Molecular Mechanism Underlying the Action of Zona-pellucida Glycoproteins on Mouse Sperm

Mammalian oocytes are enveloped by the zona pellucida (ZP), an extracellular matrix of glycoproteins. In sperm, stimulation with ZP proteins evokes a rapid Ca(2+) influx via the sperm-specific, pH-sensitive Ca(2+) channel CatSper. However, the physiological role and molecular mechanisms underlying ZP-dependent activation of CatSper are unknown. Here, we delineate the sequence of ZP-signaling events in mouse sperm. We show that ZP proteins evoke a rapid intracellular pH(i) increase that rests predominantly on Na(+)/H(+) exchange by NHA1 and requires cAMP synthesis by the soluble adenylyl cyclase sAC as well as a sufficiently negative membrane potential set by the spem-specific K(+) channel Slo3. The alkaline-activated CatSper channel translates the ZP-induced pH(i) increase into a Ca(2+) response. Our findings reveal the molecular components underlying ZP action on mouse sperm, opening up new avenues for understanding the basic principles of sperm function and, thereby, mammalian fertilization.