Deficiency of theTbc1d21gene causes male infertility with morphological abnormalities of the sperm mitochondria and flagellum in mice

Author summary Male sterility affects one in seven couples, and around half of these are the result of male factor disorders. The common conditions of male infertility cases include reduced sperm motility, low sperm account, and spermatozoa with abnormal morphology. We previously identified TBC1D21 as a sterility-related RabGAP gene from infertile men. However, the in vivo function of TBC1D21 in male fertility remains untested. Here, we createdTbc1d21knockout mice. The knockout males were completely sterile, and had sperm-tail and mitochondria defects. Two interactors of TBC1D21, TOMM20, and DNAH7, may account for the irregular and defective patterns observed inTbc1d21(-/-)mouse sperm tails. From a clinical perspective,TBC1D21transcripts are reduced in sperm from patients exhibiting teratozoospermia. Our results indicate that TBC1D21 plays a critical role in the formation of intact mitochondria, and structure of mammalian sperm. Approximately 2-15% of couples experience infertility, and around half of these cases are attributed to male infertility. We previously identifiedTBC1D21as a sterility-related RabGAP gene derived from infertile men. However, thein vivofunction of TBC1D21 in male fertility remains unclear. Here, we show that loss ofTbc1d21in mice resulted in male infertility, characterized by defects in sperm tail structure and diminished sperm motility. The mitochondria of the sperm-tail had an abnormal irregular arrangement, abnormal diameter, and structural defects. Moreover, the axoneme structure of sperm tails was severely disturbed. Several TBC1D21 interactors were selected via proteomic analysis and functional grouping. Two of the candidate interactors, a subunit protein of translocase in the outer membrane of mitochondria (TOMM20) and an inner arm component of the sperm tail axoneme (Dynein Heavy chain 7, DNAH7), confirmedin vivophysical co-localization with TBC1D21. In addition, TOMM20 and DNAH7 detached and dispersed outside the axoneme inTbc1d21-deficient sperm, instead of aligning with the axoneme. From a clinical perspective, the transcript levels ofTBC1D21in sperm from teratozoospermia cases were significantly reduced when compared with those in normozoospermia. We concluded that TBC1D21 is critical for mitochondrial and axoneme development of mammalian sperm.