Worm Breeder's Gazette 7(1): 81
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.
b245III is a temperature-sensitive mutation that blocks spermatogenesis and allows oogenesis in both males and hermaphrodites, and so appears to control an early switch between the two pathways of gamete differentiation. Varied temperature pulses were used to determine the period at 25 C needed to initiate oogenesis in males. A pulse of 8 to 10 hours, beginning at any time after 20 hours of age, will switch all males of a synchronized population to oogenesis as adults. A six-hour pulse switches a fraction of the population and blocks spermatogenesis in the rest. A four-hour pulse will similarly block spermatogenesis without initiating oogenesis, so that these worms as adults make a few sperm and then stop differentiating gametes. A two-hour pulse does not block spermatogenesis. Males from the six and eight-hour pulses that have switched to oogenesis consistently have 20 to 40 undifferentiated germ cells sandwiched between the sperm made initially and the oocytes made later. Thus, there seems to be a level of gene product at which the initiation of spermatogenesis is permanently blocked, but the process of oogenesis is not initiated. In a number of males given short pulses, so that oocytes were produced after some sperm was made, probable embryos were observed in Feulgen preparations. Most males had single 'embryos'; sometimes two were seen. These 'embryos' are spherical, appear to be membrane- enclosed, and contain from about 30 to 200 nuclei. None showed morphogenesis. However, in one 'embryo' of approximately 100 nuclei, 8 adjacent gut nuclei and a dead nucleus were distinguishable. The most likely explanation is self-fertilization by the sperm present, as embryos are never observed in B245 25 C hermaphrodites, which have functional oocytes but no sperm. It appears, then, that male oocytes can function to support at least early development, and that hermaphrodite gonadal structures may not be necessary for fertilization. Double mutants were made of B245 with tra-1 (e1099)III and isx-1 ( hc17)IV to look at the interactions of this mutant, which appears to affect primarily gamete determination, with mutants that affect somatic and gonadal sex determination as well as gamete differentiation. The b245 tra-1 (e1099) double mutant produced XX males as expected for the tra-1 mutant, and these males, if shifted to high temperature, produced oocytes like the b245 males. This independent expression of the phenotypes of the two single mutants can be interpreted either that the two genes operate in independent pathways, or that tra-1 acts earlier in the same pathway, if the tra-1( +) allele controls the hermaphroditic mode of expression of the b245(+) gene. The isx-1 and b245 mutations have very similar phenotypes, the only major difference being that isx-1 mutant males have feminized gonads, although their somatic sexual differentiation is male. The double mutant b245; isx-1(hc17) shows a much more extreme phenotype than either of the single mutant strains. At 16 C, most hermaphrodites make no sperm, showing the mutant phenotype even though both single mutants are temperature-sensitive. Males at 16 C have intersex gonads, but make sperm. At 25 C, hermaphrodites, as would be expected, are totally spermless. The 25 C males show an extreme phenotype with a very small intersex or undifferentiated gonad, and have no differentiated germ cells. The male tail does not develop beyond the L4 stage. This interaction suggests that the b245 gene is needed for male somatic and gonad differentiation as well as spermatogenesis, and that it acts in a common pathway with isx-1.