Worm Breeder's Gazette 2(2): 37
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.
Exogenous serotonin (5-hydroxytryptamine) stimulates about 20-fold the rate of egg-laying by adult C. elegans hermaphrodites. Mutants defective in egg-laying can be divided into two classes according to their responses to serotonin: those blocked prior to the point at which serotonin acts to induce egg-laying lay eggs in the presence of exogenous serotonin, whereas those blocked at or after that point do not lay eggs. Forty-one egg-laying deficient mutants were exposed to serotonin. Two of these mutants -- E1416 (unc-86 III) and E1430 (unc- 91 I) -- were induced to lay eggs by serotonin. A substance similar to serotonin in its yellow formaldehyde-induced fluorescence (FIF) has been identified in the neurosecretory motor neurons (NSM's) of the pharynx; these neurons also accumulate exogenously supplied serotonin. Thus, the pharyngeal NSM's are likely to be serotoninergic. Of 41 egg-laying deficient mutants examined, two were serotonin-deficient (i.e. had reduced levels of yellow FIF in the NSM's): E1416 and E1430. E1416 displayed no detectable serotonin, even in the double mutant E1416-E1111 (unc-86 III; cat-1 X) (cat-1 X, which reduces the FIF in both dopaminergic and serotoninergic processes, also increases the level of serotonin in the NSM cell bodies). E1430 showed reduced but detectable levels of serotonin. The egg-laying defect of E1416 is more extreme than that of E1430. In each of these mutant strains, the egg-laying and serotonin defects are very closely linked, indicating that a single genetic alteration is probably responsible for both phenotypes. Both E1416 and E1430 take up exogenous serotonin into the NSM's. From these observations, we suggest that the serotoninergic NSM's induce egg-laying in wild-type C. elegans and that the mutants E1416 and E1430 are defective in egg-laying because of their reduced levels of serotonin. However, as both E1416 and E1430 display complex phenotypes, this proposal must be regarded as tentative.