Genetic and Cellular Basis for Acetylcholine Inhibition ofCaenorhabditis elegansEgg-Laying Behavior

Abstract

Egg-laying behavior in Caenorhabditis elegans is activated by signaling through the G-protein G(rho)q and inhibited by signaling through a second G-protein, G(rho)o. Activation of egg laying depends on the serotonergic hermaphrodite-specific neurons (HSNs), but the neurotransmitter(s) and cell(s) that signal to inhibit egg laying are not known. Mutants for G-protein signaling genes have well characterized defects in egg laying. Here we present an analysis of mutants for other genes reported to lack inhibition of egg laying. Of the nine strongest, six have morphological defects in the ventral-type C (VC) neurons, which synapse onto both the HSNs and the egg-laying muscles and are thus the third cell type comprising the egg-laying system. Laser-ablating VC neurons could also disrupt the inhibition of egg laying. The remaining three mutants (unc-4, cha-1, and unc-17) are defective for synthesis or packaging of acetylcholine in the VCs. The egg-laying defects of unc-4, cha-1, and unc-17 were rescued by VC-specific expression of the corresponding cDNAs. In addition, increasing synaptic acetylcholine by reducing acetylcholinesterase activity, with either mutations or the inhibitor aldicarb, decreased egg laying. Finally, we found that a knock-out for the HSN-expressed receptor G-protein-coupled acetylcholine receptor 2 (GAR-2) shows a partial defect in the inhibition of egg laying and fails to respond to aldicarb. Our results show that acetylcholine released from the VC neurons inhibits egg-laying behavior. This inhibition may be caused, in part, by acetylcholine signaling onto the HSN presynaptic terminals, via GAR-2, to inhibit neurotransmitter release.

Genetic Interactions Between UNC-17/VAChT and a Novel Transmembrane Protein in Caenorhabditis elegans

“…The suppression is dominant ( Figure 1A), and transgenic expression of SUP-1(G84E) restores locomotion and swimming behavior in unc-17(e245) mutant animals. We note that additional unc-17 mutant phenotypes have been reported, including reduced growth rate, small adult size, decreased pharyngeal pumping, reduced defecation rate, and constitutive egg laying Avery 1993;Nguyen et al 1995;Bany et al 2003), and these phenotypes are also suppressed by sup-1 mutations (not shown).…”

“…The suppression is dominant ( Figure 1A), and transgenic expression of SUP-1(G84E) restores locomotion and swimming behavior in unc-17(e245) mutant animals. We note that additional unc-17 mutant phenotypes have been reported, including reduced growth rate, small adult size, decreased pharyngeal pumping, reduced defecation rate, and constitutive egg laying Avery 1993;Nguyen et al 1995;Bany et al 2003), and these phenotypes are also suppressed by sup-1 mutations (not shown).The SUP-1 protein SUP-1 is a member of the DUF2650 subfamily of STMC6 (single-transmembrane proteins with conserved 6 cysteines) family of proteins; STMC6 proteins are single-transmembrane proteins that have a conserved pattern of cysteines in their N-terminal domains (Pei and Grishin 2012). In addition, many members of the family have cysteine residues predicted to be palmitoylated near the cytoplasmic face of the transmembrane segment.…”

Reduced expression of BTBD10, an Akt activator, leads to motor neuron death

“…Six hermaphrodite-specific VC neurons, which extend synapses onto egg-laying muscles and neurons, were labeled by the pes-10::GFP reporter, named vsIs13 (Figure 4c). 23 In all, 4% and 6% of young-adult vsIs13 and tm3335;vsIs13 worms lost at least one VC neuron, respectively (Figure 4c). However, at the age of 17 days, 51.7% of vsIs13 worms lost at least 1 VC neurons and 84% of tm3335;vsIs13 worms lost at least 1 VC neuron (Figure 4d).…”

SER-7, aCaenorhabditis elegans5-HT7-like Receptor, Is Essential for the 5-HT Stimulation of Pharyngeal Pumping and Egg Laying

“…Acetylcholine can either stimulate egg laying, as demonstrated by the addition of the nicotinic agonist levamisole or inhibit egg laying, by the activation of Ga i/o -coupled muscarinic receptors (GAR-2?) on the HSNs that inhibit neurotransmitter release (Weinshenker et al 1995;Bany et al 2003). Physiologically, the overall effects of acetylcholine appear to be inhibitory (Bany et al 2003).…”

“…5-HT switches the muscle from an inactive to an active state capable of contraction 1 (Waggoner et al 1998). In contrast, the HSNs, which synapse onto the vulval muscle, appear to express Ga i/ocoupled receptors that inhibit neurotransmitter release and egg laying (Bany et al 2003;Shyn et al 2003).…”