OUP accepted manuscript

The mammalian sperm factor phospholipase C zeta is critical for early embryo division and pregnancy in humans and mice

STUDY QUESTION

Are sperm phospholipase C zeta (PLCζ) profiles linked to the quality of embryogenesis and pregnancy?

SUMMARY ANSWER

Sperm PLCζ levels in both mouse and humans correlate with measures of ideal embryogenesis whereby minimal levels seem to be required to result in successful pregnancy.

WHAT IS KNOWN ALREADY

While causative factors underlying male infertility are multivariable, cases are increasingly associated with the efficacy of oocyte activation, which in mammals occurs in response to specific profiles of calcium (Ca2+) oscillations driven by sperm-specific PLCζ. Although sperm PLCζ abrogation is extensively linked with human male infertility where oocyte activation is deficient, less is clear as to whether sperm PLCζ levels or localization underlies cases of defective embryogenesis and failed pregnancy following fertility treatment.

STUDY DESIGN, SIZE, DURATION

A cohort of 54 couples undergoing fertility treatment were recruited at the assisted reproductive technology laboratory at the King Faisal Hospital and Research Centre, Riyadh, Kingdom of Saudi Arabia. The recruitment criteria for males was a minimum sperm concentration of 5×106 sperm/ml, while all female patients had to have at least five oocytes. Sperm PLCζ analysis was performed in research laboratories, while semen assessments were performed, and time-lapse morphokinetic data were obtained, in the fertility clinic as part of routine treatment. The CRISPR/Cas9 system was concurrently used to induce indels and single-nucleotide mutations within the Plcζ gene to generate strains of Plcζ mutant mice. Sperm PLCζ was evaluated using immunofluorescence and immunoblotting with an antibody of confirmed consistent specificity against PLCζ.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We evaluated PLCζ profiles in sperm samples from 54 human couples undergoing fertility treatment in the context of time-lapse morphokinetic analysis of resultant embryos, correlating such profiles to pregnancy status. Concurrently, we generated two strains of mutant Plcζ mice using CRISPR/Cas9, and performed IVF with wild type (WT) oocytes and using WT or mutant Plcζ sperm to generate embryos. We also assessed PLCζ status in WT and mutant mice sperm in the context of time-lapse morphokinetic analysis and breeding outcomes.

MAIN RESULTS AND THE ROLE OF CHANCE

A significant (P ≤ 0.05) positive relationship was observed between both PLCζ relative fluorescence and relative density with the times taken for both the second cell division (CC2) (r = 0.26 and r = 0.43, respectively) and the third cell division (S2) (r = 0.26). Examination of localization patterns also indicated significant correlations between the presence or absence of sperm PLCζ and CC2 (r = 0.27 and r = -0.27, respectively; P ≤ 0.025). Human sperm PLCζ levels were at their highest in the ideal times of CC2 (8-12 h) compared to time ranges outside the ideal timeframe (<8 and >12 h) where levels of human sperm PLCζ were lower. Following assignment of PLCζ level thresholds, quantification revealed a significantly higher (P ≤ 0.05) rate of successful pregnancy in values larger than the assigned cut-off for both relative fluorescence (19% vs 40%, respectively) and relative density (8% vs 54%, respectively). Immunoblotting indicated a single band for PLCζ at 74 kDa in sperm from WT mice, while a single band was also observed in sperm from heterozygous of Plcζ mutant mouse sperm, but at a diminished intensity. Immunofluorescent analysis indicated the previously reported (Kashir et al., 2021) fluorescence patterns in WT sperm, while sperm from Plcζ mutant mice exhibited a significantly diminished and dispersed pattern at the acrosomal region of the sperm head. Breeding experiments indicated a significantly reduced litter size of mutant Plcζ male mice compared to WT mice, while IVF-generated embryos using sperm from mutant Plcζ mice exhibited high rates of polyspermy, and resulted in significantly reduced numbers of these embryos reaching developmental milestones.

LIMITATIONS, REASONS FOR CAUTION

The human population examined was relatively small, and should be expanded to examine a larger multi-centre cohort. Infertility conditions are often multivariable, and it was not possible to evaluate all these in human patients. However, our mutant Plcζ mouse experiments do suggest that PLCζ plays a significant role in early embryo development.

WIDER IMPLICATIONS OF THE FINDINGS

We found that minimal levels of PLCζ within a specific range were required for optimal early embryogenesis, correlating with increased pregnancy. Levels of sperm PLCζ below specific thresholds were associated with ineffective embryogenesis and lower pregnancy rates, despite eliciting successful fertilization in both mice and humans. To our knowledge, this represents the first time that PLCζ levels in sperm have been correlated to prognostic measures of embryogenic efficacy and pregnancy rates in humans. Our data suggest for the first time that the clinical utilization of PLCζ may stand to benefit not just a specific population of male infertility where oocyte activation is completely deficient (wherein PLCζ is completely defective/abrogated), but also perhaps the larger population of couples seeking fertility treatment.

STUDY FUNDING/COMPETING INTEREST(S)

J.K. is supported by a faculty start up grant awarded by Khalifa University (FSU-2023-015). This study was also supported by a Healthcare Research Fellowship Award (HF-14-16) from Health and Care Research Wales (HCRW) to J.K., alongside a National Science, Technology, and Innovation plan (NSTIP) project grant (15-MED4186-20) awarded by the King Abdulaziz City for Science and Technology (KACST) for J.K. and A.M.A. The authors declare no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Effect of chemical activators after intracytoplasmic sperm injection (ICSI) on embryo development in alpacas

Low motility and low sperm concentration are characteristics of alpaca semen. Thus, the intracytoplasmic sperm injection (ICSI) technique represents an alternative to improve the reproductive capacity of the male. However, the effect of post-ICSI activation in alpaca is not yet known. The aim of the present study was to compare the effect of chemical activators on alpaca embryo development after ICSI. Alpaca ovaries were collected from a local slaughterhouse and transported to the laboratory. Category I, II and III oocytes were matured for 30 h at 38.5 °C. After ICSI, injected oocytes were randomly divided and activated as follows: i) 5 μM ionomycin for 5 min, ii) 7% ethanol for 4 min, iii) 5 μM ionomycin for 5 min, window period 3 h plus 7% ethanol for 4 min, iv) 5 μM ionomycin for 5 min, window period 3 h, a second ionomycin treatment for 5 min, followed by 1.9 mM 6-DMAP for 3 h, v) 10 mM SrCl2 for 3 h. Culture was carried out for 5 days in SOFaa at 38.5 °C. The cleavage rate was the lowest in the SrCl2 group, morula development was the lowest in the SrCl2 and without activation groups, and blastocyst stage was not different between groups (P<0.05). The rates with SrCl2 were lower in total embryos produced, whereas in transferable embryos they were lower with 2Io/6-DMAP and with SrCl2 (P<0.05). In conclusion, alpaca oocyte activation is more efficient with ionomycin and ethanol to produce transferable embryos.

Novel PLCZ1 mutation caused polyspermy during in vitro fertilization

ABSTRACT

Failure of oocyte activation, including polyspermy and defects in pronuclear (PN) formation, triggers early embryonic developmental arrest. Many studies have shown that phospholipase C zeta 1 (PLCZ1) mutations cause failure of PN formation following intracytoplasmic sperm injection (ICSI); however, whether PLCZ1 mutation is associated with polyspermy during in vitro fertilization (IVF) remains unknown. Whole-exome sequencing (WES) was performed to identify candidate mutations in couples with primary infertility. Sanger sequencing was used to validate the mutations. Multiple PLCZ1-mutated sperm were injected into human and mouse oocytes to explore whether PN formation was induced. Assisted oocyte activation (AOA) after ICSI was performed to overcome the failure of oocyte activation. We identified three PLCZ1 mutations in three patients who experienced polyspermy during IVF cycles, including a novel missense mutation c.1154C>T, p.R385Q. PN formation failure was observed during the ICSI cycle. However, injection of multiple PLCZ1-mutated sperm induced PN formation, suggesting that the Ca2+ oscillations induced by the sperm exceeded the necessary threshold for PN formation. AOA after ICSI enabled normal fertilization, and all patients achieved successful pregnancies. These findings expand the mutational spectrum of PLCZ1 and suggest an important role for PLCZ1 in terms of blocking polyspermy. Furthermore, this study may benefit genetic diagnoses in cases of abnormal fertilization and provide potential appropriate therapeutic measures for these patients with sperm-derived polyspermy.

Phospholipase C Zeta in Human Spermatozoa: A Systematic Review on Current Development and Clinical Application

During fertilization, the fusion of the spermatozoa with the oocytes causes the release of calcium from the oocyte endoplasmatic reticulum. This, in turn, triggers a series of calcium ion (Ca2+) oscillations, a process known as oocyte activation. The sperm-specific factor responsible for oocyte activation is phospholipase C zeta (PLCζ). Men undergoing intracytoplasmic sperm injection (ICSI) with their spermatozoa lacking PLCζ are incapable of generating Ca2+ oscillation, leading to fertilization failure. The immunofluorescence assay is the most used technique to assess the expression and localization of PLCζ and to diagnose patients with reduced/absent ability to activate the oocytes. In these patients, the use of assisted oocyte activation (AOA) technique can help to yield successful ICSI results and shorten the time of pregnancy. However, the production of a stable PLCζ recombinant protein represents a new powerful therapeutic approach to treating individuals with this condition. We aim to conduct a systematic review focusing on the expression, level, and localization of PLCζ, discussing the novel genetic mutation associated with its impairment. In addition, we highlight the benefits of AOA, looking at new and less invasive methods to diagnose and treat cases with PLCζ dysfunction.

Early rescue oocyte activation at 5 h post-ICSI is a useful strategy for avoiding unexpected fertilization failure and low fertilization in ICSI cycles

Introduction

Attempts to artificially activate unfertilized oocytes at 24 h post intracytoplasmic sperm injection (ICSI) have generally resulted in poor outcomes. This study aims to explore a new strategy for early judgement and rescue activation of unfertilized oocytes at 5 h post ICSI to avoid unexpected fertilization failure (UFF) or unexpected low fertilization (ULF) in ICSI cycles.

Methods

Firstly, time-lapse data from 278 ICSI cycles were retrospectively analyzed to establish an indicator for fertilization failure prediction. Secondly, 14 UFF and 20 ULF cycles were enrolled for an observational study, early rescue oocyte activation (EROA) was performed on oocytes without post-ICSI Pb2 extrusion to investigate fertilization efficiency, embryo development and clinical outcomes.

Results

The average time to Pb2 extrusion post-ICSI was 3.03±1.21 h, 95.54% of oocytes had extruded Pb2 before 5 h, and the sensitivity and specificity for monitoring Pb2 extrusion at 5 h by time-lapse imaging to predict fertilization were 99.59% and 99.78%, respectively. Early rescue activation of oocytes with no Pb2 extrusion resulted in acceptable fertilization and embryo developmental outcomes, in terms of the fertilization rate (75.00, 72.99%), 2PN fertilization rate (61.36, 56.93%), good-quality embryo rate (42.59, 50.00%), blastocyst formation rate (48.28, 46.03%), good-quality blastocyst rate (34.48, 33.33%), and oocyte utilization rate (36.36, 27.74%), for both UFF and ULF cycles. The clinical pregnancy, embryo implantation, and early miscarriage rates in the rescue oocyte activation group did not significantly differ from those in the Pb2 extrusion group. Fourteen unexpected fertilization failures and 20 low fertilization ICSI cycles were rescued and resulted in clinical pregnancy rates of 40.00% (4/10) and 57.14% (8/14), respectively.

Conclusions

This study demonstrates that monitoring Pb2 extrusion by time-lapse imaging can accurately predict fertilization outcomes, suggesting that early rescue oocyte activation at 5 h post ICSI is an effective strategy for avoiding unexpected fertilization failure and low fertilization in ICSI cycles.

A DNA Methylation Perspective on Infertility

Infertility affects a significant number of couples worldwide and its incidence is increasing. While assisted reproductive technologies (ART) have revolutionized the treatment landscape of infertility, a significant number of couples present with an idiopathic cause for their infertility, hindering effective management. Profiling the genome and transcriptome of infertile men and women has revealed abnormal gene expression. Epigenetic modifications, which comprise dynamic processes that can transduce environmental signals into gene expression changes, may explain these findings. Indeed, aberrant DNA methylation has been widely characterized as a cause of abnormal sperm and oocyte gene expression with potentially deleterious consequences on fertilization and pregnancy outcomes. This review aims to provide a concise overview of male and female infertility through the lens of DNA methylation alterations.

Good practice recommendations on add-ons in reproductive medicine†

STUDY QUESTION

Which add-ons are safe and effective to be used in ART treatment?

SUMMARY ANSWER

Forty-two recommendations were formulated on the use of add-ons in the diagnosis of fertility problems, the IVF laboratory and clinical management of IVF treatment.

WHAT IS KNOWN ALREADY

The innovative nature of ART combined with the extremely high motivation of the patients has opened the door to the wide application of what has become known as 'add-ons' in reproductive medicine. These supplementary options are available to patients in addition to standard fertility procedures, typically incurring an additional cost. A diverse array of supplementary options is made available, encompassing tests, drugs, equipment, complementary or alternative therapies, laboratory procedures, and surgical interventions. These options share the common aim of stating to enhance pregnancy or live birth rates, mitigate the risk of miscarriage, or expedite the time to achieving pregnancy.

STUDY DESIGN, SIZE, DURATION

ESHRE aimed to develop clinically relevant and evidence-based recommendations focusing on the safety and efficacy of add-ons currently used in fertility procedures in order to improve the quality of care for patients with infertility.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ESHRE appointed a European multidisciplinary working group consisting of practising clinicians, embryologists, and researchers who have demonstrated leadership and expertise in the care and research of infertility. Patient representatives were included in the working group. To ensure that the guidelines are evidence-based, the literature identified from a systematic search was reviewed and critically appraised. In the absence of any clear scientific evidence, recommendations were based on the professional experience and consensus of the working group. The guidelines are thus based on the best available evidence and expert agreement. Prior to publication, the guidelines were reviewed by 46 independent international reviewers. A total of 272 comments were received and incorporated where relevant.

MAIN RESULTS AND THE ROLE OF CHANCE

The multidisciplinary working group formulated 42 recommendations in three sections; diagnosis and diagnostic tests, laboratory tests and interventions, and clinical management.

LIMITATIONS, REASONS FOR CAUTION

Of the 42 recommendations, none could be based on high-quality evidence and only four could be based on moderate-quality evidence, implicating that 95% of the recommendations are supported only by low-quality randomized controlled trials, observational data, professional experience, or consensus of the development group.

WIDER IMPLICATIONS OF THE FINDINGS

These guidelines offer valuable direction for healthcare professionals who are responsible for the care of patients undergoing ART treatment for infertility. Their purpose is to promote safe and effective ART treatment, enabling patients to make informed decisions based on realistic expectations. The guidelines aim to ensure that patients are fully informed about the various treatment options available to them and the likelihood of any additional treatment or test to improve the chance of achieving a live birth.

STUDY FUNDING/COMPETING INTEREST(S)

All costs relating to the development process were covered from ESHRE funds. There was no external funding of the development process or manuscript production. K.L. reports speakers fees from Merck and was part of a research study by Vitrolife (unpaid). T.E. reports consulting fees from Gynemed, speakers fees from Gynemed and is part of the scientific advisory board of Hamilton Thorne. N.P.P. reports grants from Merck Serono, Ferring Pharmaceutical, Theramex, Gedeon Richter, Organon, Roche, IBSA and Besins Healthcare, speakers fees from Merck Serono, Ferring Pharmaceutical, Theramex, Gedeon Richter, Organon, Roche, IBSA and Besins Healthcare. S.R.H. declares being managing director of Fertility Europe, a not-for-profit organization receiving financial support from ESHRE. I.S. is a scientific advisor for and has stock options from Alife Health, is co-founder of IVFvision LTD (unpaid) and received speakers' fee from the 2023 ART Young Leader Prestige workshop in China. A.P. reports grants from Gedeon Richter, Ferring Pharmaceuticals and Merck A/S, consulting fees from Preglem, Novo Nordisk, Ferring Pharmaceuticals, Gedeon Richter, Cryos and Merck A/S, speakers fees from Gedeon Richter, Ferring Pharmaceuticals, Merck A/S, Theramex and Organon, travel fees from Gedeon Richter. The other authors disclosed no conflicts of interest.

DISCLAIMER

This Good Practice Recommendations (GPRs) document represents the views of ESHRE, which are the result of consensus between the relevant ESHRE stakeholders and are based on the scientific evidence available at the time of preparation.ESHRE GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or bedeemedinclusive of all proper methods of care, or be exclusive of other methods of care reasonably directed to obtaining the same results.Theydo not replace the need for application of clinical judgement to each individual presentation, or variations based on locality and facility type.Furthermore, ESHRE GPRs do not constitute or imply the endorsement, or favouring, of any of the included technologies by ESHRE.

Significant differences in efficiency between two commonly used ionophore solutions for assisted oocyte activation (AOA): a prospective comparison of ionomycin and A23187

PURPOSE

Despite the success of ICSI in treating severe male factor infertile patients, total fertilization failure (FF) still occurs in around 1-3% of ICSI cycles. To overcome FF, the use of calcium ionophores has been proposed to induce oocyte activation and restore fertilization rates. However, assisted oocyte activation (AOA) protocols and ionophores vary between laboratories, and the morphokinetic development underlying AOA remains understudied.

METHODS

A prospective single-center cohort study involving 81 in vitro matured metaphase-II oocytes from 66 oocyte donation cycles artificially activated by A23187 (GM508 CultActive, Gynemed) (n=42) or ionomycin (n=39). Parthenogenesis was induced, and morphokinetic parameters (tPNa, tPNf, t2-t8, tSB, and tB) were compared between the 2 study groups and a control group comprising 39 2PN-zygotes from standard ICSI cycles.

RESULTS

Ionomycin treatment resulted in higher activation rates compared to A23187 (38.5% vs 23.8%, p=0.15). Importantly, none of the A23187-activated parthenotes formed blastocysts. When evaluating the morphokinetic dynamics between the two ionophores, we found that tPNa and tPNf were significantly delayed in the group treated by A23187 (11.84 vs 5.31, p=0.002 and 50.15 vs 29.69, p=0.005, respectively). t2 was significantly delayed in A23187-activated parthenotes when compared to the double heterologous control embryo group. In contrast, the morphokinetic development of ionomycin-activated parthenotes was comparable to control embryos (p>0.05).

CONCLUSION

Our results suggest that A23187 leads to lower oocyte activation rates and profoundly affects morphokinetic timings and preimplantation development in parthenotes. Despite our limited sample size and low parthenote competence, standardization and further optimization of AOA protocols may allow wider use and improved outcomes for FF cycles.

Applications of advances in mRNA-based platforms as therapeutics and diagnostics in reproductive technologies

The recent COVID-19 pandemic led to many drastic changes in not only society, law, economics, but also in science and medicine, marking for the first time when drug regulatory authorities cleared for use mRNA-based vaccines in the fight against this outbreak. However, while indeed representing a novel application of such technology in the context of vaccination medicine, introducing RNA into cells to produce resultant molecules (proteins, antibodies, etc.) is not a novel principle. It has been common practice to introduce/inject mRNA into oocytes and embryos to inhibit, induce, and identify several factors in a research context, while such aspects have also been proposed as potential therapeutic and diagnostic applications to combat infertility in humans. Herein, we describe key areas where mRNA-based platforms have thus far represented potential areas of clinical applications, describing the advantages and limitations of such applications. Finally, we also discuss how recent advances in mRNA-based platforms, driven by the recent pandemic, may stand to benefit the treatment of infertility in humans. We also present brief future directions as to how we could utilise recent and current advancements to enhance RNA therapeutics within reproductive biology, specifically with relation to oocyte and embryo delivery.

A new hypothesis may explain human parthenogenesis and ovarian teratoma: A review study

Parthenogenesis (PG) is a rare phenomenon occurring in humans, and understanding this may help us develop an explanation for such occurrences. Moreover, it may help reveal the cause of idiopathic ovarian teratoma (OT). We aim to explain the occurrence of PG and OT in humans based on a new hypothesis. Previous literature has been searched through relevant scientific websites and international journals on the causes and mechanisms of PG and OT in humans. The previous literature on human PG was sparse and mostly contained case reports. It appears that human PG is not as rare as previously reported but may occur spontaneously, resulting in OT formation. The difference between PG and sexual reproduction is that PG has no embryonic diversity. The biopsied embryonic samples in the PG correspond exclusively to those of the maternal side. Spontaneous PG in humans often degrades or leads to formation of OT. The cause and mechanism of spontaneous PG remain unclear in the available literature. Here, we hypothesized that in some cases the secondary oocyte and first polar body enclosed in the zona pellucida may fuse together to form a single cell that restores the diploid number of chromosomes and initiates cell division to form PG. It may go unnoticed or be represented by the OT. Future studies are recommended to investigate this hypothesis.

Total fertilization failure after ICSI: insights into pathophysiology, diagnosis, and management through artificial oocyte activation

BACKGROUND

Total fertilization failure (TFF) is the failure of all metaphase II oocytes to fertilize in ART cycles. The phenomenon represents a known cause of infertility, affecting 1-3% of ICSI cycles. Oocyte activation deficiency (OAD) is the leading cause of fertilization failure, attributed to sperm- or oocyte-related issues, although until recently little attention has been given to oocyte-related deficiencies. Different strategies for overcoming TFF have been proposed in clinical settings, mainly using artificial oocyte activation (AOA) by calcium ionophores. Typically, AOA has been blindly applied with no previous diagnosis testing and, therefore, not considering the origin of the deficiency. The scarcity of data available and the heterogeneous population subjected to AOA make it challenging to draw firm conclusions about the efficacy and safety of AOA treatments.

OBJECTIVE AND RATIONALE

TFF leads to an unexpected, premature termination of ART, which inflicts a substantial psychological and financial burden on patients. This review aims to provide a substantial update on: the pathophysiology of fertilization failure, focusing both on sperm- and oocyte-related factors; the relevance of diagnostic testing to determine the cause of OAD; and the effectiveness and safety of AOA treatments to overcome fertilization failure.

SEARCH METHODS

Relevant studies were identified in the English-language literature using PubMed search terms, including fertilization failure, AOA, phospholipase C zeta (PLCζ), PLCZ1 mutations, oocyte-related factors, wee1-like protein kinase 2 (WEE2) mutations, PAT1 homolog 2 (PATL2) mutations, tubulin beta-8 chain (TUBB8) mutations, and transducin-like enhancer protein 6 (TLE6) mutations. All relevant publications until November 2022 were critically evaluated and discussed.

OUTCOMES

Fertilization failure after ART has been predominantly associated with PLCζ deficiencies in sperm. The reason relates to the well-established inability of defective PLCζ to trigger the characteristic pattern of intracellular Ca2+ oscillations responsible for activating specific molecular pathways in the oocyte that lead to meiosis resumption and completion. However, oocyte deficiencies have recently emerged to play critical roles in fertilization failure. Specifically, mutations have been identified in genes such as WEE2, PATL2, TUBB8, and TLE6. Such mutations translate into altered protein synthesis that results in defective transduction of the physiological Ca2+ signal needed for maturation-promoting factor (MPF) inactivation, which is indispensable for oocyte activation. The effectiveness of AOA treatments is closely related to identifying the causal factor of fertilization failure. Various diagnostic tests have been developed to determine the cause of OAD, including heterologous and homologous tests, particle image velocimetry, immunostaining, and genetic tests. On this basis, it has been shown that conventional AOA strategies, based on inducing the calcium oscillations, are highly effective in overcoming fertilization failure caused by PLCζ-sperm deficiencies. In contrast, oocyte-related deficiencies might be successfully managed using alternative AOA promoters that induce MPF inactivation and meiosis resumption. Such agents include cycloheximide, N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine (TPEN), roscovitine, and WEE2 complementary RNA. In addition, when OAD is caused by oocyte dysmaturity, applying a modified ovarian stimulation protocol and trigger could improve fertilization.

WIDER IMPLICATIONS

AOA treatments represent a promising therapy to overcome fertilization failure caused by sperm- and oocyte-related factors. Diagnosing the cause of fertilization failure will be essential to improve the effectiveness and safe utilization of AOA treatments. Even though most data have not shown adverse effects of AOA on pre- and post-implantation embryo development, the literature is scarce on the matter concerned and recent studies, mainly using mice, suggest that AOA might cause epigenetic alterations in the resulting embryos and offspring. Until more robust data are available, and despite the encouraging results obtained, AOA should be applied clinically judiciously and only after appropriate patient counseling. Currently, AOA should be considered an innovative treatment, not an established one.

The Therapeutic and Diagnostic Potential of Phospholipase C Zeta, Oocyte Activation, and Calcium in Treating Human Infertility

Oocyte activation, a fundamental event during mammalian fertilisation, is initiated by concerted intracellular patterns of calcium (Ca2+) release, termed Ca2+ oscillations, predominantly driven by testis-specific phospholipase C zeta (PLCζ). Ca2+ exerts a pivotal role in not just regulating oocyte activation and driving fertilisation, but also in influencing the quality of embryogenesis. In humans, a failure of Ca2+ release, or defects in related mechanisms, have been reported to result in infertility. Furthermore, mutations in the PLCζ gene and abnormalities in sperm PLCζ protein and RNA, have been strongly associated with forms of male infertility where oocyte activation is deficient. Concurrently, specific patterns and profiles of PLCζ in human sperm have been linked to parameters of semen quality, suggesting the potential for PLCζ as a powerful target for both therapeutics and diagnostics of human fertility. However, further to PLCζ and given the strong role played by Ca2+ in fertilisation, targets down- and up-stream of this process may also present a significantly similar level of promise. Herein, we systematically summarise recent advancements and controversies in the field to update expanding clinical associations between Ca2+-release, PLCζ, oocyte activation and human fertility. We discuss how such associations may potentially underlie defective embryogenesis and recurrent implantation failure following fertility treatments, alongside potential diagnostic and therapeutic avenues presented by oocyte activation for the diagnosis and treatment of human infertility.

Assisted Oocyte Activation following Intracytoplasmic Sperm Injection: A Sensible Option for Infertile Couples with Severe Teratozoospermia

The intracytoplasmic sperm injection (ICSI) has significantly improved male factor infertility treatment; however, complete fertilization failure still occurs in 1-5% of ICSI treatment cycles mainly due to oocyte activation failure. It is estimated that around 40-70% of oocyte activation failure is associated with sperm factors after ICSI. Assisted oocyte activation (AOA) as an effective approach to avoid total fertilization failure (TFF) has been proposed following ICSI. In the literature, several procedures have been described to overcome failed oocyte activation. These include mechanical, electrical, or chemical stimuli initiating artificial Ca²⁺ rises in the cytoplasm of oocytes. AOA in couples with previous failed fertilization and those with globozoospermia has resulted in varying degrees of success. The aim of this review is to examine the available literature on AOA in teratozoospermic men undergoing ICSI-AOA and determine whether the ICSI-AOA should be considered as an adjunct fertility procedure for these patients.

What Does Intracytoplasmic Sperm Injection Change in Embryonic Development? The Spermatozoon Contribution

The intracytoplasmic sperm injection (ICSI) technique was invented to solve severe male infertility due to altered sperm parameters. Nowadays, it is applied worldwide for the treatment of couple infertility. ICSI is performed with any available spermatozoon from surgery or ejaculated samples, whatever are the sperm motility, morphology or quantity. The aim of the present review was to study if embryo development and kinetics would be modified by (1) ICSI under the technical aspects, (2) the micro-injected spermatozoa in connection with male infertility. From published data, it can be seen that ICSI anticipates the zygote kinetics Furthermore, because fertilization rate is higher in ICSI compared to conventional in vitro fertilization (IVF), more blastocysts are obtained for clinical use in ICSI. Sperm and spermatozoa characteristics, such as sperm parameters, morphology and vitality, DNA content (levels of sperm DNA fragmentation, microdeletions, and chromosomal abnormalities), RNA content, epigenetics, and sperm recovery site (testicular, epididymis, and ejaculated), have an impact on fertilization and blastocyst rates and embryo kinetics in different ways. Even though ICSI is the most common solution to solve couples' infertility, the causes of male infertility are crucial in building a competent spermatozoa that will contribute to normal embryonic development and healthy offspring.

Effect of calcium ionophore (A23187) on embryo development and its safety in PGT cycles

Background

Intracytoplasmic sperm injection (ICSI) has tremendous advantages for resolving the problem of male infertility. However, ICSI fertilization can fail in some patients because of various reasons, primarily because of the failure of oocyte activation. Oocytes have been activated using calcium ionophore (A23187) in previous clinical cases of ICSI fertilization failure. However, studies on the efficiency of calcium ionophore (A23187) activation, its effects on the developmental potential of embryos, and its effects on pregnancy outcomes after embryo transfer are relatively limited.

Methods

In this study, we investigated the safety and long-term efficacy of calcium ionophore (A23187) by analyzing its effects on fertilization, embryonic development, aneuploidy, and pregnancy outcomes in patients undergoing preimplantation genetic testing (PGT) cycles.

Results

Comparative analyses of the activation followed by PGT (A-PGT) and PGT groups revealed no significant differences between the oocyte cleavage rate and high-quality embryo rate (98.19% vs. 98.63% and 63.13% vs. 68.39%, respectively, p > 0.05). Although the blastocyst formation rate was significantly lower in the A-PGT group than that in the PGT group (52.22% vs. 59.90%, p < 0.05), no significant difference was observed in the blastocyst aneuploidy rates of the two groups (24.49% vs. 24.55%, p > 0.05). Furthermore, no significant differences were observed between the two groups in terms of the live birth rate (43.75% vs. 52.99%), week of delivery, and birth weight of the infants after transfer of euploid blastocysts (p > 0.05). Furthermore, the 2PN rate, oocyte cleavage rate, blastocyst formation rate, and live birth rate were found to be significantly lower in the A-ICSI group than those in the ICSI group (p < 0.01), but there was no significant difference between the two groups in the week of delivery and birth weight of live births (p > 0.05).

Discussion

These results suggest that the use of calcium ionophore (A23187) activation as an option in cases of ICSI fertilization failure does not affect the ploidy of developing blastocysts and has no significant effects on the week of delivery or birth weight after transfer. Thus, we provide a scientific basis for the clinical safety of oocyte activation using calcium ionophore (A23187).

Artificial oocyte activation using Ca2+ ionophores following intracytoplasmic sperm injection for low fertilization rate

This large multi-center retrospective study examined whether artificial oocyte activation (AOA) using Ca²⁺ ionophore following ICSI improves the live birth rate for couples with previous ICSI cycles of unexplained low fertilization rate. In this large-scale multi-center retrospective study conducted in Japan, data were collected from Keio University and 17 collaborating institutions of the Japanese Institution for Standardizing Assisted Reproductive Technology. Between January 2015 and December 2019, 198 couples were included in this study. Oocytes for both the intervention and control groups were procured from the same pool of couples. Oocytes obtained from ICSI cycles with no or low fertilization rate (<50%) with unknown causes were included in the control (conventional ICSI) group while oocytes procured from ICSI cycles followed by performing AOA were assigned to the intervention (ICSI-AOA) group. Those fertilized with surgically retrieved sperm were excluded. ICSI-AOA efficacy and safety were evaluated by comparing these two groups. Live birth rate was the primary outcome. The ICSI-AOA group (2,920 oocytes) showed a significantly higher live birth per embryo transfer rate (18.0% [57/316]) compared to that of the conventional ICSI group with no or low fertilization rate (1,973 oocytes; 4.7% [4/85]) (odds ratio 4.5, 95% confidence interval 1.6-12.6; P<0.05). A higher live birth rate was observed in younger patients without a history of oocyte retrieval. Miscarriage, preterm delivery, and fetal congenital malformation rates were similar between the two groups. ICSI-AOA may reduce fertilization failure without increasing risks during the perinatal period. AOA may be offered to couples with an ICSI fertilization rate < 50%.

IQCN disruption causes fertilization failure and male infertility due to manchette assembly defect

Total fertilization failure (TFF) is an important cause of infertility; however, the genetic basis of TFF caused by male factors remains to be clarified. In this study, whole-exome sequencing was firstly used to screen for genetic causes of TFF after intracytoplasmic sperm injection (ICSI), and homozygous variants in the novel gene IQ motif-containing N (IQCN) were identified in two affected individuals with abnormal acrosome structures. Then, Iqcn-knockout mice were generated by CRISPR-Cas9 technology and showed that the knockout male mice resembled the human phenotypes. Additionally, we found that IQCN regulates microtubule nucleation during manchette assembly via calmodulin and related calmodulin-binding proteins, which resulted in head deformity with aberrant oocyte activation factor PLCζ. Fortunately, ICSI with assisted oocyte activation can overcome IQCN-associate TFF and male infertility. Thus, our study firstly identified the function of IQCN, highlights the relationship between the manchette assembly and fertilization, and provides a genetic marker and a therapeutic option for male-source TFF.