GPCR signaling during embryonic organ formation

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G-protein coupled receptors (GPCRs) are critical for almost every aspect of animal life. These proteins are embedded in the cell membrane and allow us to sense and respond to light, smells, and taste. GPCRs also control responses in both our central and autonomic nervous systems, and they regulate both inflammation and immunity. GPCRs control cell migration for normal development and during cancer metastasis. Indeed, approximately 34% of FDA-approved drugs target GPCRs. Nonetheless, despite decades of study, many GPCRs have no known function, their ligands remain unidentified, and the pathways through which they elicit distinct cellular responses remain mostly uncharacterized. Here, we propose to take the first steps toward understanding the roles of GPCRs during development in the experimental system of the Drosophila embryo, which has numerous advantages in terms of visual accessibility, an extensive armamentarium of genetic tools, and relatively low cost. We begin with an analysis of the Drosophila GPCR Tre1, which has been implicated in germ cell (GC) navigation and survival, extravasation of immune cell to sites of injury, and polarization of neuroblasts. We have recently reported that non-canonical Hedgehog signaling works through the Tre1 receptor to control GC navigation, resolving a long-standing conflict regarding the role of Hh in this process and revealing a novel pathway downstream of Tre1 activation. In the first aim, we uncover the molecular and cellular mechanisms through which each step of this pathway is mediated – from receptor binding to actin polymerization. We ask if and how other genes that affect GC migration work through this pathway to repel GCs (in the case of the Wunen lipid phosphate phosphatases) or attract GCs (in the case of HMGCoA reductase). Tre1 is also expressed in the forming salivary gland (SG), a tissue that, unlike GCs, migrates as a fully polarized epithelial collective. We ask if Hh signaling and Tre1 also function in the SG for its navigation and we ask if Tre1 function in this tissue complements or antagonizes the function of another GPCR – Mthl5 – which is expressed in the SG at about the same time and that has also been implicated in Hh signaling. Finally, we establish a pipeline to screen all of the GPCRs encoded in the Drosophila genome and expressed in embryos for roles in the development of either GCs or the SG. Our pilot screen has already identified two GPCRs with phenotypes consistent with important functions, one gene with a potential role in GC survival and the other with a potential role in regulating the SG extracellular matrix.