Several distinct processes occur during meiosis I to ensure that homologous chromosomes accurately segregate away from each other. These include homologous pairing, synapsis, recombination and checkpoint regulation of meiotic progression. However, the mechanisms underlying accurate chromosome segregation during meiosis I are poorly understood at the molecular level. We have investigated the roles of ZTF-8, a novel and highly conserved protein identified through an RNAi screen for meiotic candidates. We have found that ZTF-8 plays a role in DSB repair in the germline, in coordination with the DNA damage response 9-1-1 complex. ZTF-8 is observed localizing in nuclei at the pre-meiotic tip (mitotic nuclei) in the germline. ZTF-8 signal then decreases upon entrance into meiosis followed by an increase in pachytene, which persists throughout late prophase. Interestingly, we identified UBC-9 and SMO-1 as binding partners for ZTF-8 in a yeast two-hybrid screen. Moreover,
ubc-9 mutants exhibit an altered localization of ZTF-8. Taken together, these data suggest a tight regulation of ZTF-8 at the protein level, potentially via ubiquitination, between exit from mitosis and entrance into pachytene. Several observations implicate ZTF-8 as playing an important role in DNA repair. First,
ztf-8 mutants exhibit activation of a DNA damage checkpoint as supported by the presence of enlarged mitotic nuclei and elevated levels of ATL-1, a DNA damage checkpoint protein, in these germline nuclei. Second, levels of RAD-51 foci are elevated both in mitotic as well as in meiotic pachytene nuclei in
ztf-8 mutant germlines compared to wild type, suggesting either increased DSB formation or an impaired ability to repair DSBs. In addition,
ztf-8 mutants exhibited increased levels of germ cell apoptosis, further suggesting a defect in DNA repair and activation of a DNA damage checkpoint. Exquisite specificity in DNA damage sensitivity is observed in
ztf-8 mutants. Specifically, embryonic lethality (decreased hatching %) is induced following exogenous DSB formation by g-IR, but not following exposure to UV, nitrogen mustard and camptothecin. Moreover, replication arrest is observed following hydroxyurea (HU) treatment. In addition, both g-IR and HU treatments altered the localization pattern of ZTF-8 in the germline. Finally,
clk-2 mutants are synthetic lethal with
ztf-8, suggesting a link to the DNA damage checkpoint. This is further supported by epistasis analysis which places
ztf-8 acting downstream of
hus-1, a member of the 9-1-1 complex. Taken together, our studies identify ZTF-8 as a novel protein required for the maintenance of genomic integrity in the germline and reveal a link with the DNA damage response pathway.