The role of calcium-mobilizing signal transduction system in fertilization

点击翻译按钮获取中文摘要

Zona-Pellucida(ZP)-induced acrosome reaction in sperm is a required step for mammalian fertilization. However, the precise mechanism of the acrosome reaction remains unclear. We previously reported that Phospholipase C delta 4 (PLCδ4) is involved in ZP-induced acrosome reaction in mouse sperm. Here we have monitored Ca^<2+> responses in single sperm, and we report that the [Ca^<2+>]_i increase in response to ZP, which is essential for driving the acrosome reaction in vivo, is absent in PLCδ4^<-/-> sperm. Progesterone, another physiological inducer of the acrosome reaction, failed to induce sustained [Ca^<2+>]_i increases in PLCδ4^<-/-> sperm and consequently the acrosome reaction was partially inhibited. In addition, we observed oscillative [Ca^<2+>]_i increases in wild-type sperm in response to these acrosome inducers. Calcium imaging studies revealed that the [Ca^<2+>]_i increases induced by exposure to ZP and progesterone started at different sites within the sperm head, indicating that these agonists induce the acrosome reaction via different Ca^<2+> mechanisms. Furthermore, store-operated channel (SOC) activity was severely impaired in PLCδ4^<-/-> sperm. These results indicate that PLCδ4 is an important enzyme for intracellular [Ca^<2+>]_i mobilization in ZP-induced acrosome reaction and for sustained [Ca^<2+>]_i increases through SOC induced by ZP and progesterone in sperm.