To identify Galpha proteins that play key roles in fat metabolism, we performed a screen for viable Galpha loss-of-function mutants that exhibited altered intestinal fat compared to wild type, measured using Oil Red O. One of the Galpha mutants that expressed a dramatic reduction in intestinal fat is
gpa-3.
gpa-3 is a Gs-like Galpha protein and is expressed exclusively in the nervous system, suggesting that it is part of a neuroendocrine pathway that connects nervous system function with intestinal fat metabolism. In this study, we are undertaking a systematic approach to trace the molecular and cellular details of this pathway.We have taken two complementary approaches to define the role of
gpa-3. Because
gpa-3 is expressed in 8 pairs of amphid sensory neurons, we designed a transgenic rescue strategy to restore
gpa-3 expression to subsets of these neurons in
gpa-3 mutants. Our neuron-specific rescue approach has identified 2 pairs of neurons which are sufficient for the
gpa-3-mediated regulation of fat metabolism. Preliminary studies indicate that enhanced fat loss, rather than diminished fat production, underlies the reduced body fat of
gpa-3 mutants. Next, we are conducting genetic epistasis analyses to identify downstream regulators of
gpa-3. Our studies thus far indicate a role of cAMP as the downstream effector of
gpa-3 signaling. Furthermore,
gpa-3;
unc-31 double mutants were created to determine if neuropeptide secretion is the method of
gpa-3 mediated signal propagation. Interestingly, our results show that this action is independent of
unc-31.
unc-31 mutants express a high-fat phenotype, however, the low-fat phenotype of
gpa-3 loss is not suppressed in
gpa-3;
unc-31 double mutants, suggesting an
unc-31- and neuropeptide-independent mode of regulation downstream of
gpa-3.Our continued studies focus on determining the mechanism of action, in particular the method of synaptic release used to relay the neuroendocrine signal from our identified amphid sensory neurons to the intestine.