During fertilization, sperm entry triggers completion of female meiosis I (MI) and entry into meiosis II (MII). Although the molecular mechanism of this process is still unclear, we identified three maternally-expressed paralogs,
memi-1, 2 and 3 (meiosis-to-mitosis) that are required for sensing sperm entry. Loss of all three paralogs results in a skipped MII phenotype, however, a gain-of-function mutation,
memi-1(
sb41ts) results in embryos that are unable to exit MII properly. Previously, we found that RNAi knockdown of a sperm-specific PP1 phosphatase, GSP-3/4, suppressed
memi-1(
sb41). Through EMS screening, we recovered alleles of
gsp-4 and identified additional genes in this pathway. One of the genes, R03D7.5, encodes a putative GSK3 protein kinase. R03D7.5 deletion homozygotes appear wild type, however, double-deletion analysis revealed functional redundancy with one other GSK3 member. The GSK double-deletion worms exhibited embryonic lethality and lower brood sizes. The embryonic lethality was completely rescued by mating hermaphrodites to wild-type males. Furthermore, double-deletion males produced a significant number of inviable embryos when mated to
fog-2 hermaphrodites. Together, this suggested that these genes might encode sperm-specific components that have roles in the early embryo. Approximately 38% of GSK double-deletion fertilized embryos exhibited normal MI, but MII spindle assembly was delayed and the second polar body failed to extrude. This result suggested that these GSKs have a role in the early embryo. We also tested the relationship between GSP-3/4 and R03D7.5 and discovered a synthetic genetic interaction whereby R03D7.5(?)
gsp-4(?) mutants produce 30% dead embryos. Interestingly, the triple-deletion (both gsks and
gsp-4) produce many dead embryos, some of which skip MII, similar to
memi-1/2/3(RNAi). Therefore, R03D7.5 and
gsp-4 could participate in the MEMI pathway to specify MII after fertilization. Because of the genetic interaction between R03D7.5 and
gsp-4 in the early embryo, and the fact that GSP-3/4 is required for normal sperm motility and sperm meiosis, we also tested whether the GSKs have sperm functions. We found that the GSK double-deletion mutants exhibited reduced sperm motility in vivo, as well as altered sperm morphology and slow pseudopod formation in vitro. Consistent with these defects, pseudopod treadmilling rates were also reduced in the double-deletion mutant. As was previously reported for
gsp-3/4, we found that GSK double-deletion mutants display frequent chromosome segregation defects during sperm meiosis. This work suggests that the GSKs and PP1 phosphatases perform some similar functions with respect to sperm motility and meiosis, and they participate in post-fertilization functions involving MEMI.