PLC? causes Ca(2+) oscillations in mouse eggs by targeting intracellular and not plasma membrane PI(4,5)P(2).

ABSTRACT: Sperm-specific phospholipase C ? (PLC?) activates embryo development by triggering intracellular Ca(2+) oscillations in mammalian eggs indistinguishable from those at fertilization. Somatic PLC isozymes generate inositol 1,4,5-trisphophate-mediated Ca(2+) release by hydrolyzing phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) in the plasma membrane. Here we examine the subcellular source of PI(4,5)P(2) targeted by sperm PLC? in mouse eggs. By monitoring egg plasma membrane PI(4,5)P(2) with a green fluorescent protein-tagged PH domain, we show that PLC? effects minimal loss of PI(4,5)P(2) from the oolemma in contrast to control PLC?1, despite the much higher potency of PLC? in eliciting Ca(2+) oscillations. Specific depletion of this PI(4,5)P(2) pool by plasma membrane targeting of an inositol polyphosphate-5-phosphatase (Inp54p) blocked PLC?1-mediated Ca(2+) oscillations but not those stimulated by PLC? or sperm. Immunolocalization of PI(4,5)P(2), PLC?, and catalytically inactive PLC? (ciPLC?) revealed their colocalization to distinct vesicular structures inside the egg cortex. These vesicles displayed decreased PI(4,5)P(2) after PLC? injection. Targeted depletion of vesicular PI(4,5)P(2) by expression of ciPLC?-fused Inp54p inhibited the Ca(2+) oscillations triggered by PLC? or sperm but failed to affect those mediated by PLC?1. In contrast to somatic PLCs, our data indicate that sperm PLC? induces Ca(2+) mobilization by hydrolyzing internal PI(4,5)P(2) stores, suggesting that the mechanism of mammalian fertilization comprises a novel phosphoinositide signaling pathway.

SUBMITTER: Yu Y 

PROVIDER: S-EPMC3258180 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature