Prior to fertilization, the C. elegans oocyte responds to an external, sperm-derived signal provided by major sperm protein (MSP). This signal releases the oocyte from its G2 arrest, initiating the meiosis I division (MI). In the absence of sperm entry, MSP-stimulated oocytes abort anaphase I, skip meiosis II (MII) and enter mitosis, suggesting a second signal provided upon sperm entry is required for the MII program. We discovered three similar paralogs,
memi-1, 2, and 3 (meiosis-to-mitosis transition), which encode oocyte components, that are required for completion of MI and entry into MII. Loss of all three paralogs results in a skipped-MII phenotype, however, a gain-of-function mutation,
memi-1(
sb41ts), results in fertilized embryos that complete MI, enter MII, but do not exit MII properly. Through whole genome RNAi screening, we previously identified a sperm-specific PP1 phosphatase,
gsp-3/4, as a suppressor of
memi-1(
sb41). A subsequent EMS-based suppressor screen recovered alleles of
gsp-4 and additional genes in this pathway. One of these, R03D7.5, encodes a putative GSK3 protein kinase. R03D7.5 mutants exhibit paternal-effect suppression of
memi-1(
sb41), suggesting that this GSK3 has some role in the sperm. R03D7.5 deletion homozygotes appear wild type, however, double-deletion analysis revealed functional redundancy with one other GSK3 member. The double-deletion hermaphrodites exhibit 45% embryonic lethality, which is completely rescued by mating to wild-type males. Approximately 35% of GSK-3 double-deletion fertilized embryos exhibited defects in MII, including cell-cycle delays and failed polar body extrusion. Together, this suggested that these genes encode sperm-specific components that have roles in the early embryo. Western blotting of FLAG- and Ollas-tagged worms revealed that both GSK3 homologs are detected in sperm-only
fem-3(
q20gf) worms but not in oocyte-only
fem-1(
hc17lf) females. Immunostaining for both proteins revealed a strong signal in sperm, which resembled the intracellular localization observed with anti-GSP-3/4 antibodies. Interestingly, R03D7.5
gsp-4 double mutants exhibit synthetic embryonic lethality (28%), and a triple-deletion (both
gsk3 genes and
gsp-4) produce 70% dead embryos, some of which skip female MII, similar to
memi-1/2/3(RNAi). Further characterization of the double GSK3 mutants revealed sister chromatid non-disjunction in 20% of male MII. GSK3 double-deletion sperm also exhibited reduced sperm motility in vivo and altered sperm morphology and slow pseudopod formation in vitro. Pseudopod treadmilling rates were also reduced in GSK3 double-deletion sperm. This work suggests that these GSK3s play a pivotal role during spermatogenesis and sperm motility, similar to GSP-3/4, and that these factors also participate in the MEMI pathway to regulate female MII.