Control of organ formation and morphogenesis during development

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The long-term goal of my research program is to understand how groups of cells develop into specialized adult organs. Such a process requires regulation of growth, morphogenesis and differentiation. My group has focused primarily on the fruit fly eye to investigate numerous aspects of cell signaling that drive tissue specification. We now turn our attention to the events that occur after cell signaling and regulation of gene expression has occurred. Specifically, we are interested in the mechanical and structural changes that lead to the formation of the final three-dimensional organ. The insights we gain are likely to be broadly applicable to understanding how an undifferentiated epithelium develops into a specialized adult organ. My lab uses the well-characterized, genetically-tractable fruit fly Drosophila as a model organism to understand how cellular events are regulated during eye formation. Adult tissues are patterned during larval stages in discrete sacs of epithelial cells called imaginal discs. The adult eye arises from the eye disc and comprises an ordered array of unit eyes. Eye development initiates at the posterior edge of the disc and moves anteriorly in a virtual "wave" of differentiation known as the morphogenetic furrow (MF). The MF is seen as a narrow band of cells constricting both apically and apico-basally which causes them to appear as a physical groove in the epithelium. Cells anterior to the MF exist in an undifferentiated proliferative state, while those behind the MF undergo morphogenesis and differentiation. Thus the MF represents the transition point between cell division and subsequent retinal differentiation. The pace of the MF is tightly regulated to ensure the proper balance between these two opposing cellular states. To date, few studies have addressed the role of the profound cellular shape changes that occur during MF progression, and little is known about how morphogenesis influences differentiation, although they have been proposed to be tightly linked. We will address these issues through researching the following short-term objectives over the next 5 years: Objective 1. Determine the role and mechanism of the Ste20 kinase family member Misshapen (Msn) in regulating MF progression. Recently we found a novel role for the Ste20 kinase Msn as a negative regulator of MF progression. Loss of msn leads to altered cell morphology. Ste20 kinases have diverse roles, and we propose that Msn’s putative role as a regulator of integrins is central to its ability to regulate the MF. We will determine how Msn regulates integrin stability, localization and activity through immunofluorescence, genetic interactions studies and biochemical assays. Further, we will investigate regulation of microtubules, myosin and actin by Msn, using similar multi-facetted approaches. Objective 2: Characterize the expression, localization and function of cell-extracellular matrix (ECM) adhesion associated components during larval eye development. To date, our understanding of MF progression in the eye has been largely restricted to apical cell surfaces and to cell-cell adhesion. We aim to determine the role of cytoskeletal players at the basal cell surface and the relative contribution of cell-ECM adhesion during this dynamic process. Given the critical roles identified for adhesion and cytoskeletal remodeling in other morphogenetic contexts, we hypothesize a similar but as yet unrecognized contribution to MF progression. We will perform an in depth analysis of the expression and localization of ECM and cytoskeletal components during eye morphogenesis. We will use genetic analyses to determine the relative functional requirements for integrin subunits in recruiting ECM factors, as well as in promoting cell differentiation.