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

Balbach, Melanie; Hamzeh, Hussein; Jikeli, Jan F; Brenker, Christoph; Schiffer, Christian; Hansen, Jan N; Neugebauer, Pia; Trötschel, Christian; Jovine, Luca; Han, Ling; Florman, Harvey M; Kaupp, U Benjamin; Strünker, Timo; Wachten, Dagmar

Abstract

Mammalian oocytes are enveloped by the zona pellucida (ZP), an extracellular matrix of glycoproteins. In sperm, stimulation with ZP proteins evokes a rapid Ca2+ influx via the sperm-specific, pH-sensitive Ca2+ 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 Ca2+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.