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Is artificial oocyte activation (AOA) effective for patients with unexplained low or no fertilization following IVF/intracytoplasmic sperm injection (ICSI)? All IVF/ICSI cases resulting in total fertilization failure or fertilization rate ≤25% at Ninewells Assisted Conception Unit, Dundee between January 2014 and December 2021 (n = 231) were reviewed contemporaneously. After exclusion of obvious stimulation, egg, sperm and/or assisted reproductive technology laboratory factors, patients with at least one cycle of IVF/ICSI resulting in apparently unexplained fertilization abnormalities were offered research investigations, including sperm immunocytochemistry for phospholipase C zeta (PLCζ) protein expression. This retrospective case–control cohort study evaluated laboratory and clinical outcomes for 39 couples (15 attended for sperm studies research) that subsequently undertook ICSI-AOA with Ca2+ ionophore. Comparing preceding IVF/ICSI and subsequent ICSI-AOA for each patient, the number of eggs collected was similar; however, ICSI-AOA resulted in a significantly improved fertilization rate (57.2% versus 7.1%; P < 0.0001). The uplift for a subset of 10 patients identified with PLCζ deficiency was 66.3% versus 4.6% (P < 0.0001). Overall, ICSI-AOA resulted in a higher number of fresh embryo transfers (94.6% versus 33.3%; P < 0.0001), a significantly higher clinical pregnancy rate (CPR) and live birth rate (LBR; 18.9% versus 2.6%; P = 0.02), a significant increase in cycles with surplus embryos suitable for cryostorage (43.6% versus 0%; P < 0.0001), and increased cumulative CPR (41.0% versus 2.6%; P < 0.0001) and LBR (38.5% versus 2.6%; P < 0.0001). AOA is a powerful tool that can transform clinical outcomes for couples experiencing apparently unexplained fertilization abnormalities. PLCζ assays have the potential to be valuable diagnostic tools to determine patient selection for ICSI-AOA, and research efforts should continue to focus on their development. [ABSTRACT FROM AUTHOR]

Sperm-specific phospholipase C zeta (PLCζ) initiates intracellular calcium (Ca2+) transients which drive a series of concurrent events collectively termed oocyte activation. Numerous investigations have linked abrogation and absence/reduction of PLCζ with forms of male infertility in humans where oocyte activation fails. However, very few studies have examined potential relationships between PLCζ and advancing male age, both of which are increasingly considered to be major effectors of male fertility. Initial efforts in humans may be hindered by inherent PLCζ variability within the human population, alongside a lack of sufficient controllable repeats. Herein, utilizing immunoblotting, immunofluorescence, and quantitative reverse transcription PCR (qRT-PCR) we examined for the first time PLCζ protein levels and localization patterns in sperm, and PLCζ mRNA levels within testes, from mice at 8 weeks, 12 weeks, 24 weeks, and 36 weeks of age, from two separate strains of mice, C57BL/6 (B6; inbred) and CD1 (outbred). Collectively, advancing male age generally diminished levels and variability of PLCζ protein and mRNA in sperm and testes, respectively, when both strains were examined. Furthermore, advancing male age altered the predominant pattern of PLCζ localization in mouse sperm, with younger mice exhibiting predominantly post-acrosomal, and older mice exhibiting both post-acrosomal and acrosomal populations of PLCζ. However, the specific pattern of such decline in levels of protein and mRNA was strain-specific. Collectively, our results demonstrate a negative relationship between advancing male age and PLCζ levels and localization patterns, indicating that aging male mice from different strains may serve as useful models to investigate PLCζ in cases of male infertility and subfertility in humans.

Sperm-specific phospholipase C zeta (PLCζ) is widely considered to be the physiological stimulus responsible for generating calcium (Ca2+) oscillations that induce egg activation and early embryonic development during mammalian fertilization. In the mammalian testis, PLCζ expression is detected at spermiogenesis following elongated spermatid differentiation. Sperm-delivered PLCζ induces Ca2+ release via the inositol 1,4,5-trisphosphate (InsP3) signaling pathway. PLCζ is the smallest known mammalian PLC isoform identified to date, with the simplest domain organization. However, the distinctive biochemical properties of PLCζ compared with other PLC isoforms contribute to its unique potency in stimulating cytosolic Ca2+ oscillations within mammalian eggs. Moreover, studies describing PLCζ “knockout” mouse phenotypes confirm the supreme importance of PLCζ at egg activation and monospermic fertilization in mice. Importantly, a number of clinical reports have highlighted the crucial importance of PLCζ in human fertilization by associating PLCζ deficiencies with certain forms of male factor infertility. Herein, we give an update on recent advances that have refined our understanding of how sperm PLCζ triggers Ca2 + oscillations and egg activation in mammals, while also discussing the nature of a potential “alternative” sperm factor. We summarise PLCζ localization in mammalian sperm, and the direct links observed between defective PLCζ protein in sperm and documented cases of male infertility. Finally, we postulate how this sperm protein can be used as a potential diagnostic marker, and also as a powerful therapeutic agent for treatment of certain types of male infertility due to egg activation failure or even in more general cases of male subfertility.

Background: Artificial oocyte activation (AOA) is a specialized method in assisted reproductive technique (ART). According to increasing concern about using AOA, it is necessary to evaluate sperm-borne oocyte activating factors (SOAFs) including phospholipase C zeta (PLCζ). In this study, PLCζ before AOA was evaluated first and then the impact of AOA on pre-implantation embryo development was investigated. Methods: This prospective clinical trial enrolled couples subjected to ICSI. By evaluating PLCζ, semen samples were categorized into two groups; I (Control) and II (PLCζ deficient). Retrieved oocytes from partners were put into three categories: control group (Injected with sperm from group I, n=113), group without AOA (Injected with sperm from group II and no exposure to AOA, n=106), and group AOA (Injected with sperm from group II and exposure to AOA, n=114). Finally, fertilization results were compared via Kruskal-Wallis followed by Dunn's multiple comparison test. The p<0.05 was considered statistically significant. Results: Fertilization rate was significantly lower in the group without AOA compared to control group (41.9±6.3 vs. 78.1±4.7, p<0.001). AOA improved fertilization rate in group AOA compared to the group without AOA (69.5±3.9 vs. 41.9±6.3, p< 0.01); however, cleavage (91.7±2.8, 90.9±4.6, and 95.2±3.4, respectively) and embryo quality (2.5±0.1, 2.3±0.2, and 2.4±0.2, respectively) scores were not substantially different between groups of control, with and without AOA. Conclusion: We showed that PLCζ can be considered as a good biomarker in evaluation of oocyte activation capability. Further studies are required to establish the best use of PLCζ as a biomarker in clinics. [ABSTRACT FROM AUTHOR]

BACKGROUND Mammalian oocytes are activated by intracellular calcium (Ca2+) oscillations following gamete fusion. Recent evidence implicates a sperm-specific phospholipase C zeta, PLCζ, which is introduced into the oocyte following membrane fusion, as the responsible factor. This review summarizes the current understanding of human oocyte activation failure and describes recent discoveries linking certain cases of male infertility with defects in PLCζ expression and activity. How these latest findings may influence future diagnosis and treatment options are also discussed. METHODS Systematic literature searches were performed using PubMed, ISI-Web of Knowledge and The Cochrane Library. We also scrutinized material from the United Nations and World Health Organization databases (UNWHO) and the Human Fertilization and Embryology Authority (HFEA). RESULTS AND CONCLUSIONS Although ICSI results in average fertilization rates of 70%, complete or virtually complete fertilization failure still occurs in 1–5% of ICSI cycles. While oocyte activation failure can, in some cases, be overcome by artificial oocyte activators such as calcium ionophores, a more physiological oocyte activation agent might release Ca2+ within the oocyte in a more efficient and controlled manner. As PLCζ is now widely considered to be the physiological agent responsible for activating mammalian oocytes, it represents both a novel diagnostic biomarker of oocyte activation capability and a possible mode of treatment for certain types of male infertility. [ABSTRACT FROM PUBLISHER]

Objective: To evaluate the localization of phospholipase C zeta (PLC zeta) in non-capacitated, capacitated, and ionophore-treated sperm.Design: Phospholipase C zeta was cloned from the hamster, an important model organism for studying fertilization. Next, we used hamster and mouse models to investigate the localization of PLC zeta in non-capacitated and capacitated sperm and in sperm treated with ionophore to induce the acrosome reaction.Setting: University laboratory.Animal(s): Male mice and hamsters, 4-6 weeks old.Intervention(s): None.Main Outcome Measure(s): Phospholipase C zeta localization in non-capacitated, capacitated, and ionophore-treated sperm.Result(s): Full-length hamster PLC zeta complementary DNA is 1953 base pairs in size, encoding an open reading frame of 651 amino acids, sharing 85% amino acid similarity with the mouse. Phospholipase C zeta was localized in acrosomal and post-acrosomal regions of sperm. The post-acrosomal localization, which became more evident after capacitation and was maintained after ionophore treatment, is in line with PLC zeta being the endogenous agent of egg activation. However, the acrosomal PLC zeta population, which was lost after ionophore treatment, suggests that PLC zeta could have other functions besides egg activation.Conclusion(s): Phospholipase C zeta is localized to acrosomal and post-acrosomal regions and undergoes dynamic changes during capacitation and the acrosome reaction, indicating a potential role regulating not only egg activation but other sperm functions. [ABSTRACT FROM AUTHOR]

Objective: To use in vivo gene transfer into the testis by electroporation to express a fluorescent recombinant form of a testis-specific gene in the mature epididymal sperm of mice and thus study the pattern of gene localization.Design: Controlled animal study.Setting: Research laboratory at the University of Oxford.Animal(s): Four- to 6-week-old male mice.Intervention(s): Phospholipase C zeta (PLCzeta), the putative mammalian egg activation factor, was fused to enhanced yellow fluorescent protein (EYFP), and in vivo gene transfer by electroporation was used to introduce this transgene (PLCzeta-EYFP) into mouse testis. Transgene expression in testis and sperm were analyzed at 20 and 40 days after electroporation.Main Outcome Measure(s): Transgene expression in testis and epididymal sperm was analyzed by fluorescence microscopy and an excitation light source suitable for EYFP.Result(s): Phospholipase C zeta-EYFP was successfully expressed in epididymal sperm when analyzed 40 days after gene transfer and was localized to the head and midpiece regions.Conclusion(s): Our results provide the first demonstration that in vivo gene transfer can be used to study the localization of proteins in mature sperm and that this represents a powerful new technique for studying male infertility and gene function in sperm. [ABSTRACT FROM AUTHOR]