The pattern of localization of the putative oocyte activation factor, phospholipase Cζ, in uncapacitated, capacitated, and ionophore-treated human spermatozoa

BACKGROUND: Recent studies suggest that in mammals, oocyte activation at fertilization is triggered by a sperm-specific phospholipase C, PLC zeta. We investigated PLC zeta localization in human spermatozoa. METHODS: A polyclonal antibody was generated against human PLC zeta and used in immunoblotting and immunofluorescence studies of ejaculated human sperm in uncapacitated and capacitated states. An ionophore was also used to induce the acrosome reaction in vitro. RESULTS: After verifying specificity of the anti-PLC zeta antibody by immunoblotting, immunofluorescence studies showed that the predominant localization of PLC zeta in uncapacitated sperm was in the equatorial region, a pattern maintained following capacitation and ionophore treatment. The analysis of pooled samples showed similar to 88% of uncapacitated sperm expressed PLC zeta in the equatorial region, whereas similar to 35% and similar to 21% of sperm expressed additional populations of PLC zeta in the acrosomal or post-acrosomal region, respectively. One population of PLC zeta was observed in the post-acrosomal region of similar to 12% of sperm. The proportion of cells with post-acrosomal PLC zeta increased following capacitation and ionophore treatment (P < 0.05). The same tendency was found in individual samples. There was a strong correlation (r = 0.716, P < 0.0001) between presence of an intact acrosome and proportion of sperm immunoreactive to PLC zeta in the acrosomal region. CONCLUSIONS: PLC zeta was variably detectable in three localities within the sperm head: the equatorial segment and acrosomal/post-acrosomal region. Variability in PLC zeta localization in sperm from fertile males may reflect differences in oocyte activation capabilities between individuals or within an ejaculate. This approach may help in investigating the possible links between PLC zeta and certain types of male infertility.