The frequency of egg-laying behavior by C. elegans is regulated by environmental conditions: in the presence of abundant food eggs are laid about every 30 minutes, but in the absence of food egg laying rarely occurs. To understand how the activities of the egg-laying neurons and/or muscles are modulated to achieve this regulation, we are studying mutations that disrupt the regulation of egg laying. Two of the genes identified by these mutations have been cloned:
egl-10 positively regulates egg laying and encodes a homolog of
sst2, a gene that controls G protein signaling in yeast (1);
goa-1 negatively regulates egg laying and encodes a G protein alpha subunit homolog (2,3). These results suggest that the control of egg laying involves a G protein signaling pathway that may mediate the action of neurotransmitters on the egg-laying neurons and/or muscles to modulate the activities of these cells.
egl-10 is of particular interest, since it is a member of a newly discovered family of homologous genes that we have named RGS genes (RGS, regulator of G protein signaling). This family includes
egl-10,
sst2, at least three additional C. elegans genes, and at least 15 mammalian genes that we identified by their similarity to
egl-10. Genetic studies in worms and yeast suggest that the EGL-10 and Sst2p proteins have similar functions: each appears to act upstream of a G protein to inhibit signaling. We hypothesize that the other members of the family of RGS proteins might function to regulate many different G protein signaling pathways. We would like to understand the biochemical mechanism of action of the RGS proteins. One class of molecular models consistent with the genetic studies in worms and yeast involves a direct interaction between RGS proteins and G proteins. This class of models is supported by the recent identification of an interaction between an RGS protein and a G protein alpha subunit in a yeast two-hybrid system (4). RGS proteins could bind to G proteins to uncouple them from receptors, to uncouple them from their downstream effectors, to affect interactions between the various G protein subunits, or to activate the GTPase activity of G protein alpha subunits. To distinguish among these models, we have begun to express and purify recombinant forms of EGL-10 and GOA-1 and are investigating the properties and interactions of these proteins in vitro. Both proteins have been expressed in the baculovirus system, and progress in analysis of these proteins will be presented. 1. Koelle, M.R., and Horvitz, H.R (1996). Cell 84, 115-125. 2. Segalat, L., Elkes, D.A., and Kaplan, J.M. (1995). Science 267, 1648-1651. 3. Mendel, J.E., Korswagen, H.C., Liu, K.S., Hajdu-Cronin, Y.M., Simon, M.I., Plasterk, R.H, and Sternberg, P.W. (1995). Science 267, 1652-1655. 4. De Vries, L., Mousli, M., Wurmser, A., and Farquhar, M.G. (1995). Proc. Natl. Acad. Sci. USA 92, 11916-11920.