Rat DCST1 and DCST2 are essential for sperm–egg fusion

Abstract Physiological functions of fertilization-related genes in male fertility differ among species. The sperm membrane proteins, DC-STAMP domain containing (DCST) 1 and 2, are essential for male fertility in mice and zebrafish. Although dcst2 knockout (KO) zebrafish sperm showed impaired binding to the oolemma, mouse Dcst2 KO sperm showed impaired fusion after binding to the oolemma. Thus, the physiological functions of the target genes must be analyzed in various genetically modified animals. In this study, the physiological function of DCST1/2 in male fertility was examined in Dcst1/2 double-KO (dKO) rats. Dcst1/2 dKO male rats were completely infertile in mating tests, which was consistent with the phenotypes observed in Dcst1/2 dKO mice and zebrafish. The motility and acrosome reaction of Dcst1/2 dKO rat sperm were similar to those of control sperm. Dcst1/2 dKO sperm accumulated in the perivitelline space of eggs collected from females after natural mating, similar to izumo sperm–egg fusion 1 (Izumo1) KO rat sperm. Sperm lacking either Dcst1/2 or Izumo1 were incubated with zona pellucida-free eggs in vitro. Izumo1 KO sperm showed impaired sperm–egg binding. IZUMO1 remained in Dcst1/2 dKO sperm, and Dcst1/2 dKO sperm after the acrosome reaction could bind to, but not fuse with the oolemma. Rat DCST1/2 is essential for sperm–egg fusion, which is consistent with the function of mouse DCST1/2. Phylogenetic analyses showed that human DCST1/2 was closer to mouse and rat DCST1/2 than to zebrafish Dcst1/2. The role of DCST1/2 in sperm–egg fusion is therefore widely conserved in mammals.