Worm Breeder's Gazette 12(3): 110 (June 15, 1992)
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.
In the C. elegans hermaphrodite the sex myoblasts (SMs) generate the muscles that are required for egg laying. The SMs arise in the posterior of the animal (near P9 .p)and migrate anteriorly to a position flanking the center of the gonad (over P6 .p).There appear to be at least two mechanisms controlling the migration of the SMs in hermaphrodites: a gonad-independent mechanism that causes the SMs to migrate anteriorly into the correct region of the animal and a gonad-dependent mechanism that guides the SMs to their positions flanking the precise center of the gonad (Thomas et al., Cell 62: 1041). Certain mutations in egl-15 and egl-17 appear to convert the gonad-dependent attraction into a gonad-dependent repulsion. That is, the SMs in egl-15 or egl-17 mutant hermaphrodites are posteriorly displaced if the gonad is present, but migrate anteriorly if the somatic gonad is eliminated by laser killing of Z1 and Z4 (Stem and Horvitz, Development 113: 797).
The most plausible explanation for how mutations that fit the standard genetic criteria for reduction or loss of function could create a repulsion is that they are accessing a repulsive mechanism that normally acts in the organism. Such a repulsive mechanism might be involved in the posterior migration of SMs in the male. However, this gonad-dependent repulsion of the SMs would have to be redundant in males because the SMs continue to migrate posteriorly in the absence of the somatic gonad (Stern and Horvitz, Development 113: 797). We have shown that the male gonad can repel hermaphrodite SMs by using tra-1 ( rh132 )to place a male gonad into an otherwise hermaphrodite soma (Herman and Hedgecock, Nature 348: 169). As shown below, hermaphrodite SMs are posteriorly displaced in tra-1 ( rh1 32) animals. However, if the somatic gonad is eliminated by laser killing of Z1 and Z4 ,the SMs migrate anteriorly (p<0.0001). Taken at face value, these results are consistent with a model whereby the gonad dependent repulsion of the SMs in egl-15 and egl-17 mutant hermaphrodites occurs via the same mechanism as in the tra-1 ( rh1 32) animals. Our results cannot distinguish whether mutations in egl-15 and egl-17 eliminate the predominant gonad-dependent attraction to reveal an underlying gonad-dependent repulsion in hermaphrodites, or whether they result in the ectopic expression of
the repulsive mechanism in hermaphrodites.
Stem and Horvitz, Development 113: 797
Herman and Hedgecock, Nature 348: 169