Putative sperm fusion protein IZUMO and the role of N-glycosylation

IZUMO is the mouse sperm protein proven to be essential for fusion with eggs. It contains one immunoglobulin-like domain with a conserved glycosylation site within. In the present paper, we produced transgenic mouse lines expressing unglycosylated IZUMO (N204Q-IZUMO) in Izumo1 −/− background. The expression of N204Q-IZUMO rescued the infertile phenotype of IZUMO disrupted mice, indicating glycosylation is not essential for fusion-facilitating activity of IZUMO. The N204Q-IZUMO was produced in testis in comparable amounts to wild-type IZUMO, but the amount of N204Q-IZUMO on sperm was significantly decreased by the time sperm reached the cauda epididymis. These data suggest that glycosylation is not essential for the function of IZUMO, but has a role in protecting it from fragmentation in cauda epididymis.