Figure 1.

Reducing REC-8 function rescues the embryonic lethality of spo-11 mutants. (A) The self progeny of spo-11(me44) mutant hermaphrodites exhibit much higher levels of embryonic lethality than the self progeny of rec-8(ok978) animals. (B) Mating crosses demonstrate that most of the lethality of rec-8 embryos results from sperm abnormalities (likely aneuploidy), while spo-11 embryos die from defects in oogenesis and spermatogenesis. Data shown hereafter represent analyses of oocyte meiosis (mutant mothers mated with wild-type males). Analyses of the self progeny of mutant hermaphrodites are included in Supplemental Figure S4. (C) Reducing REC-8 function suppresses the embryonic lethality of spo-11 mutants. (D) DAPI staining and S10-phosphorylated histone H3 or AIR-2 staining of meiotic chromosomes in prometaphase I. The six homolog pairs of wild-type animals are held together by SCC and the CO. AIR-2 localizes at the midbivalent in wild-type worms, where it phosphorylates histone H3 on Ser 10. PhosH3(S10) is present between the discrete sister chromatids of rec-8(ok978) worms. In contrast, discrete sisters are rarely observed following NEBD in spo-11(me44) worms, and a patch of phosH3(S10) is present on a subset of univalents. Discrete sisters can be resolved in spo-11 rec-8 animals; however, AIR-2 is only present between sisters in some univalents. (E) Synergistic embryonic lethality occurs in rec-8(ok978); coh-4(tm1857) coh-3(gk112) mutants. (F) Disrupting NHEJ with a deletion allele of lig-4 does not substantially increase the lethality of rec-8 mutants, suggesting that DSBs made in rec-8 mutants are repaired by a different mechanism, likely homologous recombination. (G) SCC persists until anaphase II in spo-11 mutants. After anaphase I and extrusion of the first polar body (arrows), sister chromatids remain together in wild-type and spo-11 zygotes (arrowheads), while only detached sisters are visible in rec-8 mutants.