Molecular cloning, testicular postnatal expression, and oocyte-activating potential of porcine phospholipase Cζ

The molecular mechanism by which sperm triggers Ca2+ oscillation, oocyte activation, and early embryonic development has not been clarified. Recently, oocyte activation has been shown to be induced by sperm-specific phospholipase C zeta (PLC zeta). The ability of PLC zeta to induce oocyte activation is highly conserved across vertebrates. In the present study, porcine PLC zeta cDNA was identified and the nucleotide sequence was determined. The expression pattern of porcine PLC zeta mRNA during the period of postnatal testicular development was shown to be similar to that of mouse PLC zeta. PLC zeta mRNA expression in the pig and mouse was detected only in the testes when the elongated spermatids had differentiated, and was detected from day 96 after birth in the pig. Histological examination of porcine testis during the period of postnatal development revealed the presence of spermatozoa from day 110 after birth. These findings suggest that the synthesis of PLC zeta mRNA starts when spermiogenesis is initiated. Microinjection of porcine PLC zeta complementary RNA into porcine oocytes demonstrated that porcine PLC zeta has the ability to trigger repetitive Ca2+ transients in porcine oocytes similar to that observed during fertilization. It was also found that porcine PLC zeta cRNA has the potential to induce oocyte activation and initiate embryonic development up to the blastocyst stage.