GGNBP2 is necessary for testis morphology and sperm development

Gametogenetin Binding Protein 2 (GGNBP2) was identified as a tumor suppressor and verified as such by several studies. GGNBP2 has also been reported to be essential for pregnancy maintenance via regulation of trophoblast stem cells. Gametogenetin (GGN) is a testicular germ cell-specific gene expressed in adult testes. As a potential GGN1-interacting protein, the role of GGNBP2 in spermatogenesis has not yet been clarified. We generated heterozygous GGNBP2 knockout mice and bred them by intercrossing. We found that among the offspring, homozygous GGNBP2 knockout (KO) mice were present in severely reduced numbers. The GGNBP2 KO pups developed normally, but the male siblings showed dramatically reduced fertility. In these male homozygous GGNBP2 KO mice, the only pathological finding was abnormal morphology of the testes and absence of spermatozoa. In addition, increased apoptosis was observed in the testes of GGNBP2 KO mice. SOX9 staining revealed that SOX9-positive Sertoli cells were absent in the seminiferous tubules. In homozygous mice, proliferating cell nuclear antigen (PCNA)-positive cells were localized in the lumen of the convoluted seminiferous tubules. These results suggest that GGNBP2 plays a key role in spermatogenesis by affecting the morphology and function of SOX9-positive Sertoli cells.