Worm Breeder's Gazette 14(4): 75 (October 1, 1996)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Biology, University of California, San Diego La Jolla, CA 92093-0116
Previously our lab observed that cha-1 mutants, which are defective in choline acetyltransferase, an enzyme required for the synthesis of acetylcholine (Ach), are both Egl-c and serotonin hypersensitive. This suggests that Ach plays an inhibitory role in egg-laying. This is a surprising result since the cholinergic agonist, levamisole, stimulates egg-laying. Further evidence of acetylcholine's regulatory role is that the ace-2; ace-1 double mutant is egg-laying defective (Egl-d). The ace-2; ace-1 double mutant, is defective in two of three Acetylcholine esterases and thus has very low levels of Ach esterase activity. Additionally we have obtained pharmacological evidence for this proposed down-regulatory mechanism. Application of mecamylamine, a general cholinergic antagonist, stimulates egg-laying. Interestingly, carbachol, a general cholinergic agonist also stimulates egg-laying but requires the HSN's while mecamylamine can also stimulate egg-laying in egl-1 mutants. This leads us to the belief that Ach could have a stimulatory role that requires the HSN's and also have an inhibitory role that is parallel to the HSN's. We have tested mutants known to affect Ach receptor function for serotonin hypersensitivity ( unc-29, unc-38, unc-63, unc-74, lev-1, lev-9, and lev-10). All of the mutants conferred hypersensitivity to serotonin except lev-1 and lev-9 gene mutations. These results suggest that Ach is working through nicotinic cholinergic receptors, though we haven't excluded the possibility that Ach may also be working via muscarinic cholinergic receptors. Furthermore, we have attempted to identify the location of Ach release (i.e. from the VA's, VB's, or VC's). Using an unc-17 (e813) allele, shown by Jim Rand to be a promoter mutation which blocks Ach synthesis in the VA's and VB's but not in the VC's, we have found that these mutants are Egl-c and serotonin hypersensitivity. This result is interesting since the VC's, rather than the VA's and VB's, seemed to be more likely to function as regulators of the vulval muscle because of their location and synaptic connections. We are now taking further steps to attempt to identify the location of the cholinergic receptors (i.e. on nervous vs. muscle tissue or both). We are beginning mosaic analysis to answer this question. In addition we are carrying out a screen to identify genes that rescue the Egl phenotype of the ace-2; ace-1 double mutant.