The original mutation in
emb-27 (
g48ts)was reported to cause a striking very early maternal effect lethality in which self progeny from homozygous hermaphrodites arrest at the one cell stage (Isenenghi et al, (1983) and Denich et al, (1984)). In 1985, Fiebich and Cassada reported that
emb-27 also has a paternal effect in which defective embryos arrest development at the 100 cell stage. In our own studies of arrested embryo phenotypes, we have found them to be much more variable than previously reported. While some
emb-27 self progeny do arrest as polyploid unicellular embryos, others become multicellular. Using DAPI and an anti-tubulin antibody, we found that unicellular embryos frequently had multi-polar spindles. Lysis of embryos when not in embryonic buffer may explain the earlier reports of a uniform unicellular arrest. Our hemizygous deletion analysis of
g48ts in trans to deficiency strains in the LGII subcluster uncovered a previously unknown requirement for
emb-27 in gametogenesis of both hemaphrodites and males. Interestingly, we obtained different phenotypes with every deletion we examined. Under Normarski optics, some hemizygotes (
g48ts /mnDf93or mnDf106 )were severely defective in postproliferation germ cell development whereas others (
g48ts /mnDf91)resembled the
g48ts homozygotes by making fairly normal looking oocytes and sperm. This data demonstrates that
g48ts is not a null and suggests that the deletion breakpoints may define various regulatory regions of the gene. Further cytological analysis of DAPI stained hemizygous gonads showed that they contain germ cells with a range of chromosomal abnormalities. The healthier
g48ts /mnDf84animals exhibit slightly premature chromosomal condensation in the distal arm of the gonad whereas the more severely affected animals (
g48ts /mnDf93,mnDf106)exhibit noticeable missegregation of chromosomal material. The pseudoallelic series observed with the various hemizygotes predicts a potential ordering of the deletion breakpoints with the "right-edge" deletion breakpoints falling from left to right as shown below. Of course, molecular data will be needed to confirm this prediction. Data on
mig-5 bolsters our observations since
mig-5 complements mnDf91 and mnDf109 but not the others (Hedgecock lab, personal communication).
fer-15 fails to complement all of the deficiency strains with no obvious phenotypic differences between the different hemizygotes (L'Hernault, personal communication ). Work is currently underway to determine if oocyte and sperm-specific gene products are produced in the hemizygous animals. In addition, transmission electron microscopy will be used for a more detailed analysis of the observed gonadal abnormalities.l