Rescue of failed oocyte activation after ICSI in a mouse model of male factor infertility by recombinant phospholipase Cζ

Artificial oocyte activation to overcome failed fertilization after intracytoplasmic sperm injection (ICSI) in human oocytes typically employs Ca(2+) ionophores to produce a single cytosolic Ca(2+) increase. In contrast, recombinant phospholipase Czeta (PLCζ) causes Ca(2+) oscillations indistinguishable from those occurring during fertilization, but remains untested for its efficacy in a scenario of ICSI fertilization failure. Here, we compare PLCζ with other activation stimuli in a mouse model of failed oocyte activation after ICSI, in which heat-treated sperm are injected into mouse oocytes. We show that increasing periods of 56°C exposure of sperm produces a progressive loss of Ca(2+) oscillations after ICSI. The decrease in Ca(2+) oscillations produces a reduction in oocyte activation and embryo development to the blastocyst stage. We treated such oocytes that failed to activate after ICSI either with Ca(2+) ionophore, or with Sr(2+) media which causes Ca(2+) oscillations, or we injected them with recombinant human PLCζ. All these treatments rescued oocyte activation, although Sr(2+) and PLCζ gave the highest rates of development to blastocyst. When recombinant PLCζ was given to oocytes previously injected with control sperm, they developed normally to the blastocyst stage at rates similar to that after control ICSI. The data suggest that recombinant human PLCζ protein is an efficient means of rescuing oocyte activation after ICSI failure and that it can be effectively used even if the sperm already contains endogenous Ca(2+) releasing activity.