Preimplantation development of mouse oocytes activated by different levels of human phospholipase C zeta

Background: A sperm-specific phospholipase C zeta (PLC zeta) has been shown to trigger Ca2+ oscillations in mouse and human oocytes and appears to be the sperm factor responsible for activation at fertilization. Previously, complementary RNA (cRNA) injection was used to introduce PLC zeta into oocytes, but it was unclear how much PLC zeta protein is required for development. Here we have injected cRNA encoding luciferase-tagged human PLC zeta (hPLC zeta-luc) into mouse oocytes and established the relationship between hPLC zeta-luc expression, Ca2+ oscillations and development. Methods: Mouse oocytes were injected with hPLC zeta-luc cRNA and a fluorescent Ca(2+)dye to monitor hPLC zeta-luc expression and Ca2+ oscillations, respectively. After inducing diploidy, development in vitro was monitored in hPLC zeta-luc cRNA microinjected oocytes and compared with parallel oocytes activated by incubation in Sr2+. Results: Repetitive Ca2+ oscillations and oocyte activation were triggered by hPLC zeta over a wide range of luciferase expression levels. However, subsequent development of embryos to the blastocyst stage was observed only when expression of hPLC zeta-luc was optimized within a specific range. The blastocyst cell number was also affected by the level of hPLC zeta expression. Conclusions: Human PLC zeta can readily activate mouse oocytes, however, effective development to blastocyst stages is only achieved within a specific window of hPLC zeta-luc protein expression levels.