Characterizing the fundamental mechanisms of epithelial invagination during ocular morphogenesis

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Project Summary Generation of the eye, more so than many organs, requires precise control of its shape for optimal function. Obtaining knowledge of how the eye and lens is constructed during embryonic development is therefore important to help describe the nature of ocular abnormalities that lead to major structural defects or more subtle changes that alter vision. An example of a morphogenetic event required for the generation of organs is epithelial invagination. This process drives the inward bending of epithelia of several early organ systems including that of the lens placode during early ocular development. Although several mechanisms have been proposed to drive this process, such as apical constriction or local placodal growth, none have been found sufficient to account for epithelial bending. We have recently observed that placodal cells change shape, move, and generate cytoskeletal structures in a planar polarized manner that produces a net flow of cells toward the central placode. One of the hallmarks of planar-polarized cell movements such as these is the formation and resolution of cellular rosettes, an organized process of cell rearrangement that requires spatial restriction of junctional proteins that contract and shorten junctions and proteins that lengthen and stabilize cellular junctions. We have identified planar-polarized localization of proteins responsible for junctional contraction (Shroom3 and p120-catenin) and stabilization (Par3 and cdc42). These results led us to our central hypothesis that invagination is driven by a combination of epithelial cell movements and anisotropic cell shape changes organized by radial planar polarized protein localization, junction contraction, and junction elongation. We will test this central hypothesis with three aims utilizing live-fluorescent microscopy of genetically altered mouse embryos. In aim 1 we will characterize the role of anisotropic junctional contraction and analyze the consequences of combined deficiency of Shroom3 and p120 catenin. The goal of aim 2 is to characterize the role of Par3 in junction elongation during rosette resolution and invagination. Aim 3 will investigate whether anisotropic cell geometry and movement results from the mutual antagonism between proteins that induce junctional contraction and junctional elongation. Once completed, the experiments in this proposal will define the cell behaviors that drive the mechanisms of lens placode invagination.