Morphogenesis: Biophysics and Genetics of Dorsal Closure

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DESCRIPTION (provided by applicant): Drosophila's Dorsal Closure is a model system for cell sheet morphogenesis during development and wound healing. We plan to investigate the molecular, cellular, and emergent properties that drive morphogenesis during closure using biophysical (laser microsurgery), genetic, pharmacological and modeling approaches. Previously, we showed that nonmuscle myosin II drives contractility in the amnioserosa and in the supracellular, actomyosin-rich purse-strings and that both tissues drive the bulk of progress toward closure. In addition we showed that the tissue forces are coordinated by adhesion- mediated zipping, that there is an asymmetry between the anterior and posterior zipping rate constants, and that the zipping rate constant can be upregulated in response to laser perturbation. We also showed that the removal of one or another force leads to upregulation of the forces that remain and closure proceeds to completion at wild type rates. Furthermore, the upregulation of the amnioserosa force and the zipping rate constant together address the robustness and resiliency of closure. Finally, we showed that the vector sum of the forces that drive closure is two to three orders of magnitude smaller than the individual forces that contribute. This indicates that regulation of these large forces is required so that cell sheets move inexorably to closure. Here we focus on applying laser-surgical, pharmacological and quantitative-modeling tools to explore the emergent properties that are the consequence of the cellular and molecular machines that drive cell sheet morphogenesis in wild type and mutant animals. By applying these methods to the analysis of wild type embryos an selected mutant embryos that fail in on or another aspect of closure, we plan the following. 1) We will investigate the hypotheses that mechanically gated channels and/or cell-matrix and cell-cell junctions sense and respond to forces to regulate the rate of closure. 2) We will measure the absolute magnitude of the forces each tissue contributes to closure. 3)We will investigate the role of microtubules in regulating actin function for closure. 4) We will formulate mathematical models that recapitulate at tissue and/or cellular resolution the behavior of closure in mutant, pharmacologically perturbed or laser investigated embryos. These studies on cell sheet morphogenesis in Drosophila will provide insight into the cellular and molecular basis for the biological processes that coordinate cell shape changes in vertebrate morphogenesis and wound healing. PUBLIC HEALTH RELEVANCE This work focuses on dorsal closure, a process in the fruit fly Drosophila melanogaster that models cell sheet movements in vertebrates. Drosophila offers unique opportunities for multidisciplinary approaches and many of the proteins involved in movement are highly conserved between flies and humans (some are > 90% identical and many human proteins can experimentally rescue genetic defects in their fly orthologs). In addition, comparable sheet movements characterize early stages of human development (for example, neural tube formation) and wound healing. Moreover, the programmed interplay between cell-cell junctions and cell-matrix junctions that occurs during closure is crucial for the epidermal-mesenchymal transition that is activated when epithelial cells become metastatic and cause cancer. These studies in Drosophila will provide insight into the molecular and cellular basis of motility and provide a window onto the emergent behaviors that characterize morphogenesis and wound healing.