Defining the mechanisms that remodel the multivalent domain structures of cell junctions during morphogenetic activities

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In my project I will gain further understanding how cells remain attached to each other during morphogenetic processes in which the junctional complexes have to respond dynamically to cell shape changes and mitotic activity. A failure of this process can lead to developmental disorders and metastasis of cancer cells. I hypothesize that this dynamic response is based on the structure of the junctional complex with multivalent domains that regulate the connection of junctions to the cytoskeleton. In this study, I will further investigate the role of the junction-associated proteins Pyd and Cno in embryonal epithelial tissues of Drosophila melanogaster. The processes of germ band elongation and dorsal closure during Drosophila embryogenesis provide a useful tool to investigate junctional dynamics as they are defined by high tissue forces due to cell intercalation, mitosis and tissue movement. In cno and pyd mutant embryos, tissue rupture and perturbed cell shapes were especially observed at regions with elevated tissue stress. Thus, these proteins seem to provide robustness to adherens junctions by being able to connect the junctional complex to the cytoskeleton. However, their mechanistical role in this process remained unclear. I will analyze the effect of Pyd on junction robustness by detailed examination of mutant phenotypes and investigate the roles of known Pyd interactors in this process. Preliminary data could confirm perturbed cell shapes in pyd mutants during the process of germ band elongation that could be a result of perturbed cell intercalation and junction dynamics. Further investigation of fixed and live specimen will include detailed description and quantification of cell shapes, cell intercalation and junction dynamics which will help to understand the function of these junction-associated proteins.The fact that cells within a tissue are dynamic requires dynamic junctions which have to ensure integrity during mitosis, cell intercalation and cell shape changes. Thus, the stable cell-cell junction should on the one hand provide stiffness but on the other hand respond flexible on changes. Thus, I hypothesize that the junctional complex and its connection to the cytoskeleton display a substructure of interacting proteins that provide the ability to provide both requirements. Primary indication of a potential substructure is the partial segregation of the junction-associated proteins Arm, Cno and Baz in mature Drosophila epithelia. During my study, I will further dissect the substructure of cell junctions in Drosophila embryos and mammalian cells by super-resolution microscopy. In both systems will study junction dynamics during their maturation and maintenance. Furthermore, I will compare the substructures of junctions within one tissue that exhibit differential forces, f. e. tricellular junctions with higher forces versus bicellular junctions.