Worm Breeder's Gazette 10(2): 61

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.

Identification of a Paternal Effect Embryonic Lethal Mutant

David Hill, Diane Shakes, Steven L'Hernault, Samuel Ward, Susan Strome

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.