Worm Breeder's Gazette 9(1): 57
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.
We have previously described 45 mutations that disrupt the functioning of the HSN motorneurons, which drive egglaying. Of these mutations, seven that define the two genes egl-44 and egl-46 display low levels of serotonin in the HSNs as visualized by indirect immunoflourescent staining. The other serotonergic cells (the NSMs and six or seven additional neurons in the head and pharynx) appear to have normal levels of serotonin. While constructing and characterizing strains containing pairs of mutations affecting the HSNs, we noticed that the HSNs in egl-43: egl-46 animals have increased levels of anti-serotonin staining compared to the levels seen in egl-44 and egl-46 mutants alone. The HSNs in egl-43 mutants fail to migrate from their birthplaces in the tail to their wild-type positions just posterior to the midpoint of the gonad. This result led us to theorize that the lower antiserotonin staining in egl-44 and egl-46 HSNs may be dependent on synapse formation between the HSN processes and their targets, the vulval muscles. To further test this hypothesis, we constructed four more double mutant strains, designed to disrupt these synapses. These double mutant strains are: egl-44: egl-44; egl-46: egl-31. The egl-15 mutation results in the incomplete migrations of the sex myoblasts, the ancestors of the vulval muscle cells. The egl-31 mutation results in abnormalities in the M cell divisions that generate the sex myoblasts. The level of anti-serotonin staining in the HSNs of each of these four strains is enhanced, compared to that seen in egl-44 and egl-46 alone. All six of the double mutant strains described above either remove the targets from the HSNs or the HSNs from their targets. Thus, the low level of anti-serotonin staining found in the HSNs of egl-44 and egl-46 animals seems to depend on HSN-vulval muscle synapse formation. This reduced anti-serotonin staining could be due to synaptic leakage of serotonin, faulty reuptake, or some other defect.