The NCA-1 and NCA-2 Ion Channels Function Downstream of Gq and Rho To Regulate Locomotion in Caenorhabditis elegans

Abstract

The heterotrimeric G protein G positively regulates neuronal activity and synaptic transmission. Previously, the Rho guanine nucleotide exchange factor Trio was identified as a direct effector of G that acts in parallel to the canonical G effector phospholipase C. Here, we examine how Trio and Rho act to stimulate neuronal activity downstream of G in the nematode Through two forward genetic screens, we identify the cation channels NCA-1 and NCA-2, orthologs of mammalian NALCN, as downstream targets of the G-Rho pathway. By performing genetic epistasis analysis using dominant activating mutations and recessive loss-of-function mutations in the members of this pathway, we show that NCA-1 and NCA-2 act downstream of G in a linear pathway. Through cell-specific rescue experiments, we show that function of these channels in head acetylcholine neurons is sufficient for normal locomotion in Our results suggest that NCA-1 and NCA-2 are physiologically relevant targets of neuronal G-Rho signaling in .

Dopamine negatively modulates the NCA ion channels in C. elegans

“…Recently, we identified the cation channels NCA-1 and NCA-2 as downstream targets of this G q -Rho pathway. Specifically, we found that mutations in genes that encode accessory subunits of the NCA channels (u nc-79 , unc-80 ) or in the NCA channels per se ( nca-1; nca-2 ) suppress the neuronal phenotypes of activated G q and activated Rho [12]. Moreover, mutations in the Rho-NCA pathway suppress the loopy posture of the activated G q mutant more strongly than do mutations in the canonical PLCβ pathway [12].…”

“…Specifically, we found that mutations in genes that encode accessory subunits of the NCA channels (u nc-79 , unc-80 ) or in the NCA channels per se ( nca-1; nca-2 ) suppress the neuronal phenotypes of activated G q and activated Rho [12]. Moreover, mutations in the Rho-NCA pathway suppress the loopy posture of the activated G q mutant more strongly than do mutations in the canonical PLCβ pathway [12]. Like mutations in the Rho-NCA pathway, grk-2 mutants also strongly suppress the loopy posture of an activated G q mutant (Figs 1A, 4D and 4E), suggesting that grk-2 may affect signaling through the Rho-NCA pathway.…”

“…We also built double mutants of grk-2 and a dominant activating mutation in the NCA-1 channel gene, nca-1(ox352) , referred to here as Nca* [12,24]. Like Rho*, Nca* mutants have a loopy posture and slow locomotion.…”

“…Given that grk-2 partially suppresses Rho*, we hypothesized that GRK-2 is not absolutely required for Rho-NCA signaling, but provides modulatory input. To test this hypothesis, we built double mutants between grk-2 and nlf-1 , which is partially required for localization of the NCA-1 and NCA-2 channels and has a weak fainter mutant phenotype [12,91]. A grk-2 mutation strongly enhanced the weak fainter phenotype of an nlf-1 mutant so that the double mutants resembled the stronger fainter mutants that completely abolish NCA-1 and NCA-2 channel activity (Fig 6A and 6B).…”

“…We recently identified the C . elegans orthologs of the NALCN ion channel, NCA-1 and NCA-2, as downstream targets of a G q -Rho signaling pathway [12]. We aim to understand the mechanism of activation of this pathway.…”