Worm Breeder's Gazette 10(2): 61
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The mutant spe-11 was isolated in a screen for spermatogenesis- defective mutations (see L'Hernault, Shakes, & Ward, WBG 90, p. 98). Recent genetic and phenotypic analyses have demonstrated that spe-11 sperm do, in fact, fertilize oocytes, but that the resulting zygotes develop abnormally. The allele hc90 is non-conditional and non-leaky. Homozygous hc90 hermaphrodites lay abnormal self-cross embryos. Two lines of evidence demonstrate that the defects in embryogenesis result from abnormal sperm: 1) hc90 hermaphrodites mated to wild type males produce viable embryos; 2) dpy-5/dpy-5 hermaphrodites mated to hc90/ hc90 males fail to produce non-Dpy progeny and produce many dead 'hc90-like' embryos. Mating of hc90/hc90 hermaphrodites to heterozygous hc-90+ males results in the production of viable embryos of both of the expected genotypes (hc90/+ and hc90/hc90); this result suggests that wild-type hc90 product is synthesized during spermatogenesis and that wild-type product enables sperm carrying a mutant allele to initiate or participate in normal embryogenesis. The lack of a dominant effect also suggests that the hc90 mutant product is not a poison. Therefore the wild-type hc90 gene may encode a product that sperm must provide for correct zygote development. Embryos that result from fertilization by hc90 sperm show very early abnormalities: 1) The evidence that hc90 sperm penetrate oocytes is the presence of two pronuclei at opposite ends of early embryos and positive staining of embryos with antibodies to sperm-specific antigens. 2) There are no observable polar bodies, so the anterior- posterior axis is not obvious. We have not yet determined whether the newly fertilized eggs complete meiosis. 3) Embryos have weak eggshells, and are osmotically sensitive and rounder than normal. 4) Pseudocleavage is aberrant and consists of the formation and retraction of a number of undirected pseudopodial blebs, in contrast to the localized membrane contractions seen in wild-type embryos. 5) Pronuclear migration occurs apparently normally and the pronuclei meet at one end of the round zygote. 6) The orientation of the first mitotic spindle appears to be random. The spindle looks relatively normal when stained with anti-tubulin antibodies, although the microtubule density does not appear as high as in wild-type embryos. Antibody staining of the centrosomes located at the spindle poles appears normal. 7) Cleavage is variable, ranging from apparently normal cytokinesis to the complete absence of a cleavage furrow. 8) P granules coalesce during the first cell cycle, but they are not cortical, do not appear to be localized, and are not partitioned to specific blastomeres during cell divisions. 9) Embryos that remain unicellular undergo rounds of fairly synchronous mitosis and become multinuclear. Other embryos divide but often become multinuclear as well. 10) Late stage embryos do not express gut granules. The other allele of spe-11, hc77, is temperature-sensitive and shows variable expressivity. The embryos produced by hc77/hc77 hermaphrodites range from displaying as severe a phenotype as hc90/hc90 embryos to developing apparently normally into adults that themselves produce embryos with the same range of phenotypes. The finding that hc77/hc77 hermaphrodites raised at restrictive temperature during spermatogenesis and then shifted down to permissive temperature produce many healthy embryos suggests that hc77 is not temperature-sensitive for synthesis, but rather that the hc77 product is reversibly inactivated at high temperature.