The heterotrimeric G protein G o is abundantly expressed in mammalian brain. In the nematode Caenorhabditis elegans , a homolog of the alpha subunit of mammalian G o is encoded by the
goa-1 gene, which is widely expressed in the nervous system. Loss-of-function mutations in
goa-1 cause various behavioral defects including hyperactive locomotion and constitutive egg-laying. Although previous studies have revealed that GOA-1(G o alpha) and EGL-30(G q alpha) act antagonistically in modulating the neurotransmitter release at neuromuscular junctions, molecular functions of these G proteins in other neurons remain mostly unexplored. To clarify the role of GOA-1 and EGL-30 in more complex behaviors, we focused on chemotaxis behavior, which is mediated by many types of neurons including amphid sensory neurons. We found that both the loss-of-function mutant,
goa-1(
n1134) , and the strain overexpressing
egl-30(+) , syIs36[
egl-30(+)] , showed increased chemotaxis to several odorants, and had a defect in adaptation to AWC-sensed odorants. To identify the neurons in which
goa-1 functions in olfactory adaptation, expression of
goa-1(+) was driven by various promoters in
goa-1 mutants. When
goa-1(+) was expressed in a few sensory neurons including AWC by using
gcy-10 or
odr-3 promoters, adaptation defects of
goa-1 mutants were partially rescued. Furthermore,
goa-1(+) expression in several interneurons also partially rescued, suggesting that
goa-1 participate in multiple neurons in adaptation. To investigate the role of GOA-1/EGL-30 signaling pathways further, we expressed gain-of-function mutant
goa-1(gf) or
egl-30(gf) in AWC sensory neurons. The transgenic animals in which
goa-1(gf) was overexpressed in AWC exhibited hyperadaptive responses. On the other hand, overexpression of
egl-30(gf) in AWC caused severe defect in adaptation, suggesting that in AWC neurons, GOA-1 and EGL-30 signaling pathways modulate olfactory responses in opposite directions. It is known that one of the FMRFamide-related neuropeptide genes,
flp-1 , acts upstream of GOA-1/EGL-30 pathways to control locomotive behavior. We found that
flp-1 mutants are also defective for olfactory adaptation similarly to that observed in
goa-1 mutants. We are currently investigating whether FLP-1 signals upstream of GOA-1 to regulate olfactory adaptation.