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.

Putative Serotonin-deficient Mutants of C. elegans

B. Horvitz, J. Sulston

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.