ACTIVATION OF MOUSE SPERM PHOSPHATIDYLINOSITOL-4,5 BISPHOSPHATE-PHOSPHOLIPASE-C BY ZONA-PELLUCIDA IS MODULATED BY TYROSINE PHOSPHORYLATION

Many cellular responses to the occupancy of membrane receptors include the hydrolysis of phosphatidylinositol-4,5 bisphosphate (PIP2) by pho spholipase C (PLC) and the subsequent generation of inositol 1,4,5-tri phosphate (IP3) and diacylglycerol (DAG). In the gamete interaction sy stem, sperm respond to binding to the egg's extracellular matrix, the zona pellucida (zp), by exocytosis of the acrosome in a process known as the acrosome reaction (AR). Under physiological conditions, zp bind ing stimulates ARs only after sperm have undergone a final maturation phase, known as capacitation. One of the zp glycoproteins, ZP3, serves as the ligand for sperm plasma membrane receptors and as the trigger for this regulated exocytosis. Both phosphoinositide-linked and tyrosi ne kinase-mediated pathways participate in the signalling cascade trig gered by sperm-zp interaction. This paper reports that stimulation wit h solubilized zp increased PIP2-PLC enzymatic activity from mouse sper m. ZP3 is the zp component responsible for this stimulation. The effec t was abolished by tyrphostin, suggesting that zp activation of PLC wa s mediated by tyrosine phosphorylation and that gamma was the PLC isof orm involved. We show the presence and distribution of PLC gamma 1 in mouse sperm. Immunostaining studies indicate that PLC gamma 1 is restr icted to the sperm head. Sperm capacitation induced translocation of P LC gamma 1 from the soluble to the particulate fraction. These data su ggest that PLC gamma 1 constitutes a component in the cascade that cou ples sperm binding to the egg's extracellular matrix with acrosomal ex ocytosis, a regulated secretory response upon which fertilization depe nds absolutely. (C) 1996 Wiley-Liss, Inc.