抄録
Several Phospholipase C (PLC) isof orms have been found in male and female mammalian gametes and splicing isoforms of PLCδ4 are predominantly expressed in testis. To understand a physiological function of PLCδ4, we generated PLCδ4 gene-deficient mice. PLCδ4 gene-disrupted male mice either produced few small litters or were sterile. In vivo and in vitro fertilization studies showed that PLCδ4 has a functional role in sperm at the early step of fertilization. We also observed that the calcium transients in eggs associated with fertilization were absent or delayed when we used PLCδ4-/- sperm. PLCδ4-/- sperm were unable to initiate the acrosome reaction, an exocytotic event required for fertilization and induced by interaction with the egg coat, the zona pellucida (ZP) . Next we have monitored Ca2+ responses in single sperm, and we found that the [Ca2+] i increase in response to ZP is absent in PLCδ4-/- sperm. Progesterone, another physiological inducer of the acrosome reaction, failed to induce sustained [Ca2+] i increases in PLCδ-/- sperm and consequently the acrosome reaction was partially inhibited. Calcium imaging studies revealed that the [Ca2+] 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 Ca2+ mechanisms. Furthermore, storeoperated channel (SOC) activity was severely impaired in PLCδ4-/- sperm. These results support that PLCδ4 is an essential protein for calcium mobilization in sperm that drives acrosome reactions.
