The roles of Ca2+, downstream protein kinases, and oscillatory signaling in regulating fertilization and the activation of development

Roles of the EF-hand domain of PLCZ1 in establishing species-specific Ca2+ oscillations in mouse and rat fertilization†

Periodic increases in cytosolic calcium concentration (Ca2+ oscillations) during mammalian fertilization induce all the events collectively known as egg activation. The sperm-specific phospholipase C, Phospholipase C zeta 1 (PLCZ1) represents the "sperm factor" vital for initiating the persistent Ca2+ oscillations in mammals. Despite sequence conservation, the Ca2+ oscillation-inducing properties of the enzyme differ vastly among species, and this is particularly salient between mouse and rat PLCZ1, where the activities vary at least one order of magnitude in favor of the former. As previously shown, injecting wild-type rat Plcz1 mRNA into metaphase II mouse eggs induced delayed Ca2+ oscillations with low specific activity compared to the homologous mouse Plcz1 mRNA. We, therefore, sought to uncover the factor(s) diversifying these enzymes by swapping functional domains between species, creating chimeric PLCZ1s. When injected into mouse metaphase II eggs, mouse Plcz1 mRNA with the whole- or part of the EF-hand domains swapped with the rat showed a substantial reduction in activity compared to WT. Consistently, the opposite exchange enhanced the rat's enzyme activity. EF-hand domains 1 and 2 seemed to underlie most differences, and mutations of the divergent amino acids within these domains, substitutions for Glu(m-30; r-29) and Gln(m-58; r-57), changed the activity of both species' PLCZ1s in opposite directions. Collectively, our findings support the view that differences in the sequences of EF-hand domains, especially in several of its charged residues, underpin the distinct PLCZ1 activities between these species, revealing the gametes and species' adaptability to optimize the fertilization signal and early development.

No transcription, no problem: Protein phosphorylation changes and the transition from oocyte to embryo

Although mature oocytes are arrested in a differentiated state, they are provisioned with maternally-derived macromolecules that will start embryogenesis. The transition to embryogenesis, called 'egg activation', occurs without new transcription, even though it includes major cell changes like completing stalled meiosis, translating stored mRNAs, cytoskeletal remodeling, and changes to nuclear architecture. In most animals, egg activation is triggered by a rise in free calcium in the egg's cytoplasm, but we are only now beginning to understand how this induces the egg to transition to totipotency and proliferation. Here, we discuss the model that calcium-dependent protein kinases and phosphatases modify the phosphorylation landscape of the maternal proteome to activate the egg. We review recent phosphoproteomic mass spectrometry analyses that revealed broad phospho-regulation during egg activation, both in number of phospho-events and classes of regulated proteins. Our interspecies comparisons of these proteins pinpoints orthologs and protein families that are phospho-regulated in activating eggs, many of which function in hallmark events of egg activation, and others whose regulation and activity warrant further study. Finally, we discuss key phospho-regulating enzymes that may act apically or as intermediates in the phosphorylation cascades during egg activation. Knowing the regulators, targets, and effects of phospho-regulation that cause an egg to initiate embryogenesis is crucial at both fundamental and applied levels for understanding female fertility, embryo development, and cell-state transitions.

Assessing the impact of calcium ionophore on pregnancy outcomes in artificial oocyte activation cycles: a 10-year update of systematic review and meta-analysis

PURPOSE

The objective is to evaluate the effectiveness and safety of calcium ionophore as an artificial oocyte activation (AOA) method on pregnancy outcomes in different groups of intracytoplasmic sperm injection (ICSI) patients, providing potential evidence to establish consensus on the indications of AOA.

METHODS

A systematic comprehensive search was performed in Medline, Embase, the Cochrane Library, and Google Scholar databases. Studies published from January 2014 to June 2024 were searched for analysis. All studies that compared ICSI with AOA-ICSI in routine indications composing impaired fertilization or embryo developmental arrest in previous cycles, or male-factor infertility were included.

RESULTS

Twelve studies were included in the meta-analysis. AOA-ICSI was associated with the increase in the overall fertilization rate (OR 1.99, 95% CI 1.16-3.41) and live birth rate (OR 4.58, 95% CI 1.52-13.80). All secondary outcomes including cleavage, blastocyst, high-quality embryo, implantation, biochemical pregnancy, clinical pregnancy presented superiority or equivalence in AOA-ICSI. And the use of calcium ionophore did not increase the miscarriage rate (OR 0.43, 95% CI 0.08-2.43). In subgroup analysis, AOA-ICSI exhibited a more significant effect on patients with indications of no or low fertilization. However, in patients with non-fertilization factors, no statistically significant improvements were observed in all outcomes.

CONCLUSION

Calcium ionophore is an effective artificial oocyte activation approach to improving pregnancy outcomes after ICSI, particularly in cases with indications of fertilization factors, providing further support for the application of AOA in specific populations. Further validation is needed to comprehensively establish the safety of AOA.

TRIAL REGISTRATION

PROSPERO registration number CRD42024551481.

Septins as key players in spermatogenesis, fertilisation and pre-implantation embryogenic cytoplasmic dynamics

Septins are a family of cytokinesis-related proteins involved in regulating cytoskeletal design, cell morphology, and tissue morphogenesis. Apart from cytokinesis, as a fourth component of cytoskeleton, septins aid in forming scaffolds, vesicle sorting and membrane stability. They are also known to be involved in the regulation of intracellular calcium (Ca2+) via the STIM/Orai complex. Infertility affects ~ 15% of couples globally, while male infertility affects ~ 7% of men. Global pregnancy and live birth rates following fertility treatment remain relatively low, while there has been an observable decline in male fertility parameters over the past 60 years. Low fertility treatment success can be attributed to poor embryonic development, poor sperm parameters and fertilisation defects. While studies from the past few years have provided evidence for the role of septins in fertility related processes, the functional role of septins and its related complexes in cellular processes such as oocyte activation, fertilization, and sperm maturation are not completely understood. This review summarizes the available knowledge on the role of septins in spermatogenesis and oocyte activation via Ca2+ regulation, and cytoskeletal dynamics throughout pre-implantation embryonic development. We aim to identify the currently less known mechanisms by which septins regulate these immensely important mechanisms with a view of identifying areas of investigation that would benefit our understanding of cell and reproductive biology, but also provide potential avenues to improve current methods of fertility treatment.

Transcriptome analysis of porcine oocytes during postovulatory aging

Decreased oocyte quality is a significant contributor to the decline in female fertility that accompanies aging in mammals. Oocytes rely on mRNA stores to support their survival and integrity during the protracted period of transcriptional dormancy as they await ovulation. However, the changes in mRNA levels and interactions that occur during porcine oocyte maturation and aging remain unclear. In this study, the mRNA expression profiles of porcine oocytes during the GV, MII, and aging (24 h after the MII stage) stages were explored by transcriptome sequencing to identify the key genes and pathways that affect oocyte maturation and postovulatory aging. The results showed that 10,929 genes were coexpressed in porcine oocytes during the GV stage, MII stage, and aging stage. In addition, 3037 genes were expressed only in the GV stage, 535 genes were expressed only in the MII stage, and 120 genes were expressed only in the aging stage. The correlation index between the GV and MII stages (0.535) was markedly lower than that between the MII and aging stages (0.942). A total of 3237 genes, which included 1408 upregulated and 1829 downregulated genes, were differentially expressed during porcine oocyte postovulatory aging (aging stage vs. MII stage). Key functional genes, including ATP2A1, ATP2A3, ATP2B2, NDUFS1, NDUFA2, NDUFAF3, SREBF1, CYP11A1, CYP3A29, GPx4, CCP110, STMN1, SPC25, Sirt2, SYCP3, Fascin1/2, PFN1, Cofilin, Tmod3, FLNA, LRKK2, CHEK1/2, DDB1/2, DDIT4L, and TONSL, and key molecular pathways, such as the calcium signaling pathway, MAPK signaling pathway, TGF-β signaling pathway, PI3K/Akt signaling pathway, FoxO signaling pathway, gap junctions, and thermogenesis, were found in abundance during porcine postovulatory aging. These genes are mainly involved in the regulation of many biological processes, such as oxidative stress, calcium homeostasis, mitochondrial function, and lipid peroxidation, during porcine oocyte postovulatory aging. These results contribute to a more in-depth understanding of the biological changes, key regulatory genes and related biological pathways that are involved in oocyte aging and provide a theoretical basis for improving the efficiency of porcine embryo production in vitro and in vivo.

Efficiency of the zinc chelator 1,10-phenanthroline for assisted oocyte activation following ICSI in pigs

Context In vitro embryo production in pigs is an important tool for advancing biomedical research. Intracytoplasmic sperm injection (ICSI) circumvents the polyspermy problems associated with conventional IVF in porcine. However, the suboptimal efficiency for ICSI in pigs requires new strategies to increase blastocyst formation rates. Aim To investigate novel methods for assisted activation using the zinc chelator 1,10-phenanthroline (PHEN), and to improve embryo developmental competence and quality of ICSI porcine blastocyst. Methods ICSI embryos were treated with PHEN after or before sperm injection, recording pronuclear formation, blastocyst rate and the expression of SMARCA4, OCT4, SOX2 and CDX2. Key results Neither electrical nor PHEN significantly improves pronuclear formation rates before or after ICSI. Following in vitro culture to the blastocyst stage, no significant differences were observed in developmental rates among the groups. Moreover, the use of PHEN did not alter the total cell number or the expression of OCT4, SOX2 and CDX2 in pig ICSI blastocysts. Conclusions Assisted oocyte activation with PHEN does not affect the preimplantation development of ICSI-derived pig embryos. Implications These results hold significance in refining and advancing the application of assisted oocyte activation techniques. They offer insights into addressing fertility issues and propelling advancements in human and animal reproductive medicine.

Chemical activation of mammalian oocytes and its application in camelid reproductive biotechnologies: A review

Mammalian oocyte activation is a critical process occurring post-gamete fusion, marked by a sequence of cellular events initiated by an upsurge in intracellular Ca2+. This surge in calcium orchestrates the activation/deactivation of specific kinases, leading to the subsequent inactivation of MPF and MAPK activities, alongside PKC activation. Despite various attempts to induce artificial activation using distinct chemical compounds as Ca2+ inducers and/or Ca2+-independent agents, the outcomes have proven suboptimal. Notably, incomplete suppression of MPF and MAPK activities persists, necessitating a combination of different agents for enhanced efficiency. Moreover, the inherent specificity of activation methods for each species precludes straightforward extrapolation between them. Consequently, optimization of protocols for each species and for each technique, such as PA, ICSI, and SCNT, is required. Despite recent strides in camelid biotechnologies, the field has seen little advancement in chemical activation methods. Only a limited number of chemical agents have been explored, and the effects of many remain unknown. In ICSI, despite obtaining blastocysts with different chemical compounds that induce Ca2+ and calcium-independent increases, viable offspring have not been obtained. However, SCNT has exhibited varying outcomes, successfully yielding viable offspring with a reduced number of chemical activators. This article comprehensively reviews the current understanding of the physiological activation of oocytes and the molecular mechanisms underlying chemical activation in mammals. The aim is to transfer and apply this knowledge to camelid reproductive biotechnologies, with emphasis on chemical activation in PA, ICSI, and SCNT.

Novel PLCZ1 mutation caused polyspermy during in vitro fertilization

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 Ca 2+ 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.

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.

Maternal and obstetric outcomes following the transfer of embryos warmed with fatty acid-supplemented solutions

BACKGROUND

Vitrification procedures decrease intracytoplasmic lipid content and impair developmental competence. Adding fatty acids (FAs) to the warming solution has been shown to recover the lipid content of the cytoplasm and improve developmental competence and pregnancy outcomes. However, the influence of the FA supplementation on live birth rates after embryo transfers and perinatal outcomes remains unknown. In the present study, we examined the influence of FA-supplemented warming solutions on live birth rates, pregnancy complications, and neonatal outcomes after single vitrified-warmed cleavage-stage embryo transfers (SVCTs).

METHODS

The clinical records of 701 treatment cycles in 701 women who underwent SVCTs were retrospectively analyzed. Vitrified embryos were warmed using solutions (from April 2022 to June 2022, control group) or FA-supplemented solutions (from July 2022 to September 2022, FA group). The live birth rate, pregnancy complications, and perinatal outcomes were compared between the control and FA groups.

RESULTS

The live birth rate per transfer was significantly higher in the FA group than in the control group. Multivariate logistic regression analysis further demonstrated a higher probability of live births in the FA group than in the control group. Miscarriage rates, the incidence and types of pregnancy complications, the cesarean section rate, gestational age, incidence of preterm delivery, birth length and weight, incidence of low birth weight, infant sex, and incidence of birth defects were all comparable between the control and FA groups. Multivariate logistic regression analysis further demonstrated no adverse effects of FA-supplemented warming solutions.

CONCLUSIONS

FA-supplemented warming solutions improved live birth rates after SVCTs without exerting any adverse effects on maternal and obstetric outcomes. Therefore, FA-supplemented solutions can be considered safe and effective for improving clinical outcomes and reducing patient burden.

Fatty acid supplementation during warming improves pregnancy outcomes after frozen blastocyst transfers: a propensity score-matched study

This study aimed to examine the viability of human blastocysts after warming with fatty acids (FAs) using an in vitro outgrowth model and to assess pregnancy outcomes after a single vitrified-warmed blastocyst transfer (SVBT). For the experimental study, we used 446 discarded vitrified human blastocysts donated for research purposes by consenting couples. The blastocysts were warmed using FA-supplemented (FA group) or non-FA-supplemented (control group) solutions. The outgrowth area was significantly larger in the FA group (P = 0.0428), despite comparable blastocyst adhesion rates between the groups. Furthermore, the incidence of outgrowth degeneration was significantly lower in the FA group than in the control group (P = 0.0158). For the clinical study, we retrospectively analyzed the treatment records of women who underwent SVBT in natural cycles between January and August 2022. Multiple covariates that affected the outcomes were used for propensity score matching as follows: 1342 patients in the FA group were matched to 2316 patients in the control group. Pregnancy outcomes were compared between the groups. The rates of implantation, clinical pregnancy, and ongoing pregnancy significantly increased in the FA group after SVBTs (P = 0.0091-0.0266). These results indicate that warming solutions supplemented with FAs improve blastocyst outgrowth and pregnancy outcomes after SVBTs.

Fluoride disrupts intestinal epithelial tight junction integrity through intracellular calcium-mediated RhoA/ROCK signaling and myosin light chain kinase

Fluoride is a common contaminant of groundwater and agricultural commodity, which poses challenges to animal and human health. A wealth of research has demonstrated its detrimental effects on intestinal mucosal integrity; however, the underlying mechanisms remain obscure. This study aimed to investigate the role of the cytoskeleton in fluoride-induced barrier dysfunction. After sodium fluoride (NaF) treatment of the cultured Caco-2 cells, both cytotoxicity and cytomorphological changes (internal vacuoles or massive ablation) were observed. NaF lowered transepithelial electrical resistance (TEER) and enhanced paracellular permeation of fluorescein isothiocyanate dextran 4 (FD-4), indicating Caco-2 monolayers hyperpermeability. In the meantime, NaF treatment altered both the expression and distribution of the tight junction protein ZO-1. Fluoride exposure increased myosin light chain II (MLC2) phosphorylation and triggered actin filament (F-actin) remodeling. While inhibition of myosin II by Blebbistatin blocked NaF-induced barrier failure and ZO-1 discontinuity, the corresponding agonist Ionomycin had effects comparable to those of fluoride, suggesting that MLC2 serves as an effector. Given the mechanisms upstream of p-MLC2 regulation, further studies demonstrated that NaF activated RhoA/ROCK signaling pathway and myosin light chain kinase (MLCK), strikingly increasing the expression of both. Pharmacological inhibitors (Rhosin, Y-27632 and ML-7) reversed NaF-induced barrier breakdown and stress fiber formation. The role of intracellular calcium ions ([Ca²⁺]_i) in NaF effects on Rho/ROCK pathway and MLCK was investigated. We found that NaF elevated [Ca²⁺]_i, whereas chelator BAPTA-AM attenuated increased RhoA and MLCK expression as well as ZO-1 rupture, thus, restoring barrier function. Collectively, abovementioned results suggest that NaF induces barrier impairment via Ca²⁺-dependent RhoA/ROCK pathway and MLCK, which in turn triggers MLC2 phosphorylation and rearrangement of ZO-1 and F-actin. These results provide potential therapeutic targets for fluoride-induced intestinal injury.

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.

Successful Production of Offspring Derived from Phospholipase C Zeta-Deficient Sperm by Additional Artificial Activation

During mammalian fertilization, repetitive rises of intracellular calcium called calcium oscillations are required for full activation of oocytes. Therefore, oocytes such as round spermatid injected or somatic cell nuclear transferred require additional artificial activation which mimics the calcium oscillations. It is well recognized that sperm specific phospholipase C (PLCζ) is a strong candidate as the sperm factor which can induce calcium oscillations and, at least in mammals, the genetic mutation of PLCζ in human causes male infertility due to the lack of calcium oscillations in the oocytes. Recent studies showed that the sperm lacking PLCζ (Plcz1^-/-) still could induce rise(s) of intracellular calcium in the oocytes after IVF but not intracytoplasmic sperm injection (ICSI). In the ICSI oocytes, no pronuclear formation or development to the two-cell stage was observed. However, it is still unclear whether additional activation treatment can rescue the low developmental ability of Plcz1^-/--sperm-derived oocytes after ICSI. In this study, we examined whether oocytes injected with a Plcz1^-/- sperm can develop to term by additional artificial activation. In oocytes injected a Plcz1^-/- sperm and Plcz1^-/- and eCS (another candidate of the sperm factor) double knockout sperm (Plcz1^-/-eCS^-/-), the rates of pronuclear formation were very low (2.0 ± 2.3% and 6.1 ± 3.7%, respectively) compared to control (92.1 ± 2.6%). However, these rates were dramatically improved by additional procedures of PLCζ-mRNA injection or SrCl₂ treatment (Plcz1^-/- sperm + PLCζ mRNA, Plcz1^-/- sperm + SrCl₂ and Plcz1^-/-eCS^-/- sperm + PLCζ mRNA; 64.2 ± 10.8%, 89.2 ± 2.4% and 72.6 ± 5.4%, respectively). Most of the oocytes were developed to the two-cell stage. After embryo transfer, healthy pups were obtained in all these groups (Plcz1^-/- sperm + PLCζ mRNA:10.0 ± 2.8%, Plcz1^-/- sperm + SrCl₂:4.0 ± 4.3% and Plcz1^-/-eCS^-/- sperm + PLCζ mRNA: 10.0 ± 5.7%). The rate in Plcz1^-/- sperm + SrCl₂ group was significantly lower than that in control (26.0 ± 2.4%). Taken together, our present results show that additional activation treatment such as SrCl₂ and PLCζ mRNA can fully support to develop to term even in oocyte injected Plcz1^-/- sperm. In addition, PLCζ-induced oocyte activation is more suitable for successful development to term compared to that such as phenomenon induced by SrCl₂. These findings will contribute to improvement for male-dependent human infertility and reproductive technologies in other mammalian species.

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.

Reorganization, specialization, and degradation of oocyte maternal components for early development

Background

Oocyte components are maternally provided, solely determine oocyte quality, and coordinately determine embryo quality with zygotic gene expression. During oocyte maturation, maternal organelles are drastically reorganized and specialized to support oocyte characteristics. A large number of maternal components are actively degraded after fertilization and gradually replaced by zygotic gene products. The molecular basis and the significance of these processes on oocyte/embryo quality are not fully understood.

Methods

Firstly, recent findings in organelle characteristics of other cells or oocytes from model organisms are introduced for further understanding of oocyte organelle reorganization/specialization. Secondly, recent progress in studies on maternal components degradation and their molecular mechanisms are introduced. Finally, future applications of these advancements for predicting mammalian oocyte/embryo quality are discussed.

Main findings

The significance of cellular surface protein degradation via endocytosis for embryonic development, and involvement of biogenesis of lipid droplets in embryonic quality, were recently reported using mammalian model organisms.

Conclusion

Identifying key oocyte component characteristics and understanding their dynamics may lead to new applications in oocyte/embryo quality prediction and improvement. To implement these multidimensional concepts, development of new technical approaches that allow us to address the complexity and efficient studies using model organisms are required.

Fatty acid supplementation into warming solutions improves pregnancy outcomes after single vitrified-warmed cleavage stage embryo transfers

Purpose

This study aimed to examine the embryonic development of human 4-cell stage embryos after warming with fatty acids (FAs) and to assess the pregnancy outcomes after single vitrified-warmed cleavage stage embryo transfers (SVCTs).

Methods

Experimental study: A total of 217 discarded, vitrified human 4-cell stage embryos donated for research by consenting couples were used. The embryos were warmed using the fatty acid (FA)-supplemented solutions (FA group) or nonsupplemented solutions (control group). The developmental rate, morphokinetics, and outgrowth competence were analyzed. Clinical study: The treatment records of women undergoing SVCT in natural cycles between April and September 2022 were retrospectively analyzed (April-June 2022, control group; July-September 2022, FA group).

Results

Experimental study: The rate of morphologically good blastocysts was significantly higher in the FA group than in the control group (p = 0.0302). The morphokinetics during cleavage, morula, and blastocyst stages were comparable between the groups. The outgrowth was significantly increased in the FA group (p = 0.0438). Clinical study: The rates of implantation, clinical pregnancy, and ongoing pregnancy after SVCTs were significantly increased in the FA group (p = 0.0223-0.0281).

Conclusions

Fatty acid-supplemented warming solutions effectively improve embryo development to the blastocyst stage and pregnancy outcomes after SVCTs.

Embryo development and live birth resulted from artificial oocyte activation after microdissection testicular sperm extraction with ICSI in patients with non-obstructive azoospermia

INTRODUCTION

The application of microdissection testicular sperm extraction (micro-TESE) to retrieve the sperm of patients with non-obstructive azoospermia (NOA) has greatly increased. Patients with NOA often have poor quality sperm. Unfortunately, there are few studies on artificial oocyte activation (AOA) performed on patients who successfully retrieved motile and immotile sperm by micro-TESE after intracytoplasmic sperm injection (ICSI). Therefore, this study sought to obtain more comprehensive evidence-based data and embryo development outcomes to aid consultation of patients with NOA who opted to receive assisted reproductive techniques and to determine whether AOA needs to be performed in different motile sperm after ICSI.

METHODS

This retrospective study involved 235 patients with NOA who underwent micro-TESE to retrieve adequate sperm for ICSI between January 2018 and December 2020. A total of 331 ICSI cycles were performed in the 235 couples. Embryological, clinical, and neonatal outcomes were demonstrated comprehensively between motile sperm and immotile sperm using AOA and non-AOA treatment.

RESULTS

Motile sperm injection with AOA (group 1) showed significantly higher fertility rate (72.77% vs. 67.59%, p=0.005), 2 pronucleus (2PN) fertility rate (64.33% vs. 60.22%, p=0.036), and miscarriage rate (17.65% vs. 2.44%, p=0.018) compared with motile sperm injection with non-AOA (group 2). Group 1 had comparable available embryo rate (41.29% vs. 40.74%, p=0.817), good embryo rate (13.44% vs. 15.44%, p=0.265), and without an embryo for transfer rate (10.85% vs. 9.90%, p=0.815) compared with group 2. Immotile sperm injection with AOA (group 3) displayed significantly higher fertility rate (78.56% vs. 67.59%, p=0.000), 2PN fertility rate (67.36% vs. 60.22%, p=0.001), without an embryo for transfer rate (23.76% vs. 9.90%, p=0.008), and miscarriage rate (20.00% vs. 2.44%, p=0.014), but significantly lower available embryo rate (26.63% vs.40.74%, p=0.000) and good embryo rate (15.44% vs. 6.99%, p=0.000) compared with group 2. In groups 1, 2, and 3, the rates of implantation (34.87%, 31.85% and 28.00%, respectively; p=0.408), clinical pregnancy (43.87%, 41.00%, and 34.48%, respectively; p=0.360) and live birth (36.13%, 40.00%, and 27.59%, respectively; p=0.194) were similar.

DISCUSSION

For those patients with NOA from whom adequate sperm were retrieved for ICSI, AOA could improve fertilization rate, but not embryo quality and live birth outcomes. For patients with NOA and only immotile sperm, AOA can help achieve acceptable fertilization rate and live birth outcomes. AOA is recommended for patients with NOA only when immotile sperm are injected.

Sperm Energy Restriction and Recovery (SER) Alters Epigenetic Marks during the First Cell Cycle of Development in Mice

The sperm energy restriction and recovery (SER) treatment developed in our laboratory was shown to improve fertilization and blastocyst development following in vitro fertilization (IVF) in mice. Here, we investigated the effects of SER on early embryogenesis. Developmental events observed during the first cell cycle indicated that progression through the pronuclear stages of SER-generated embryos is advanced in comparison with control-generated embryos. These findings prompted further analysis of potential effects of SER on pronuclear chromatin dynamics, focusing on the key H3K4me3 and H3K27ac histone modifications. Nearly all the SER-generated embryos displayed H3K4me3 in the male pronuclei at 12 h post-insemination (HPI), while a subset of the control-generated embryos did not. Additionally, SER-generated embryos displayed a more homogenous intensity of H3K27ac at 8 and 12 HPI compared to control embryos. These changes in histone modifications during the first cell cycle were accompanied by differences in gene expression at the two-cell stage; both of these changes in early embryos could potentially play a role in the improved developmental outcomes of these embryos later in development. Our results indicate that sperm incubation conditions have an impact on early embryo development and can be useful for the improvement of assisted reproductive technology outcomes.

Is there any effect on imprinted genes H19, PEG3, and SNRPN during AOA?

Assisted oocyte activation (AOA) has been proposed as an effective technique to overcome the problem of impaired fertilization after intracytoplasmic sperm injection (ICSI) but the safety of AOA remains a concern. We aimed to investigate if AOA induces imprinting effects on embryos. We used 13 cleavage embryos, nine blastocysts, and eight placentas from 15 patients. The subjects were divided into six groups by tissue type and with or without AOA. The methylation levels of imprinted genes (H19, paternally expressed gene [PEG3] and small nuclear ribonucleoprotein polypeptide N [SNRPN]) were tested by pyrosequencing. We observed different methylation levels among cleavage embryos. The variability was much more remarkable between cleavage embryos than blastocysts and placenta tissues. The methylation levels were especially higher in SNRPN and lower in the H19 gene in AOA embryos than those without AOA. No significant difference was found either among blastocysts or among placenta tissues regardless of AOA. The methylation levels of the three genes in blastocysts were very similar to those in the placenta. Compared to conventional ICSI, AOA changed imprinting methylation rates at H19 and SNRPN in cleavage embryos but not in the blastocyst stage and placenta. We recommend that blastocyst transfer should be considered for patients undergoing AOA during in vitro fertilization.

OUP accepted manuscript

BACKGROUND

Oocyte activation deficiency (OAD) is attributed to the majority of cases underlying failure of ICSI cycles, the standard treatment for male factor infertility. Oocyte activation encompasses a series of concerted events, triggered by sperm-specific phospholipase C zeta (PLCζ), which elicits increases in free cytoplasmic calcium (Ca²⁺) in spatially and temporally specific oscillations. Defects in this specific pattern of Ca²⁺ release are directly attributable to most cases of OAD. Ca²⁺ release can be clinically mediated via assisted oocyte activation (AOA), a combination of mechanical, electrical and/or chemical stimuli which artificially promote an increase in the levels of intra-cytoplasmic Ca²⁺. However, concerns regarding safety and efficacy underlie potential risks that must be addressed before such methods can be safely widely used.

OBJECTIVE AND RATIONALE

Recent advances in current AOA techniques warrant a review of the safety and efficacy of these practices, to determine the extent to which AOA may be implemented in the clinic. Importantly, the primary challenges to obtaining data on the safety and efficacy of AOA must be determined. Such questions require urgent attention before widespread clinical utilization of such protocols can be advocated.

SEARCH METHODS

A literature review was performed using databases including PubMed, Web of Science, Medline, etc. using AOA, OAD, calcium ionophores, ICSI, PLCζ, oocyte activation, failed fertilization and fertilization failure as keywords. Relevant articles published until June 2019 were analysed and included in the review, with an emphasis on studies assessing large-scale efficacy and safety.

OUTCOMES

Contradictory studies on the safety and efficacy of AOA do not yet allow for the establishment of AOA as standard practice in the clinic. Heterogeneity in study methodology, inconsistent sample inclusion criteria, non-standardized outcome assessments, restricted sample size and animal model limitations render AOA strictly experimental. The main scientific concern impeding AOA utilization in the clinic is the non-physiological method of Ca²⁺ release mediated by most AOA agents, coupled with a lack of holistic understanding regarding the physiological mechanism(s) underlying Ca²⁺ release at oocyte activation.

LIMITATIONS, REASONS FOR CAUTION

The number of studies with clinical relevance using AOA remains significantly low. A much wider range of studies examining outcomes using multiple AOA agents are required.

WIDER IMPLICATIONS

In addition to addressing the five main challenges of studies assessing AOA safety and efficacy, more standardized, large-scale, multi-centre studies of AOA, as well as long-term follow-up studies of children born from AOA, would provide evidence for establishing AOA as a treatment for infertility. The delivery of an activating agent that can more accurately recapitulate physiological fertilization, such as recombinant PLCζ, is a promising prospect for the future of AOA. Further to PLCζ, many other avenues of physiological oocyte activation also require urgent investigation to assess other potential physiological avenues of AOA.

STUDY FUNDING/COMPETING INTERESTS

D.G. was supported by Stanford University’s Bing Overseas Study Program. J.K. was supported by a Healthcare Research Fellowship Award (HF-14-16) made by Health and Care Research Wales (HCRW), 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). The authors have no competing interests to declare.

Dynamic changes of intracellular zinc ion level during maturation, fertilization, activation, and development in mouse oocytes

Although it is well known that calcium oscillations are required for fertilization in all mammalian species studied to date, recent studies also showed the ejection of zinc into the extracellular milieu in a series of coordinated events, called "zinc spark," during mammalian fertilization. These results led us to the hypothesis that a zinc ion-dependent signal is important for oocyte maturation, fertilization (activation), and further embryonic development. In this study, we evaluated the amounts and localization of intracellular zinc ions during maturation, fertilization, activation, and embryonic development in mouse oocytes. Our results show that abundant zinc ions are present in both immature and mature oocytes. After in vitro fertilization, the amounts of zinc ions were dramatically decreased at the pronuclear (PN) stage. Artificial activation by cycloheximide, SrCl₂ , and TPEN also reduced the amounts of zinc ions in the PN stage. On the other hand, PN embryos derived from sperm injection still showed high level of zinc ions. However, the amounts of zinc ions rapidly increased at the blastocysts regardless of activation method. We showed here that the amounts of zinc ions dramatically changed during maturation, fertilization, activation, and development in mouse oocytes.

Design of novel oocyte activation methods: The role of zinc

Oocyte activation occurs at the time of fertilization and is a series of cellular events initiated by intracellular Ca2+ increases. Consequently, oocytes are alleviated from their arrested state in meiotic metaphase II (MII), allowing for the completion of meiosis. Oocyte activation is also an essential step for somatic cell nuclear transfer (SCNT) and an important tool to overcome clinical infertility. Traditional artificial activation methods aim to mimic the intracellular Ca2+ changes which occur during fertilization. Recent studies emphasize the importance of cytoplasmic Zn2+ on oocyte maturation and the completion of meiosis, thus suggesting artificial oocyte activation approaches that are centered around the concentration of available Zn2+in oocytes. Depletion of intracellular Zn2+ in oocytes with heavy metal chelators leads to successful oocyte activation in the absence of cellular Ca2+ changes, indicating that successful oocyte activation does not always depends on intracellular Ca2+ increases. Current findings lead to new approaches to artificially activate mammalian oocytes by reducing available Zn2+ contents, and the approaches improve the outcome of oocyte activation when combined with existing Ca2+ based oocyte activation methods. Here, we review the important role of Ca2+ and Zn2+ in mammalian oocyte activation and development of novel oocyte activation approaches based on Zn2+ availability.

DNA methylation and gene expression changes in mouse pre- and post-implantation embryos generated by intracytoplasmic sperm injection with artificial oocyte activation

BACKGROUND

The application of artificial oocyte activation (AOA) after intracytoplasmic sperm injection (ICSI) is successful in mitigating fertilization failure problems in assisted reproductive technology (ART). Nevertheless, there is no relevant study to investigate whether AOA procedures increase developmental risk by disturbing subsequent gene expression at different embryonic development stages.

METHODS

We used a mouse model to explore the influence of AOA treatment on pre- and post-implantation events. Firstly, the developmental potential of embryos with or without AOA treatment were assessed by the rates of fertilization and blastocyst formation. Secondly, transcriptome high-throughput sequencing was performed among the three groups (ICSI, ICSI-AOA and dICSI-AOA groups). The hierarchical clustering and Principal Component Analysis (PCA) analysis were used. Subsequently, Igf2r/Airn methylation analysis were detected using methylation-specific PCR sequencing following bisulfite treatment. Finally, birth rate and birth weight were examined following mouse embryo transfer.

RESULTS

The rates of fertilization and blastocyst formation were significantly lower in oocyte activation-deficient sperm injection group (dICSI group) when compared with the ICSI group (30.8 % vs. 84.4 %, 10.0 % vs. 41.5 %). There were 133 differentially expressed genes (DEGs) between the ICSI-AOA group and ICSI group, and 266 DEGs between the dICSI-AOA group and ICSI group. In addition, the imprinted gene, Igf2r is up regulated in AOA treatment group compared to control group. The Igf2r/Airn imprinted expression model demonstrates that AOA treatment stimulates maternal allele-specific mehtylation spreads at differentially methylated region 2, followed by the initiation of paternal imprinted Airn long non-coding (lnc) RNA, resulting in the up regulated expression of Igf2r. Furthermore, the birth weight of newborn mice originating from AOA group was significantly lower compared to that of ICSI group. The pups born following AOA treatment did not show any other abnormalities during early development. All offspring mated successfully with fertile controls.

CONCLUSIONS

AOA treatment affects imprinted gene Igf2r expression and mehtylation states in mouse pre- and post-implantation embryo, which is regulated by the imprinted Airn. Nevertheless, no significant differences were found in post-natal growth of the pups in the present study. It is hoped that this study could provide valuable insights of AOA technology in assisted reproduction biology.

ASTL is mutated in female infertility

Female infertility is a relatively common phenotype with a growing number of single gene causes although these account for only a minority of cases. Here, we report a consanguineous family in which adult females who are homozygous for a truncating variant in ASTL display markedly reduced fertility in a pattern strikingly similar to Astl^-/- female mice. ASTL encodes ovastacin, which is known to trigger zona pellucida hardening (ZPH) as part of the cortical reaction upon fertilization. ZPH is required for normal early embryonic development and its absence can be caused by pathogenic variants in other zona pellucida proteins that result in a similar infertility phenotype in humans and mouse. This is the first report of ASTL-related infertility in humans and suggests that the inclusion of ASTL in female infertility gene panels is warranted.

Optimal Treatment of 6-Dimethylaminopurine Enhances the In Vivo Development of Canine Embryos by Rapid Initiation of DNA Synthesis

Artificial activation of oocytes is an important step for successful parthenogenesis and somatic cell nuclear transfer (SCNT). Here, we investigated the initiation of DNA synthesis and in vivo development of canine PA embryos and cloned embryos produced by treatment with 1.9 mM 6-dimethylaminopurine (6-DMAP) for different lengths of time. For experiments, oocytes for parthenogenesis and SCNT oocytes were cultured for 4 min in 10 μM calcium ionophore, and then divided into 2 groups: (1) culture for 2 h in 6-DMAP (DMAP-2h group); (2) culture for 4 h in DMAP (DMAP-4h group). DNA synthesis was clearly detected in all parthenogenetic (PA) embryos and cloned embryos incorporated BrdU 4 h after activation in DMAP-2h and DMAP-4h groups. In vivo development of canine parthenogenetic fetuses was observed after embryo transfer and the implantation rates of PA embryos in DMAP-2h were 34%, which was significantly higher than those in DMAP-4h (6.5%, p < 0.05). However, in SCNT, there was no significant difference in pregnancy rate (DMAP-2h: 41.6% vs. DMAP-4h: 33.3%) and implantation rates (DMAP-2h: 4.94% vs. DMAP-4h: 3.19%) between DMAP-2h and DMAP-4h. In conclusion, the use of DMAP-2h for canine oocyte activation may be ideal for the in vivo development of PA zygotes, but it was not more effective in in vivo development of canine reconstructed SCNT oocytes. The present study demonstrated that DMAP-2h treatment on activation of canine parthenogenesis and SCNT could effectively induce the onset of DNA synthesis during the first cell cycle.

Zinc exocytosis is sensitive to myosin light chain kinase inhibition in mouse and human eggs

Zinc dynamics are essential for oocyte meiotic maturation, egg activation, and preimplantation embryo development. During fertilisation and egg activation, the egg releases billions of zinc atoms (Zn2+) in an exocytotic event termed the 'zinc spark'. We hypothesised that this zinc transport and exocytosis is dependent upon the intracellular trafficking of cortical granules (CG) which requires myosin-actin-dependent motors. Treatment of mature mouse and human eggs with ML-7, a myosin light chain kinase inhibitor (MLCK), resulted in an 80% reduction in zinc spark intensity compared to untreated controls when activated with ionomycin. Moreover, CG migration towards the plasma membrane was significantly decreased in ML-7-treated eggs compared with controls when activated parthenogenetically with ionomycin. In sperm-induced fertilisation via intracytoplasmic sperm injection (ICSI), ML-7-treated mouse eggs exhibited decreased labile zinc intensity and cortical CG staining. Collectively, these data demonstrate that ML-7 treatment impairs zinc release from both murine and human eggs after activation, demonstrating that zinc exocytosis requires myosin light chain kinase activity. Further, these results provide additional support that zinc is likely stored and released from CGs. These data underscore the importance of intracellular zinc trafficking as a crucial component of egg maturation necessary for egg activation and early embryo development.

Effects of fatty acid supplementation during vitrification and warming on the developmental competence of mouse, bovine and human oocytes and embryos

RESEARCH QUESTION

Does fatty acid supplementation in vitrification and warming media influence developmental competence in oocytes after vitrification and warming?

DESIGN

Mouse oocytes and four-cell embryos were vitrified and warmed with solutions supplemented with fatty acid and cultured to the blastocyst stage. To study lipid metabolism after vitrification, quantitative real-time polymerase chain reaction was used to analyse the expression of genes related to beta oxidation in mouse embryos vitrified and warmed with or without fatty acids. The effects of fatty acid supplementation in the warming solutions on the developmental competence of bovine and human embryos were analysed. Blastocyst outgrowth assay was used to evaluate the potential of human blastocysts for adhesion to fibronectin.

RESULTS

The neutral lipid content of mouse oocytes in the fatty acid 1% supplementation group was significantly higher than in the fatty acid 0% group (P = 0.0032). The developmental rate to the blastocyst stage was significantly higher in the fatty acid 1% group than in the fatty acid 0% group in mice (P = 0.0345). Fatty acid supplementation in warming solution upregulated Acaa2 and Hadha in mouse embryos. Fatty acids significantly improved the developmental ability of bovine embryos to the blastocyst stage (P = 0.0048). Warming with 1% fatty acid supplementation significantly increased the proportion of human blastocysts with morphological grade A inner cell mass (P = 0.0074) and trophectoderm (P = 0.0323).

CONCLUSIONS

Fatty acid supplementation in the warming solutions improved the developmental competence of vitrified-warmed mouse oocytes by activating the beta-oxidation pathway. Fatty acid supplementation enhanced the developmental rate of bovine embryos to the blastocyst stage and improved morphological characteristics of human embryos vitrified at the cleavage stage.

Treatment of in vitro-Matured Bovine Oocytes With Tauroursodeoxycholic Acid Modulates the Oxidative Stress Signaling Pathway

In several species, oocyte and embryo competence are improved by the addition of endoplasmic reticulum (ER) stress inhibitors to in vitro maturation (IVM) medium and/or in vitro culture (IVC) medium. This study aimed to evaluate the effects of three concentrations of tauroursodeoxycholic acid (TUDCA; 50, 200, and 1,000 μM), a chemical chaperone for relieving ER stress, during IVM of bovine cumulus-oocyte complexes (COCs) for 24 h. Treated oocytes were analyzed for nuclear maturation, reactive oxygen species (ROS) production, mitochondrial activity, and abundance of target transcripts. In addition, the number of pronuclei in oocytes was evaluated after 18-20 h of insemination, and the rates of blastocyst and hatched blastocyst formation were evaluated after 7 and 8/9 days of culture, respectively. We further evaluated the transcript abundance of embryonic quality markers. Our findings showed that supplementation of IVM medium with 200 μM of TUDCA decreased ROS production and increased abundance of transcripts related to antioxidant activity in oocytes (CAT, GPX1, and HMOX1) and embryos (GPX1 and PRDX3). Interestingly, high concentration of TUDCA (1,000 μM) was toxic to oocytes, reducing the nuclear maturation rate, decreasing mitochondrial activity, and increasing the abundance of ER stress (HSPA5) and cellular apoptosis (CASP3 and CD40) related transcripts. The results of this study suggest that treatment with 200 μM of TUDCA is associated with a greater resistance to oxidative stress and indirectly with ER stress relief in bovine oocytes.

Calcium Ionophore (A23187) Rescues the Activation of Unfertilized Oocytes After Intracytoplasmic Sperm Injection and Chromosome Analysis of Blastocyst After Activation

Calcium is a crucial factor in regulating the biological behavior of cells. The imbalance of calcium homeostasis in cytoplasm will cause abnormal behavior of cells and the occurrence of diseases. In intracytoplasmic sperm injection (ICSI) cycle, the dysfunction of oocyte activation caused by insufficient release of Ca²⁺ from endoplasmic reticulum is one of the main reasons for repeated fertilization failure. Calcium ionophore (A23187) is a highly selective calcium ionophore, which can form stable complex with Ca²⁺ and pass through the cell membrane at will, effectively increasing intracellular Ca²⁺ levels. It has been reported that calcium ionophore (A23187) can activate oocytes and obtain normal embryos. However, there are few studies on unfertilized oocytes after calcium ionophore (A23187) rescue activation in ICSI cycle. The purpose of this study was to analyze the effects of calcium ionophore (A23187) rescue activation on the activation of unfertilized oocytes, embryonic development potential, embryonic development timing and chromosomal aneuploidy, and to compare and analyze the clinical data of patients with calcium ionophore (A23187) activation in clinical application. The results showed that a certain proportion of high-quality blastocysts with normal karyotype could be obtained after calcium ionophore (A23187) rescue activation of unfertilized oocytes, and it did not have a significant effect on the timing of embryo development. In clinical practice, direct activation with calcium ionophore (A23187) after ICSI was better than rescue activation the next day. In conclusions, the studies on the effectiveness and safety of calcium ionophore (A23187) rescue activation for oocytes with ICSI fertilization failure can enable some patients to obtain usable, high-quality embryos during the first ICSI cycle.

Treatment with Calcium Ionophore Improves The Results in Patients with Previous Unsuccessful Attempts at The Fertilization: A Cohort Study

BACKGROUND

The objective of this study is to evaluate artificial oocyte activation (AOA) with calcium ionophore (CaI) in a subsequent attempt at fertilisation in patients after extremely low or failed fertilisation. We assessed improvements in fertilisation, implantation and pregnancy rates as well as cancellation rates in these patients. Finally, was evaluated the result testing in addition to delivery rate and obstetric outcomes in children born after AOA.

MATERIALS AND METHODS

This was a retrospective observational study conducted in an IVF laboratory of an IVI clinic (IVIRMA Valencia, Spain). One group (509 mature oocytes from 66 patients) received a first intracytoplasmic sperm injection (ICSI) without AOA, which resulted in either a failed fertilisation or very low values (<30%). This group was compared with a second group (616 mature oocytes from the same 66 patients) that used AOA. Outcome was compared by McNemar's test and the dependent t tests.

RESULTS

AOA plus CaI resulted in enhanced fertilisation (51 vs. 13.1%), ongoing pregnancy (47 vs. 21.7%), and implantation (31.1 vs. 13.1%) rates, and less chances for cancelling the cycle (22.7 vs. 69.3%). There were no observed adverse effects in obstetric and perinatal outcomes after the use of AOA.

CONCLUSION

Our findings support the use of AOA for a given population of patients where fertilisation was affected during previous attempts. After AOA, we observed a significant increase in reproductive success due to the increased number of embryos available for embryo selection and, therefore, enhanced chances for success. The use of this artificial technique is comforting after checking non-existence of detrimental effects on the offspring.

Diagnosis and Treatment of Male Infertility-Related Fertilization Failure

Infertility affects approximately 15% of reproductive-aged couples worldwide, of which up to 30% of the cases are caused by male factors alone. The origin of male infertility is mostly attributed to sperm abnormalities, of which many are caused by genetic defects. The development of intracytoplasmic sperm injection (ICSI) has helped to circumvent most male infertility conditions. However, there is still a challenging group of infertile males whose sperm, although having normal sperm parameters, are unable to activate the oocyte, even after ICSI treatment. While ICSI generally allows fertilization rates of 70 to 80%, total fertilization failure (FF) still occurs in 1 to 3% of ICSI cycles. Phospholipase C zeta (PLCζ) has been demonstrated to be a critical sperm oocyte activating factor (SOAF) and the absence, reduced, or altered forms of PLCζ have been shown to cause male infertility-related FF. The purpose of this review is to (i) summarize the current knowledge on PLCζ as the critical sperm factor for successful fertilization, as well as to discuss the existence of alternative sperm-induced oocyte activation mechanisms, (ii) describe the diagnostic tests available to determine the cause of FF, and (iii) summarize the beneficial effect of assisted oocyte activation (AOA) to overcome FF.

Reactive oxygen species in reproduction: harmful, essential or both?

The process of embryonic development is crucial and radically influences preimplantation embryo competence. It involves oocyte maturation, fertilization, cell division and blastulation and is characterized by different key phases that have major influences on embryo quality. Each stage of the process of preimplantation embryonic development is led by important signalling pathways that include very many regulatory molecules, such as primary and secondary messengers. Many studies, both in vivo and in vitro, have shown the importance of the contribution of reactive oxygen species (ROS) as important second messengers in embryo development. ROS may originate from embryo metabolism and/or oocyte/embryo surroundings, and their effect on embryonic development is highly variable, depending on the needs of the embryo at each stage of development and on their environment (in vivo or under in vitro culture conditions). Other studies have also shown the deleterious effects of ROS in embryo development, when cellular tissue production overwhelms antioxidant production, leading to oxidative stress. This stress is known to be the cause of many cellular alterations, such as protein, lipid, and DNA damage. Considering that the same ROS level can have a deleterious effect on the fertilizing oocyte or embryo at certain stages, and a positive effect at another stage of the development process, further studies need to be carried out to determine the rate of ROS that benefits the embryo and from what rate it starts to be harmful, this measured at each key phase of embryonic development.

Cellular and molecular aspects of oocyte maturation and fertilization: a perspective from the actin cytoskeleton

ABSTRACT

Much of the scientific knowledge on oocyte maturation, fertilization, and embryonic development has come from the experiments using gametes of marine organisms that reproduce by external fertilization. In particular, echinoderm eggs have enabled the study of structural and biochemical changes related to meiotic maturation and fertilization owing to the abundant availability of large and transparent oocytes and eggs. Thus, in vitro studies of oocyte maturation and sperm-induced egg activation in starfish are carried out under experimental conditions that resemble those occurring in nature. During the maturation process, immature oocytes of starfish are released from the prophase of the first meiotic division, and acquire the competence to be fertilized through a highly programmed sequence of morphological and physiological changes at the oocyte surface. In addition, the changes in the cortical and nuclear regions are essential for normal and monospermic fertilization. This review summarizes the current state of research on the cortical actin cytoskeleton in mediating structural and physiological changes during oocyte maturation and sperm and egg activation in starfish and sea urchin. The common denominator in these studies with echinoderms is that exquisite rearrangements of the egg cortical actin filaments play pivotal roles in gamete interactions, Ca2+ signaling, exocytosis of cortical granules, and control of monospermic fertilization. In this review, we also compare findings from studies using invertebrate eggs with what is known about the contributions made by the actin cytoskeleton in mammalian eggs. Since the cortical actin cytoskeleton affects microvillar morphology, movement, and positioning of organelles and vesicles, and the topography of the egg surface, these changes have impacts on the fertilization process, as has been suggested by recent morphological studies on starfish oocytes and eggs using scanning electron microscopy. Drawing the parallelism between vitelline layer of echinoderm eggs and the zona pellucida of mammalian eggs, we also discuss the importance of the egg surface in mediating monospermic fertilization.

GRAPHICAL ABSTRACT

Influence of oocyte selection, activation with a zinc chelator and inhibition of histone deacetylases on cloned porcine embryo and chemically activated oocytes development

The aim of this study was to evaluate the effects of alternative protocols to improve oocyte selection, embryo activation and genomic reprogramming on in vitro development of porcine embryos cloned by somatic cell nuclear transfer (SCNT). In Experiment 1, in vitro-matured oocytes were selected by exposure to a hyperosmotic sucrose solution prior to micromanipulation. In Experiment 2, an alternative chemical activation protocol using a zinc chelator as an adjuvant (ionomycin + N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) + N-6-dimethylaminopurine (6-DMAP)) was compared with a standard protocol (ionomycin + 6-DMAP) for the activation of porcine oocytes or SCNT embryos. In Experiment 3, presumptive cloned zygotes were incubated after chemical activation in a histone deacetylase inhibitor (Scriptaid) for 15 h, with the evaluation of embryo yield and total cell number in day 7 blastocysts. In Experiment 1, cleavage rates tended to be higher in sucrose-treated oocytes than controls (123/199, 61.8% vs. 119/222, 53.6%, respectively); however, blastocyst rates were similar between groups. In Experiment 2, cleavage rates were higher in zygotes treated with TPEN than controls but no difference in blastocyst rates between groups occurred. For Experiment 3, the exposure to Scriptaid did not improve embryo development after cloning. Nevertheless, the total number of cells was higher in cloned zygotes treated with Scriptaid than SCNT controls. In conclusion, oocyte selection by sucrose as well as treatments with zinc chelator and an inhibitor of histone deacetylases did not significantly improve blastocyst yield in cloned and parthenotes. However, the histone deacetylases inhibitor produced a significant improvement in the blastocyst quality.

Increasing associations between defects in phospholipase C zeta and conditions of male infertility: not just ICSI failure?

PURPOSE

Oocyte activation is a fundamental event at mammalian fertilization. In mammals, this process is initiated by a series of characteristic calcium (Ca²⁺) oscillations, induced by a sperm-specific phospholipase C (PLC) termed PLCzeta (PLCζ). Dysfunction/reduction/deletion of PLCζ is associated with forms of male infertility where the sperm is unable to initiate Ca²⁺ oscillations and oocyte activation, specifically in cases of fertilization failure. This review article aims to systematically summarize recent advancements and controversies in the field to update expanding clinical associations between PLCζ and various male factor conditions. This article also discusses how such associations may potentially underlie defective embryogenesis and recurrent implantation failure following fertility treatments, alongside potential diagnostic and therapeutic PLCζ approaches, aiming to direct future research efforts to utilize such knowledge clinically.

METHODS

An extensive literature search was performed using literature databases (PubMed/MEDLINE/Web of Knowledge) focusing on phospholipase C zeta (PLCzeta; PLCζ), oocyte activation, and calcium oscillations, as well as specific male factor conditions.

RESULTS AND DISCUSSION

Defective PLCζ or PLCζ-induced Ca²⁺ release can be linked to multiple forms of male infertility including abnormal sperm parameters and morphology, sperm DNA fragmentation and oxidation, and abnormal embryogenesis/pregnancies. Such sperm exhibit absent/reduced levels, and abnormal localization patterns of PLCζ within the sperm head.

CONCLUSIONS

Defective PLCζ and abnormal patterns of Ca²⁺ release are increasingly suspected a significant causative factor underlying abnormalities or insufficiencies in Ca²⁺ oscillation-driven early embryogenic events. Such cases could potentially strongly benefit from relevant therapeutic and diagnostic applications of PLCζ, or even alternative mechanisms, following further focused research efforts.

Toward the understanding of biology of oocyte life cycle in Xenopus Laevis: No oocytes left behind

BACKGROUND

For the past more than 25 years, we have been focusing on the developmental and reproductive biology of the female gametes, oocytes, and eggs, of the African clawed frog Xenopus laevis.

METHODS

The events associated with the life cycle of these cells can be classified into the four main categories: first, oogenesis and cell growth in the ovary during the first meiotic arrest; second, maturation and ovulation that occur simultaneously and result in the acquisition of fertilization competence and the second meiotic arrest; third, fertilization, that is sperm-induced transition from egg to zygote; and fourth, egg death after spontaneous activation in the absence of fertilizing sperm.

MAIN FINDINGS

Our studies have demonstrated that signal transduction system involving tyrosine kinase Src and other oocyte/egg membrane-associated molecules such as uroplakin III and some other cytoplasmic proteins such as mitogen-activated protein kinase (MAPK) play important roles for successful ovulation, maturation, fertilization, and initiation of embryonic development.

CONCLUSION

We summarize recent advances in understanding cellular and molecular mechanisms underlying life cycle events of the oocytes and eggs. Our further intention is to discuss and predict potentially promising impact of the recent findings on the challenges facing reproductive biology and medicine, as well as societal contexts.

Endoplasmic reticulum distribution during bovine oocyte activation is regulated by protein kinase C via actin filaments

Fertilization-induced [Ca²⁺ ]_i oscillations generally depend on the release of calcium ions from the endoplasmic reticulum (ER). Since ER is the main store of calcium ions, it plays an important role in oocyte fertilization. However, the mechanism of ER organization at oocyte activation is unknown. Here, we show that protein kinase C (PKC) is involved in ER distribution during bovine oocyte activation, but not involved in cell cycle resumption and spindle organization. Actin filaments were affected by PKC pharmacological inhibition. In addition, similar to PKC results, the actin-depolymerizing drug cytochalasin B affected the ER distribution during oocyte activation. Specifically, we have demonstrated that ER organization during bovine oocyte activation is regulated by PKC possibly through its action on actin filaments regulation. Taken together, the results presented here provide further information on the pathway involved in the regulation of ER organization during oocyte activation and new insight into the functional role of PKC and actin filaments during this process.

High Dosages of Equine Chorionic Gonadotropin Exert Adverse Effects on the Developmental Competence of IVF-Derived Mouse Embryos and Cause Oxidative Stress-Induced Aneuploidy

Gonadotropins play vital roles in the regulation of female reproductive ability and fertility. Our study aimed to determine the effects of superovulation induced by increasing doses of equine chorionic gonadotropin [eCG; also referred to as pregnant mare serum gonadotropin (PMSG)] on the developmental competence of mouse embryos and on aneuploidy formation during in vitro fertilization (IVF). eCG dose-dependently enhanced the oocyte yield from each mouse. Administration of 15 IU eCG significantly reduced the fertilization rate and the formation of four-cell embryos and blastocysts and increased the risk of chromosome aneuploidy. The IVF-derived blastocysts in the 15 IU eCG treatment group had the fewest total cells, inner cell mass (ICM) cells and trophectoderm (TE) cells. Moreover, more blastocysts and fewer apoptotic cells were observed in the 0, 5, and 10 IU eCG treatment groups than in the 15 IU eCG treatment group. We also investigated reactive oxygen species (ROS) levels and variations in several variables: mitochondrial membrane potential (MMP); active mitochondria; mitochondrial superoxide production; adenosine triphosphate (ATP) content; spindle structures; chromosome karyotypes; microfilament distribution; and the expression of Aurora B [an important component of the chromosomal passenger complex (CPC)], the spindle assembly checkpoint (SAC) protein mitotic arrest deficient 2 like 1 (MAD2L1), and the DNA damage response (DDR) protein γH2AX. Injection of 15 IU eCG increased ROS levels, rapidly reduced MMP, increased active mitochondria numbers and mitochondrial superoxide production, reduced ATP content, increased abnormal spindle formation rates, and induced abnormalities in chromosome number and microfilament distribution, suggesting that a high dose of eCG might alter developmental competence and exert negative effects on IVF-obtained mouse embryos. Additionally, the appearance of γH2AX and the significantly increased expression of Aurora B and MAD2L1 suggested that administration of relatively high doses of eCG caused Aurora B-mediated SAC activation triggered by ROS-induced DNA damage in early mouse IVF-derived embryos for self-correction of aneuploidy formation. These findings improve our understanding of the application of gonadotropins and provide a theoretical basis for gonadotropin treatment.

Ca2+ Signaling and Homeostasis in Mammalian Oocytes and Eggs

Changes in the intracellular concentration of calcium ([Ca2+]i) represent a vital signaling mechanism enabling communication between and among cells as well as with the environment. Cells have developed a sophisticated set of molecules, "the Ca2+ toolkit," to adapt [Ca2+]i changes to specific cellular functions. Mammalian oocytes and eggs, the subject of this review, are not an exception, and in fact the initiation of embryo devolvement in all species is entirely dependent on distinct [Ca2+]i responses. Here, we review the components of the Ca2+ toolkit present in mammalian oocytes and eggs, the regulatory mechanisms that allow these cells to accumulate Ca2+ in the endoplasmic reticulum, release it, and maintain basal and stable cytoplasmic concentrations. We also discuss electrophysiological and genetic studies that have uncovered Ca2+ influx channels in oocytes and eggs, and we analyze evidence supporting the role of a sperm-specific phospholipase C isoform as the trigger of Ca2+ oscillations during mammalian fertilization including its implication in fertility.

PKCδ promotes fertilization of mouse embryos in early development via the Cdc25B signaling pathway

Protein kinase C type δ (PKCδ) is involved in B-cell signaling and the regulation of growth, apoptosis and differentiation of a variety of cell types. Cell division cycle 25 (Cdc25) is a key mediator of cell cycle progression that activates cyclin-dependent kinase complexes that drive the cell cycle and participates in the regulation of DNA damage checkpoints. Cdc25B is a member of the Cdc25 family of phosphatases. The present study investigated the role and mechanism of PKCδ in regulating the fertilization of mouse embryos in early development. The expression and subcellular localization of PKCδ and Cdc25B were detected using reverse transcription-quantitative polymerase chain reaction, western blotting and immunofluorescence in one-cell stage mouse embryos. Specific small interfering RNAs targeting PKCδ were used to knockdown the expression of PKCδ. Subsequently, Scansite software was used to predict the target of phosphorylated Cdc25B. Western blotting was used to measure the effects of phosphorylation and dephosphorylation in one-cell stage mouse embryos at different cell cycle phases. PKCδ was expressed during M phase and served a positive role in one-cell stage mouse embryos. Immunofluorescence data revealed that PKCδ and Cdc25B were expressed during G₁, S, G₂ and M phases of the cell cycle. Furthermore, phosphorylated levels of Cdc25B-Ser96 were observed during G₂ and M phases. Microinjection with mimics of phosphorylated Cdc25B-Ser96 mRNA promoted the development of one-cell stage mouse embryos. When PKCδ was suppressed, microinjection with mimics of phosphorylated Cdc25B-Ser96 mRNA reversed the inhibition of PKCδ. To conclude, PKCδ serves a positive role in the first cell cycle of mouse embryos by phosphorylating Cdc25B-Ser96, and provides novel insights for the regulation of early embryonic development.

Human oocyte calcium analysis predicts the response to assisted oocyte activation in patients experiencing fertilization failure after ICSI

STUDY QUESTION

Can human oocyte calcium analysis predict fertilization success after assisted oocyte activation (AOA) in patients experiencing fertilization failure after ICSI?

SUMMARY ANSWER

ICSI-AOA restores the fertilization rate only in patients displaying abnormal Ca2+ oscillations during human oocyte activation.

WHAT IS KNOWN ALREADY

Patients capable of activating mouse oocytes and who showed abnormal Ca2+ profiles after mouse oocyte Ca2+ analysis (M-OCA), have variable responses to ICSI-AOA. It remains unsettled whether human oocyte Ca2+ analysis (H-OCA) would yield an improved accuracy to predict fertilization success after ICSI-AOA.

STUDY DESIGN, SIZE, DURATION

Sperm activation potential was first evaluated by MOAT. Subsequently, Ca2+ oscillatory patterns were determined with sperm from patients showing moderate to normal activation potential based on the capacity of human sperm to generate Ca2+ responses upon microinjection in mouse and human oocytes. Altogether, this study includes a total of 255 mouse and 122 human oocytes. M-OCA was performed with 16 different sperm samples before undergoing ICSI-AOA treatment. H-OCA was performed for 11 patients who finally underwent ICSI-AOA treatment. The diagnostic accuracy to predict fertilization success was calculated based on the response to ICSI-AOA.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients experiencing low or total failed fertilization after conventional ICSI were included in the study. All participants showed moderate to high rates of activation after MOAT. Metaphase II (MII) oocytes from B6D2F1 mice were used for M-OCA. Control fertile sperm samples were used to obtain a reference Ca2+ oscillation profile elicited in human oocytes. Donated human oocytes, non-suitable for IVF treatments, were collected and vitrified at MII stage for further analysis by H-OCA.

MAIN RESULTS AND THE ROLE OF CHANCE

M-OCA and H-OCA predicted the response to ICSI-AOA in 8 out of 11 (73%) patients. Compared to M-OCA, H-OCA detected the presence of sperm activation deficiencies with greater sensitivity (75 vs 100%, respectively). ICSI-AOA never showed benefit to overcome fertilization failure in patients showing normal capacity to generate Ca2+ oscillations in H-OCA and was likely to be beneficial in cases displaying abnormal H-OCA Ca2+ oscillations patterns.

LIMITATIONS, REASONS FOR CAUTION

The scarce availability of human oocytes donated for research purposes is a limiting factor to perform H-OCA. Ca2+ imaging requires specific equipment to monitor fluorescence changes over time.

WIDER IMPLICATIONS OF THE FINDINGS

H-OCA is a sensitive test to diagnose gamete-linked fertilization failure. H-OCA allows treatment counseling for couples experiencing ICSI failures to either undergo ICSI-AOA or to participate in gamete donation programs. The present data provide an important template of the Ca2+ signature observed during human fertilization in cases with normal, low and failed fertilization after conventional ICSI.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Flemish fund for scientific research (FWO-Vlaanderen, G060615N). The authors have no conflict of interest to declare.

Advances in the study of egg activation of higher plants

Fertilization in higher plants induces many structural and physiological changes in the fertilized egg, and represents the transition from the haploid female gamete to the diploid zygote, the first cell of a sporophyte. Some changes are induced extremely rapidly following fusion with sperm cells and are the preclusions of egg activation. This review focuses on the early changes that occur in the egg after fusion with sperm cells, but before nuclear fusion. Reported changes include cell shrinkage, cell wall formation, polarity change, oscillation in Ca2+ concentration, and DNA synthesis. In addition, the current understanding of egg activation is summarized and the possible functional relevance of the changes is explored.

OTA induces intestinal epithelial barrier dysfunction and tight junction disruption in IPEC-J2 cells through ROS/Ca2+-mediated MLCK activation

Ochratoxin A (OTA) is a frequent contaminant of feed and food worldwide. The toxicity of OTA on intestinal barrier was investigated in porcine intestinal epithelial cells (IPEC-J2). We observed that OTA induced intestinal barrier dysfunction as indicated by the reduction in transepithelial electrical resistance (TEER) and elevation in paracellular permeability to 4 kDa dextran. The barrier dysfunction was accompanied with tight junction disruption including a down-regulation in ZO-1 expression and redistribution of Occludin and ZO-1. Moreover, OTA exposure increased reactive oxygen species (ROS) generation, elevated the intracellular calcium level ([Ca²⁺]_c) and activated myosin light chain kinase (MLCK). Simultaneously, NAC, a ROS scavenger, blocked OTA-induced ROS generation, [Ca²⁺]_c elevation, barrier dysfunction and tight junction disruption, suggesting that OTA-induced ROS generation may act as a trigger. Next, we found that OTA-induced MLCK activation was inhibited by BAPTA-AM, the cytosolic Ca²⁺ chelator, demonstrating that OTA-induced MLCK activation is dependent on [Ca²⁺]_c elevation. Furthermore, inhibition of MLCK with ML-7 or inhibition of [Ca²⁺]_c elevation with BAPTA-AM markedly prevented OTA-induced barrier dysfunction and tight junction disruption. Taken together, our results indicated that OTA induces ROS generation, and then elevates the [Ca²⁺]_c and MLCK activity in turn, which finally induces barrier dysfunction and disrupts tight junction in IPEC-J2 cell monolayers.

Non-centrosomal microtubule structures regulated by egg activation signaling contribute to cytoplasmic and cortical reorganization in the ascidian egg

In the first ascidian cell cycle, cytoplasmic and cortical reorganization is required for distributing maternal factors to their appropriate positions, resulting in the formation of the embryonic axis. This cytoplasmic reorganization is considered to depend on the cortical microfilament network in the first phase and on the sperm astral microtubule (MT) in the second phase. Recently, we described three novel MT structures: a deeply extended MT meshwork (DEM) in the entire subcortical region of the unfertilized egg, transiently accumulated MT fragments (TAF) in the vegetal pole, and a cortical MT array in the posterior vegetal cortex (CAMP). Particularly, our previous study showed CAMP to contribute to the movement of myoplasm. In addition, it is very similar to the parallel MT array, which appears during cortical rotation in Xenopus eggs. However, how these MT structures are organized is still unclear. Here, we investigated the relationship between the egg activation pathway and MT structures during the first ascidian cell cycle. First, we carefully analyzed cell cycle progression through meiosis I and II and the first mitosis, and successfully established a standard time table of cell cycle events. Using this time table as a reference, we precisely described the behavior of novel MT structures and revealed that it was closely correlated with cell cycle events. Moreover, pharmacological experiments supported the relationship between these MT structures and the signal transduction mechanisms that begin after fertilization, including Ca²⁺ signaling, MPF signaling, and MEK/MAPK signaling. Especially, CAMP formation was directed by activities of cyclin-dependent kinases. As these MT structures are conserved, at least, within chordate group, we emphasize the importance of understanding the controlling mechanisms of MT dynamics, which is important for embryonic axis determination in the ascidian egg.

Ca2+ -depended signaling pathways regulate self-renewal and pluripotency of stem cells

Ca²⁺ -mediated signaling is widely spread in nature and plays critical role in the individual development of various organisms ranging from microorganisms to mammals. In vertebrates, Ca²⁺ is involved in important developmental events: fertilization, body plan establishment, and organogenesis. The two later events are defined by embryonic stem cells (ESCs). ESCs are capable of self-renewal and are pluripotent by nature, that is, can give rise to all types of cells that make up the body. Given the paramount importance of Ca²⁺ signalization in the development, it is therefore not surprising this process also plays role in the biology of stem cells. In this review, we scrutinize the published experimental data on the role of Ca²⁺ ions in embryonic stem cells self-renewal and pluripotency. In line with this, we also discuss possible mechanisms of p53 inhibition as a major hindrance to self-renewal of ESCs. Finally, we argue about the role of G-protein-coupled receptors (GPCRs), the largest family of heteromeric transmembrane receptors, and GPCR-mediated signalization in stem cells, and propose the role for the GPCR-G-protein-PLC-Ca²⁺ -downstream signaling pathway in the regulation of pluripotency of both mouse and human ESCs.