Mammalian phospholipase Cζ induces oocyte activation from the sperm perinuclear matrix

Abstract

Mammalian sperm-borne oocyte activating factor (SOAF) induces oocyte activation from a compartment that engages the oocyte cytoplasm, but it is not known how. A SOAF-containing extract (SE) was solubilized from the submembrane perinuclear matrix, a domain that enters the egg. SE initiated activation sufficient for full development. Microinjection coupled to tandem mass spectrometry enabled functional correlation profiling of fractionated SE without a priori assumptions about its chemical nature. Phospholipase C-zeta (PLCζ) correlated absolutely with activating ability. Immunoblotting confirmed this and showed that the perinuclear matrix is the major site of 72-kDa PLCζ. Oocyte activation was efficiently induced by 1.25 fg of sperm PLCζ, corresponding to a fraction of one sperm equivalent (∼0.03). Immunofluorescence microscopy localized sperm head PLCζ to a post-acrosomal region that becomes rapidly exposed to the ooplasm following gamete fusion. This multifaceted approach suggests a mechanism by which PLCζ originates from an oocyte-penetrating assembly—the sperm perinuclear matrix—to induce mammalian oocyte activation at fertilization.