Morphogenesis: Biophysics and Genetics of Dorsal Closure

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Cell sheet morphogenesis plays crucial roles in developmental milestones during vertebrate morphogenesis, including gastrulation and the formation of the neural tube, the heart, and the palate. It is also essential for wound healing. Coordination of the cellular machineries and the signaling cascades that drive and regulate morphogenesis is critical – misregulation results in developmental and wound healing defects that can be fatal. We focus on the fundamental biology of how cell sheet morphogenesis is powered, regulated and coordinated during dorsal closure in Drosophila melanogaster. Conservation of molecular, cellular and tissue archictecture make closure an ideal model system for interrogating the molecular basis of morphogenesis. During closure, lateral epidermal sheets advance to close a dorsal opening. Closure is amenable to a wide variety of diverse experimental approaches and we pioneered the study of closure as a model system, especially through the use of live imaging strategies. We identified four processes that contribute to closure and demonstrated that no single force that contributes is absolutely required. Thus, closure is robust, resilient and redundant using molecular components that are conserved across metazoan phylogeny. Our recent work focuses on how ion fluxes contribute to closure and proposes a thermodynamic model to understand tissue remodeling during closure. We address how signals from patterning and polarity gene products converge to regulate cell shape and the changes in cell shape that characterize morphogenesis. We initiated a forward genetic screen that directly assesses the kinematics of closure and investigates the genetic basis for closure's robustness and resilience. More than 140 genes were previously known to contribute to DC and we have already discovered 23 additional genetic intervals that are required for closure in a pilot screen of just ¹/? of the fly genome. During the next five years we plan to use gene discovery to identify new genes that are required for closure. We will use high-resolution 4D imaging to document quantitatively the cellular shape changes that characterize closure in wild type and mutant animals, then use biophysical strategies to determine how these new genes contribute to force production and regulation of closure. Key conceptual gaps we plan to address are what roles embryonic patterning plays in establishing the cellular and subcellular architectures that characterizes the embryo at the onset of closure and how ion fluxes contribute to closure. We will investigate the signal (or signals) that triggers the onset of closure and feedback mechanisms that compensate for genetic or physical insults to the progress of closure. We will continue to explore how force-generating cytoskeletal components are positioned, coordinated and regulated and study how adhesion complexes both transmit forces and allow cell movements. We are uniquely poised to address key extant questions that characterize the basic biology of cell sheet morphogenesis in flies. Because morphogenesis is highly conserved at the molecular, cellular and tissue levels, our work directly informs vertebrate morphogenesis in development and wound healing.