Worm Breeder's Gazette 8(3): 47
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 isolated 45 C. elegans egg-laying defective mutants that appear to have functionally impaired HSNs (see Newsletter Vol. 8 No. 1). (The HSNs are two motorneurons that innervate the vulval muscles.) These mutants define at least 14 genes, of which we have now mapped 11 (see Map on the next page). In the last Newsletter (Vol. 8 No. 2) we reported that in the wild type the HSNs are stained by anti- serotonin antisera, and we described the phenotypes of some of these HSN-defective mutants as observed after staining with anti-serotonin antisera. We have now examined the appearance of the HSNs in mutants representing all 14 of these genes using indirect immunofluorescence to visualize serotonin and Nomarski optics to visualize cell bodies ( see Table on the next page; an * in the table indicates a mutant allele studied by microscopy). These HSN-defective mutants can be divided into five categories. Mutants in Category A lack HSNs by both criteria; mutations in three of the five genes of this category appear to cause HSNs to undergo programmed cell death, as these mutations are suppressed by mutations in the genes ced-3 or ced-4 (which block the onset of programmed cell deaths; see Ellis et al., this Newsletter). Mutants in Category B appear to generate abnormal HSNs, which can be absent or variably mispositioned and which when present invariably lack serotonin. The mutant egl-46(n1127), which defines Category C, has HSN cell bodies in almost normal positions but lacks serotonin in the HSNs. (This mutant contains serotonin in the other normally serotonin-positive neurons that are visualized after staining with the anti-serotonin anti-sera.) It has not been unambiguously demonstrated that the cells considered to be misplaced HSNs in Categories B and C mutants are indeed HSNs. The mutant egl-43(n997), which defines Category D, appears to be defective in the migration of the HSNs. (HSN migration is a normal aspect of embryonic development.) As seen with Nomarski optics, egl-43 animals lack HSNs in their normal positions; serotonin-staining reveals ectopic serotonin-positive cells variably located along the path of HSN migration (from the postanal region to near the position of the vulva). A double mutant containing egl-43(n997) and the Category A mutation egl-41(n1069) lacks these ectopic serotonin- positive cells, indicating that they are mispositioned HSNs. The misplaced putative HSNs of egl-43 animals have aberrant processes: some run abnormally long distances along the ventral cord into the nerve ring (normal HSNs run from the region of the vulva along the ventral cord into the nerve ring), others are bipolar, and others send a process posteriorly to the tip of the tail or anteriorly via a sublateral route. The putative HSNs of egl-43 animals seem to migrate slightly farther on average at 20 C or 25 C an they do at 15 C. Category E mutants have HSNs that appear normal as visualized with both Nomarski and fluorescence microscopy. [See figure 1]