Normal embryonic development requires a precise coordination of cell divisions, inductive events and gastrulation cell movements that establish the body plan with organ rudiments. Several signaling pathways have been shown to control vertebrate embryogenesis, including canonical and non-canonical- Wnt, BMP, FGF, Hh, and Notch. Mutations in the components of these pathways cause miscarriages, birth defects and diseases, including cancer, underscoring the significance of studies of embryogenesis. Although G protein-coupled receptors (GPCRs) constitute the largest family of signaling receptors that regulate immune and nervous system development and function, they have not been considered as regulators of early embryonic development. In the previous funding period of this project, we, as well as other groups, uncovered key roles of several GPCRs and heterotrimeric G protein signaling in gastrulation, heart formation and myelination. Motivated by these findings, we identified and analyzed the expression of 32 zebrafish genes encoding chemokine GPCRs and discovered that more than half of them are expressed, and several have unexpected roles, during embryogenesis. To uncover the contribution of chemokine GPCRs to vertebrate development, our Aim 1 is to interrogate functions of the subset of 21 chemokine GPCRs expressed during embryogenesis by generating loss-of-function mutations in these genes in zebrafish and determining the consequences on cell fate specification and movements.
In Aim 2, we will test the hypothesis that Ccr7 chemokine GPCR regulates axis formation by inhibiting ?-catenin in a GSK3? independent and a G?q/Ca2+/Naked1- dependent pathway. We will define ligands that regulate Ccr7 activity during axis formation and test whether Ccr7 cooperates with Cxcr3 chemokine GPCR and non-canonical Wn5a signaling in this process.
Our Aim 3 is to test the hypothesis that the function of Ccr7 GPCR as a negative regulator of ?-catenin is conserved in human cells. We will also assess its tumor-suppressing activity in zebrafish and mouse by testing whether ccr7 mutations increase tumor formation when combined with mutations in Adenomous polyposis coli, a key tumor suppressor and ?-catenin inhibitor. Our functional survey of the chemokine GPCRs in zebrafish can define new roles of these receptors in various aspects of vertebrate development. We will determine whether Ccr7 acts as an evolutionarily conserved negative regulator of ?-catenin in human cancer cells and a tumor suppressor in zebrafish and mouse. Taking advantage of a powerful vertebrate genetic system, these studies can establish chemokine GPCRs as candidates (and potential drug targets) for human birth defects and diseases.
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