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GPR4 is a G protein-coupled receptor expressed in the vasculature, lung, kidney, and other tissues. In vitro ectopic overexpression studies implicated GPR4 in sensing extracellular pH changes leading to cyclic AMP (cAMP) production. To investigate its biological roles in vivo, we generated GPR4-deficient mice by homologous recombination. Whereas GPR4-null adult mice appeared phenotypically normal, neonates showed a higher frequency of perinatal mortality. The average litter size from GPR4-/- intercrosses was ∼30% smaller than that from GPR4+/+ intercrosses on N3 and N5 C57BL/6 genetic backgrounds. A fraction of knockout embryos and neonates had spontaneous hemorrhages, dilated and tortuous subcutaneous blood vessels, and defective vascular smooth muscle cell coverage. Mesangial cells in kidney glomeruli were also significantly reduced in GPR4-null neonates. Some neonates exhibited respiratory distress with airway lining cell metaplasia. To examine whether GPR4 is functionally involved in vascular pH sensing, an ex vivo aortic ring assay was used under defined pH conditions. Compared to wild-type aortas, microvessel outgrowth from GPR4-null aortas was less inhibited by acidic extracellular pH. Treatment with an analog of cAMP, a downstream effector of GPR4, abolished microvessel outgrowth bypassing the GPR4-knockout phenotype. These results suggest that GPR4 deficiency leads to partially penetrant vascular abnormalities during development and that this receptor functions in blood vessel pH sensing. [ABSTRACT FROM AUTHOR]

-cell death-associated gene 8 (TDAG8) is a G-protein-coupled receptor transcriptionally upregulated by glucocorticoids (GCs) and implicated by overexpression studies in psychosine-mediated inhibition of cytokinesis and in GC-induced apoptosis. To examine the physiological function of TDAG8, we generated knockout (KO) mice by homologous recombination. An enhanced green fluorescent protein reporter was knocked into the disrupted tdag8 locus to allow the analysis of TDAG8 expression in living cells. Interestingly, we found that during thymocyte development, TDAG8 expression resembled the dynamic regulation described for known modulators of GC-induced apoptosis, including Bcl-2, Notch1, and GC receptor. TDAG8 was expressed in double-negative cells, was downregulated at the double-positive transition, and was upregulated in single-positive thymocytes. However, despite this striking expression pattern, maturation and selection of thymocytes, as well as major immune functions, were not affected in TDAG8 KO mice. In contrast to previous overexpression results, TDAG8 was dispensable for psychosine-induced formation of multinucleated cells. Furthermore, TDAG8 KO thymocytes showed normal apoptosis following in vivo and in vitro GC treatment. These results, while establishing a useful reporter strain to study T-lymphocyte maturation, argue against a critical role for TDAG8 in immune development, psychosine-mediated inhibition of cytokinesis, and GC-induced cell death. [ABSTRACT FROM AUTHOR]