G proteins, chemosensory perception, and the C. elegans genome project: An attractive story.

Heterotrimeric G proteins, consisting of alpha, beta, and gamma subunits, couple ligand-bound seven transmembrane domain receptors to the regulation of effector proteins and production of intracellular second messengers. G protein signaling mediates the perception of environmental cues in all higher eukaryotic organisms, including yeast, Dictyostelium, plants, and animals. The nematode Caenorhabditis elegans is the first animal to have complete descriptions of its cellular anatomy, cell lineage, neuronal wiring diagram, and genomic sequence. In a recent paper, Jansen et al. used sequence searches of the C. elegans genome database to identify all heterotrimeric G protein genes (20 Galpha, 2 Gbeta, 2 Ggamma). C. elegans encodes one ortholog of each of the four Galpha classes found in metazoans and 16 new Galpha genes. The orthologous genes are widely expressed, whereas 14 of the divergent Galpha genes are almost exclusively expressed in sensory neurons where they may regulate perception and chemotaxis.