Our laboratory studies G protein signaling in mouse development and adult behavior using transgenic and mouse embryonic stem cell technology, in conjunction with biochemical studies. G protein signaling constitutes a fundamental mechanism of intercellular communication used by all eukaryotes. The signaling pathways have several components, each encoded by distinct multigene families. G proteins couple extracellular signals received by receptors to the regulation of effector proteins that generate intracellular second messengers. The Regulators of G protein Signaling (RGS) are intracellular inhibitors of G protein signaling. Biochemical analysis demonstrated that RGS proteins are GTPase activating proteins (GAPs) for heterotrimeric G protein alpha subunits of the Gi and/or Gq class. Thus, the timing, duration, and intensity of G protein signaling is regulated by the combined actions of hormone-bound receptors and RGS proteins. Mammals utilize these elaborate mechanisms to initiate and terminate G protein signaling in sensory transduction systems, such as photoreceptor cells in the retina, and a variety of other specialized functions in terminally differentiated cells. G proteins are also expressed early in mammalian development and in pluripotent progenitor cells of adults. Our laboratory is studying RSG/Gq-mediated signaling in heart development, craniofacial development, and peripheral regulation of feeding behavior in adult mice.