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

BACKGROUND A sperm-specific phospholipase C zeta (PLCζ) 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 PLCζ into oocytes, but it was unclear how much PLCζ protein is required for development. Here we have injected cRNA encoding luciferase-tagged human PLCζ (hPLCζ-luc) into mouse oocytes and established the relationship between hPLCζ-luc expression, Ca2+ oscillations and development. METHODS Mouse oocytes were injected with hPLCζ-luc cRNA and a fluorescent Ca2+dye to monitor hPLCζ-luc expression and Ca2+ oscillations, respectively. After inducing diploidy, development in vitro was monitored in hPLCζ-luc cRNA microinjected oocytes and compared with parallel oocytes activated by incubation in Sr2+. RESULTS Repetitive Ca2+ oscillations and oocyte activation were triggered by hPLCζ over a wide range of luciferase expression levels. However, subsequent development of embryos to the blastocyst stage was observed only when expression of hPLCζ-luc was optimized within a specific range. The blastocyst cell number was also affected by the level of hPLCζ expression. CONCLUSIONS Human PLCζ can readily activate mouse oocytes, however, effective development to blastocyst stages is only achieved within a specific window of hPLCζ-luc protein expression levels