The first step in mammalian fertilization is recognition between the sperm head and the zona pellucida, an extracellular glycoprotein coat surrounding the egg. After binding, sperm undergo the acrosome reaction, which involves fusion between the plasma membrane overlying the sperm head and the apposed membrane of the acrosome, a lysosomal vesicle surrounding the nucleus.
Acrosomal proteases allow the sperm to bore through the zona pellucida and fertilize the egg.
In mice, mERP is expressed exclusively on sperm and in spermatogenic cells. Native mERP is transported to the Golgi complex of late-stage round spermatids and accumulates on the dorsal anterior surface of the heads of differentiated sperm. In collaboration with H. Fox, Department of Neuropharmacology, we recently identified 2 transient sperm antigens that may function as part of the sperm coat. The antigens accumulate on the head of epididymal sperm, precisely where mERP is located, and elute from sperm during capacitation. We propose to isolate and characterize these newly identified antigens and to test whether, by association with mERP, they prevent binding of sperm to the egg before completion of capacitation.