Ablation of Ggnbp2 impairs meiotic DNA double-strand break repair during spermatogenesis in mice.

Gametogenetin (GGN) binding protein 2 (GGNBP2) is a zinc finger protein expressed abundantly in spermatocytes and spermatids. We previously discovered that Ggnbp2 resection caused metamorphotic defects during spermatid differentiation and resulted in an absence of mature spermatozoa in mice. However, whether GGNBP2 affects meiotic progression of spermatocytes remains to be established. In this study, flow cytometric analyses showed a decrease in haploid, while an increase in tetraploid spermatogenic cells in both 30- and 60-day-old Ggnbp2 knockout testes. In spread spermatocyte nuclei, Ggnbp2 loss increased DNA double-strand breaks (DSB), compromised DSB repair and reduced crossovers. Further investigations demonstrated that GGNBP2 co-immunoprecipitated with a testis-enriched protein GGN1. Immunofluorescent staining revealed that both GGNBP2 and GGN1 had the same subcellular localizations in spermatocyte, spermatid and spermatozoa. Ggnbp2 loss suppressed Ggn expression and nuclear accumulation. Furthermore, deletion of either Ggnbp2 or Ggn in GC-2spd cells inhibited their differentiation into haploid cells in vitro. Overexpression of Ggnbp2 in Ggnbp2 null but not in Ggn null GC-2spd cells partially rescued the defect coinciding with a restoration of Ggn expression. Together, these data suggest that GGNBP2, likely mediated by its interaction with GGN1, plays a role in DSB repair during meiotic progression of spermatocytes.