PLCζ sequence, protein levels, and distribution in human sperm do not correlate with semen characteristics and fertilization rates after ICSI

Sperm-borne PLC zeta protein induces Ca2+ oscillations in the oocyte and is believed to play a major role during oocyte activation. However, its implication in fertilization failure following ICSI is still debated. We analyzed PLC zeta gene sequence, protein expression level, and localization in both patients with previous failed fertilization by ICSI and sperm donors with proven fertility in order to assess the association of PLC zeta with both sperm characteristics and ability to fertilize. Semen from 15 patients and 13 sperm donors with proven fertility was included in the study. Analysis of the PLC zeta gene sequence, protein expression through Western blot, and protein localization by immunofluorescence were performed. Two patients with total fertilization failure presented mutations in heterozygosis in the PLC zeta gene. Comparison with donor sample sequences displayed comparable SNP allele frequency. Distribution pattern of PLC zeta did not vary significantly between donor and patient samples. Levels of PLC zeta protein in sperm cells showed an interindividual variability both in patient and donor samples. Several SNPs previously reported in infertile patients were also present in fertile men. Failed fertilization occurs even when levels and distribution of PLC zeta protein are within normal range. PLC zeta seems to be a necessary but not sufficient factor in determining the molecular pathway involved in oocyte activation.