Phospholipase C zeta (PLCζ) is a key sperm-borne oocyte-activating factor that triggers Ca2+ oscillations and the subsequent block to polyspermy following gamete fusion. Mutations in PLCZ1, the gene encoding PLCζ, cause male infertility and intracytoplasmic sperm injection (ICSI) fertilization failure; and PLCζ _expression and localization patterns are significantly correlated with ICSI fertilization rate (FR). However, in conventional in vitro fertilization (cIVF), whether and how sperm PLCζ _affects fertilization remain unclear. Herein, we identified one previously reported and two novel PLCZ1 mutations associated with polyspermy in vitro that are characterized by excessive sperm–zona binding and a delay in pronuclei (PN) formation. Immunofluorescence staining and oocyte activation testing revealed that virtually all spermatozoa from patients lacked functional PLCζ _and were thus unable to evoke Ca2+ oscillations. ICSI with an artificial oocyte activation treatment successfully rescued the polyspermic phenotype and resulted in a live birth. Furthermore, we analyzed PLCζ _in an additional 58 males after cIVF treatment in the Reproductive and Genetic Hospital of CITIC-Xiangya (Changsha, China) between February 2019 and January 2022. We found that the proportion of spermatozoa that expressed PLCζ _was positively correlated with both 2PN rate and total FR. The optimal cutoff value below which males were likely to experience low FR (total FR ≤30%) after cIVF was 56.7% for the proportion of spermatozoa expressing PLCζ. Our study expands the mutation and the phenotypic spectrum of PLCZ1 and further suggests that PLCζ _constitutes a promising biomarker for identifying low FRs cases in cIVF due to sperm-related oocyte activation deficiency and that sperm PLCζ _analysis may benefit the wider male population and not only men with ICSI failure.
    
    Keywords: conventional IVF; gene variants; PLCζ; polyspermy

Full Text | PDF |