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Roland Abi Nahed, Guillaume Martinez, Jean Pascal Hograindleur, Emilie Le Blévec, Sabine Camugli, Richard Le Boucher, Pierre F Ray, Jessica Escoffier, Eric Schmitt and Christophe Arnoult

For artificial insemination (AI) to be successful, it is essential that sperm delivery be perfectly timed relative to ovulation, as sperm lifespan is limited due to oxidative metabolism induced by capacitation. Extending the window of sperm capacitation could therefore increase sperm lifespan, prolong sperm-fertilizing competence and increase AI efficiency. Hyperpolarization of sperm is a crucial step in capacitation and is induced by activation of the potassium calcium-activated channel subfamily U member 1 (KCNU1, also named Slo3 or KSper). Given the essential role played by KCNU1 in capacitation, this study assessed the impact of its pharmacological inhibition on sperm lifespan. We showed that treatment of murine sperm with sub-micromolar concentrations of clofilium, a specific inhibitor of KCNU1, slowed down capacitation, decreased the rate of acrosome reaction and extended the fertilizing competence of capacitated sperm for 12 h. Clofilium also extended fertilizing competence and motility of bovine-capacitated sperm, and increased the rate of fertilization with sperm capacitated for 24 h by 100%, and the rate of blastocyst formation by 150%. Finally, toxicity experiments showed clofilium to have no impact on sperm DNA and no embryotoxicity at the concentration used to extend sperm lifespan. Our results demonstrate that clofilium prolongs fertilizing competence of aging capacitated sperm in vitro in both rodent and bovine species. To our knowledge, this is the first time the duration of sperm-fertilizing competence is shown to be extended by potassium channels blockers.

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Yunhao Liu, Ling Zhang, Wei Li, Qian Huang, Shuo Yuan, Yuhong Li, Junpin Liu, Shiyang Zhang, Guanglun Pin, Shizhen Song, Pierre F Ray, Christophe Arnoult, Chunghee Cho, Balbina Garcia-Reyes, Uwe Knippschild, Jerome F Strauss III and Zhibing Zhang

Mammalian SPAG6, the orthologue of Chlamydomonas reinhardtii PF16, is a component of the central apparatus of the ‘9 + 2’ axoneme that controls ciliary/flagellar motility, including sperm motility. Recent studies revealed that SPAG6 has functions beyond its role in the central apparatus. Hence, we reexamined the role of SPAG6 in male fertility. In wild-type mice, SPAG6 was present in cytoplasmic vesicles in spermatocytes, the acrosome of round and elongating spermatids and the manchette of elongating spermatids. Spag6-deficient testes showed abnormal spermatogenesis, with abnormalities in male germ cell morphology consistent with the multi-compartment pattern of SPAG6 localization. The armadillo repeat domain of mouse SPAG6 was used as a bait in a yeast two-hybrid screen, and several proteins with diverse functions appeared multiple times, including Snapin, SPINK2 and COPS5. Snapin has a similar localization to SPAG6 in male germ cells, and SPINK2, a key protein in acrosome biogenesis, was dramatically reduced in Spag6-deficient mice which have defective acrosomes. SPAG16L, another SPAG6-binding partner, lost its localization to the manchette in Spag6-deficient mice. Our findings demonstrate that SPAG6 is a multi-functional protein that not only regulates sperm motility, but also plays roles in spermatogenesis in multiple cellular compartments involving multiple protein partners.