Gq/EGL-30 stimulates neurotransmission, in part by activating phospholipase C/EGL-8 and UNC-13. However, there is evidence that other pathways operate downstream of EGL-30 to regulate neurotransmission. To identify genes in such pathways, we screened for suppressors of the activated Gq mutant
egl-30(
tg26). We expected to find mutants in the canonical pathway (
egl-30,
egl-8,
unc-13) as well as in other parallel pathways. We screened approximately 18,000 ENU-mutagenized genomes and isolated 43 mutants that suppress the hyperactive, small size and slow growth phenotypes of
egl-30(
tg26). These include mutations in at least sixteen genes not known previously to function in Gq signaling at the synapse. When crossed out of the
egl-30(
tg26) background, many of these mutants exhibit an unmotivated movement phenotype; they are capable of coordinated movement when prodded or in the absence of food, but show little spontaneous movement on food. Thus, these genes appear to function in the regulation of movement rather than the execution of coordinated movements. One of the new genes encodes a novel conserved protein with a small GTPase effector domain (the RUN domain). Because the small GTPase Rho has been implicated as a downstream effector of Gq, we wondered if the RUN protein might be a Rho effector. However, genetic interactions suggest that RUN acts in parallel to Rho. We looked at other small GTPase mutants and found that mutants in
unc-108/rab-2 have an unmotivated phenotype very similar to RUN mutants. Furthermore,
rab-2 mutants suppress
egl-30(
tg26), and double mutants of RUN with
rab-2 do not appear to have a stronger phenotype than the single mutants. Thus, genetic data suggest that RAB-2 and RUN may act in the same pathway. We are in the process of examining whether these proteins physically interact. RUN is expressed widely in the nervous system and in other tissues. In neurons, RUN appears to be concentrated in punctate positions in the cell body that may represent some secretory compartment. Tissue-specific rescue experiments indicate that RUN acts in neurons to control movement, but cholinergic expression is not sufficient. We have also cloned two other unmotivated mutants. Genetic interactions suggest that these genes may act in the same pathway as RUN. The RUN pathway may define a third Gq signaling pathway, acting in parallel to phospholipase C and Rho.