MABN310 Sigma-AldrichAnti-G-protein coupled receptor 56 (GPR56) Antibody, clone H11

Blood formation by hematopoietic stem cells (HSCs) is regulated by a still incompletely defined network of general and HSC-specific regulators. In this study, we analyzed the role of G-protein coupled receptor 56 (Gpr56) as a candidate HSC regulator based on its differential expression in quiescent relative to proliferating HSCs and its common targeting by core HSC regulators. Detailed expression analysis revealed that Gpr56 is abundantly expressed by HSPCs during definitive hematopoiesis in the embryo and in the adult bone marrow, but its levels are reduced substantially as HSPCs differentiate. However, despite enriched expression in HSPCs, Gpr56-deficiency did not impair HSPC maintenance or function during steady-state or myeloablative stress-induced hematopoiesis. Gpr56-deficient HSCs also responded normally to physiological and pharmacological mobilization signals, despite the reported role of this GPCR as a regulator of cell adhesion and migration in neuronal cells. Moreover, Gpr56-deficient bone marrow engrafted with equivalent efficiency as wild-type HSCs in primary recipients; however, their reconstituting ability was reduced when subjected to serial transplantation. These data indicate that although GPR56 is abundantly and selectively expressed by primitive HSPCs, its high level expression is largely dispensable for steady-state and regenerative hematopoiesis.

GPR56, an orphan G protein-coupled receptor (GPCR) from the family of adhesion GPCRs, plays an indispensable role in cortical development and lamination. Mutations in the GPR56 gene cause a malformed cerebral cortex in both humans and mice that resembles cobblestone lissencephaly, which is characterized by overmigration of neurons beyond the pial basement membrane. However, the molecular mechanisms through which GPR56 regulates cortical development remain elusive due to the unknown status of its ligand. Here we identify collagen, type III, alpha-1 (gene symbol Col3a1) as the ligand of GPR56 through an in vitro biotinylation/proteomics approach. Further studies demonstrated that Col3a1 null mutant mice exhibit overmigration of neurons beyond the pial basement membrane and a cobblestone-like cortical malformation similar to the phenotype seen in Gpr56 null mutant mice. Functional studies suggest that the interaction of collagen III with its receptor GPR56 inhibits neural migration in vitro. As for intracellular signaling, GPR56 couples to the Gα(12/13) family of G proteins and activates RhoA pathway upon ligand binding. Thus, collagen III regulates the proper lamination of the cerebral cortex by acting as the major ligand of GPR56 in the developing brain.