durante a invaginação. Quando a polimerização de actina é inibida por Citocalasina D, o cristalino não invagina, sugerindo que a constrição celular apical poderia contribuir para a invaginação do cristalino. RhoA também é expressa durante o desenvolvimento do cristalino, mas a inibição de RhoA, por eletroporação da forma dominante-negativo, não impediu a invaginação do placóide do cristalino, não alterou a distribuição de miosina II na porção apical do cristalino nem sua ativação, indicando que a invaginação do cristalino independe de RhoA. / Vertebrate lens derives from invagination of the ectoderm that overlies optic vesicles. Epithelial invagination in many model systems is driven by apical cell constriction, mediated by actin and myosin II contraction regulated by GTPase RhoA. Here we investigate the possibility that chick lens placode invagination could also be driven by apical cell constriction and controlled by RhoA. We show that actin and myosin II are expressed at lens apical side during lens invagination. Actin polymerization inhibition by in ovo Cytochalasin D treatment prevents lens placode invagination, suggesting that lens placode invagination could be driven by apical cell constriction. RhoA GTPase is also expressed at apical portion of lens placode and during lens invagination. However, when we overexpressed by electroporation the dominant-negative RhoA in the pre-lens ectoderm invagination was not affected. Furthermore, dominant-negative RhoA didnt affect myosin II apical localization nor myosin II phosphorilation, indicating that in lens invagination this process is not regulated by GTPase RhoA.