Deletion of Eqtn in mice reduces male fertility and sperm–egg adhesion

: A number of sperm proteins are involved in the processes from gamete adhesion to fusion, but the underlying mechanism is still unclear. Here, we established a mouse mutant, the EQUATORIN-knockout (EQTN-KO, Eqtn−/−) mouse model and found that the EQTN-KO males have reduced fertility and sperm–egg adhesion, while the EQTN-KO females are fertile. Eqtn−/− sperm were normal in morphology and motility. Eqtn−/−-Tg (Acr-Egfp) sperm, which were produced as the acrosome reporter by crossing Eqtn−/− with Eqtn+/+-Tg(Acr-Egfp) mice, traveled to the oviduct ampulla and penetrated the egg zona pellucida of WT females. However, Eqtn−/− males mated with WT females showed significant reduction in both fertility and the number of sperm attached to the zona-free oocyte. Sperm IZUMO1 and egg CD9 behaved normally in Eqtn−/− sperm when they were fertilized with WT egg. Another acrosomal protein, SPESP1, behaved aberrantly in Eqtn−/− sperm during the acrosome reaction. The fertility impairment of EQTN/SPESP1-double KO males lacking Eqtn and Spesp1 (Eqtn/Spesp1−/−) was more severe compared with that of Eqtn−/− males. Eqtn−/−-Tg (Eqtn) males, which were generated to rescue Eqtn−/−males, restored the reduced fertility.