Starting a new life: sperm PLC-zeta mobilizes the Ca2+ signal that induces egg activation and embryo development: an essential phospholipase C with implications for male infertility.
ABSTRACT We have discovered that a single sperm protein, phospholipase C-zeta (PLCζ), can stimulate intracellular Ca(2+) signalling in the unfertilized oocyte ('egg') culminating in the initiation of embryonic development. Upon fertilization by a spermatozoon, the earliest observed signalling event in the dormant egg is a large, transient increase in free Ca(2+) concentration. The fertilized egg responds to the intracellular Ca(2+) rise by completing meiosis. In mammalian eggs, the Ca(2+) signal is delivered as a train of long-lasting cytoplasmic Ca(2+) oscillations that begin soon after gamete fusion and persist beyond the completion of meiosis. Sperm PLCζ effects Ca(2+) release from egg intracellular stores by hydrolyzing the membrane lipid PIP(2) and consequent stimulation of the inositol 1,4,5-trisphosphate (InsP(3) ) receptor Ca(2+) -signalling pathway, leading to egg activation and early embryogenesis. Recent advances have refined our understanding of how PLCζ induces Ca(2+) oscillations in the egg and also suggest its potential dysfunction as a cause of male infertility.
Dataset: Phospholipase Cz rescues failed oocyte activation in a prototype of male factor infertility[show abstract] [hide abstract]
ABSTRACT: Objective: To determine the effect of infertility-linked sperm phospholipase Cz (PLCz) mutations on their ability to trigger oocyte Ca 2þ oscillations and development, and also to evaluate the potential therapeutic utility of wild-type, recombinant PLCz protein for rescuing failed oocyte activation and embryo development. Design: Test of a novel therapeutic approach to male factor infertility. Setting: University medical school research laboratory. Patient(s): Donated unfertilized human oocytes from follicle reduction. Intervention(s): Microinjection of oocytes with recombinant human PLCz protein or PLCz cRNA and a Ca 2þ -sensitive fluorescent dye. Main Outcome Measure(s): Measurement of the efficacy of mutant and wild-type PLCz-mediated enzyme activity, oocyte Ca 2þ oscillations, activation, and early embryo development. Result(s): In contrast to the wild-type protein, mutant forms of human sperm PLCz display aberrant enzyme activity and a total failure to activate unfertilized oocytes. Subsequent microinjection of recombinant human PLCz protein reliably triggers the characteristic pattern of cytoplasmic Ca 2þ oscillations at fertilization, which are required for normal oocyte activation and successful embryo development to the blastocyst stage. Conclusion(s): Dysfunctional sperm PLCz cannot trigger oocyte activation and results in male factor infertility, so a potential thera-peutic approach is oocyte microinjection of active, wild-type PLCz protein. We have demonstrated that recombinant human PLCz can phenotypically rescue failed activation in oocytes that express dysfunctional PLCz, and that this intervention culminates in efficient blastocyst formation.