Bride of sevenless, member of the class C family of seven-transmembrane G protein-coupled receptors
Bride of Sevenless (Boss) is a putative Drosophila melanogaster G protein-coupled receptor that functions as a glucose-responding receptor to regulate energy metabolism. Boss is expressed predominantly in the fly's fat body, a nutrient-sensing tissue functionally analogous to the mammalian liver and adipose tissues, and in photoreceptor cells. Boss, which is expressed on the surface of R8 photoreceptor cell, binds and activates the Sevenless receptor tyrosine kinase on the neighboring R7 precursor cell. Activation of Sevenless results in phosphorylation of the Sevenless, triggering a signaling transduction cascade through Ras pathway that ultimately leads to the differentiation of the R7 precursor into a fully functional R7 photoreceptor, the last of eight photoreceptors to differentiate in each ommatidium of the developing Drosophila eye. In the absence of either of Sevenless or Boss, the R7 precursor fails to differentiate as a photoreceptor and instead develops into a non-neuronal cone cell. Moreover, Boss mutants in Drosophila showed elevated food intake, but reduced stored triglyceride levels, suggesting that Boss may play a role in regulating energy homeostasis in nutrient sensing tissues. Furthermore, GPRC5B, a mammalian Boss homolog, activates obesity-associated inflammatory signaling in adipocytes, and that the GPRC5B knockout mice showed resistance to high-fat diet-induced obesity and insulin resistance.