Mutations in
goa-1, which encodes the a subunit of the Go trimeric G-protein, result in hyperactive locomotion, foraging, and egg laying. To identify further components of this G-protein signaling pathway we have screened for further mutants with similar phenotypes to those of
goa-1. In this manner we have isolated 18 further genes. We have cloned 2 of these genes. The first,
dgk-1, encodes a diacylglycerol kinase and DGK-1 expressed in HEK 293 cells is able to phosphorylate diacylglycerol to produce phosphatidic acid in an in vitro assay. A rescuing
dgk-1::gfp transgene is expressed throughout the nervous system and a rescuing hs::
dgk-1 transgene indicates that
dgk-1 is required in the adult nervous system. We have also cloned the
cat-1 gene, which was originally identified due to reduced levels of dopamine and serotonin (Sulston et al. 1975, Loer and Kenyon 1993). The
cat-1 gene encodes a monoamine vesicular transporter required for the transport of either serotonin or dopamine from the cytoplasm into vesicles prior to their release from neurons (Nurrish et al. 1997 IWM, Duerr et al. 1997 IWM). A rescuing
cat-1::gfp transgene is expressed in all the serotonergic and dopaminergic cells. The identification of
cat-1 suggests that our screen has identified genes required for either serotonin or dopamine signaling or both. Addition of exogenous serotonin or dopamine causes a reduction in locomotion and indeed both
goa-1 and
dgk-1 are defective in their response to serotonin while retaining a robust response to dopamine. Thus both
goa-1 and
dgk-1 are required in cells responding to serotonin. Furthermore,
dgk-1 mutations block the lethargic locomotion effects of over-expressing either wild type or a gain of function GTPase defective GOA-1 protein, suggesting that
dgk-1 acts downstream of or in parallel with
goa-1. The simplest model for these data is that serotonin, when used to modulate locomotion, binds to a seven transmembrane serotonin receptor coupled to
goa-1. Activated
goa-1 then signals downstream via a pathway which requires the presence of functional
dgk-1. One possibility is that
dgk-1 is a direct downstream target of
goa-1. We are using a variety of approaches to test this model such as testing for changes in
dgk-1 activity in response to G-proteins, identification of the receptors involved in serotonin modulation of locomotion, and cloning of the remaining 16 genes identified in our screen. Sulston, J., Drew, M., and Brenner, S. (1975) J.Comp.Neurol. 163, 215-226. Loer, C.M. and Kenyon, C.J. (1993) J. Neurosci. 13, 5407-5417