JCJC - Jeunes chercheuses & jeunes chercheurs

Identification of novel genes required for follicular cell development in the Drosophila ovary – morphoepithe

Submission summary

The epithelium forms a vital part of all our tissues and organs. The adhesive properties of these cellular sheets and the ability of their component cells to change shape or to move are essential to generate the large number of tissues and organs that can be found in a multicellular organism. Consequently, abnormal differentiations or behaviours of epithelial cells can induce cancers or other human pathologies. It is therefore essential to increase our understanding of the fundamental biological processes of cellular differentiation, adhesion and migration in epithelial cells. The general context of my research is part of the following question: what are the cellular and molecular mechanisms that link epithelial cell differentiation and the underlying morphogenetic processes? Drosophila oogenesis provides an elegant context in which to study epithelial processes such as differentiation, change of form, displacement and migration, since they can be observed in the course of the development of a single follicle. The aim of this proposal is the identification of novel genes that function during or after follicular cell differentiation to modify the adhesion of the cells and their ability to move. To isolate such genes, I plan to use a non-biased strategy by assaying the effects of EMS-mutagenised loci within somatic clones generated in Drosophila female pupae. The methods used to identify gene function will fully exploit the powerful genetic and molecular tools available in Drosophila and a newly developed cellular imaging technique to look at morphogenetic processes in ex vivo follicles. Over the last few years, I have been characterizing the novel roles of previously identified genes in follicle development, such as the genes of the Notch pathway. In particular, I have developed two aspects. The first aspect concerns the role of this pathway during polar cells formation, which is crucial for follicle formation. The second aspect is to study the role of this pathway for the differentiation of the cells involved in the morphogenetic processes that occur during the maturation of the follicle. The results from this latter analysis demonstrate without any ambiguity for the first time that the N pathway controls cellular adhesion by regulating the dynamics of adherens junction remodelling and not cell differentiation. This novel and unexpected result constitutes an important step in our understanding of these morphogenetic processes since it demonstrates that the activity of molecules involved in such processes is linked to the activation of a pathway mainly known to be required for differentiation. This study is now being pursued by analyses of candidate genes identified from the bibliography or from two enhancer-trap lines that present a very specific pattern of expression. However, since only a few such oogenesis-specific lines exist, the identification of genes with a role in oogenesis requires the more general approach of genetic screening of chemically mutagenised Drosophila. The phenotypes will be screened in somatic mutant clones generated in pupae. This will allow the identification of genes required specifically in oogenesis as well as those that, due to their essential roles in early development, would normally not have been identified as having a role in oogenesis. Interesting mutations should lead to abnormal follicle formation or asynchronous morphogenetic processes during follicle maturation. The presence of mutant phenotypes will be detected via the patterns two GFP protein fusions that mark the adherens junctions and the oocyte. I have used the fng mutation to define and optimize the experimental conditions required to perform this complex screen. I plan to analyze the progeny of 8000 individual mutagenised males per arm of chromosome. The resulting loci of interest, already mapped to a chromosome arm due to the nature of the screen, will be fine-mapped using chromosomes bearing multiple visible mutations or bearing small deficiencies available from the DrosDel project and Exelixis, or by analyzing the SNP profiles. The role of identified genes will be then studied by manipulating their expression in vivo in a cell- and stage-specific manner. Finally, the recent development of a technique allowing real-time observation and imaging of live follicles should allow us to assay some of these morphogenetic processes and help us understand the chronological progression of certain key events underlying follicular cell differentiation, adhesion and migration and the role of genes involved in such processes.

Project coordination

Muriel GRAMMONT (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 199,000 euros
Beginning and duration of the scientific project: - 48 Months

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