Reproductive success in dogs and cats remains limited despite advances in assisted reproductive technologies, highlighting the need for a clearer understanding of the ultrastructural processes governing oocyte maturation. This review critically examines current knowledge on the ultrastructural and cytoplasmic mechanisms underlying oocyte maturation in dogs, with particular emphasis on cytoskeletal dynamics, organelle redistribution, mitochondrial activity, and lipid metabolism. Comparative insights from other mammalian species, especially the cat, are integrated to highlight fundamental differences in the timing and regulation of oocyte competence. The evidence suggests that inadequate cytoplasmic maturation, not meiotic progression, is the principal bottleneck affecting fertilization and early embryonic development in dogs. We conclude that future improvements in canine fertility and reproductive technologies will require a shift from predominantly hormonal and nuclear-focused approaches toward strategies targeting oocyte cytoplasmic quality and ultrastructural maturation.

Recurrent implantation failure (RIF), a important contributor to infertility in assisted reproductive technologies, is believed to be primarily to abnormal endometrial decidualization. However, its related molecular mechanisms are still incompletely clear. It has been reported that PANX1 is an ATP-permeable channel to regulate the extracellular ATP, and ATP level could influence the progress of endometrial decidualization. Therefore, we conduct this study to explore the potential role of PANX1 during the development of RIF. In this study, we first compared the the expression of PANX1 in RIF patients and control patients. Then, the human endometrial stromal cells (HESCs) was used to the explore the regulatory function of PANX1 on endometrial decidualization by Immunofluorescence staining, Western blot, RT-PCR, Plasmid transfection and ATP detection. Finally, animal model was established to further confirm the results which were found in vitro. We observed a significant upregulation expression of ATP release channel protein Pannexin1 (PANX1) in endometrial tissue of RIF patients. Moreover, after overexpressing PANX1 in human endometrial stromal cells (HESCs), we found a significantly high concentration of extracellualr ATP (eATP) and the inhibition of HESCs decidualization, which was characterized as the decreasing expression of prolactin (PRL) and insulin-like growth factor binding protein 1 (IGFBP-1), as well as the aberrant morphologic cytoskeletion of HESCs. Surprisingly, knockdown the expression of PANX1 in HESCs also impaired the cellular decidualization, indicating the important role of normal PANX1 expression during the process of endometrial decidualization. The subsequent animal study further confirmed our findings in vitro. The present study clearly showed that abnormal high expression of PANX1 hindered endometrial decidualization through the upregulation of eATP concentrations, ultimately leading to embryo implantation failure. Our findings suggested a novel cause of RIF and identified a potential therapeutic target for RIF.

Male infertility affects approximately 7 to 8% of men worldwide and is influenced by both genetic and epigenetic factors. Epigenetic mechanisms - including DNA methylation, histone modifications, and non-coding RNAs - are essential for spermatogenesis, sperm function, and early embryonic development. Disruptions in these processes can impair fertility and embryo viability. Assisted reproductive technologies (ART), particularly intracytoplasmic sperm injection (ICSI), have enabled conception in previously untreatable cases; however, by bypassing natural selection barriers, they may facilitate the transmission of epigenetic abnormalities. This narrative review summarizes recent clinical and experimental evidence on sperm epigenetics, emphasizing paternal health, sperm epigenetic signatures, and ART-associated developmental risks. During spermatogenesis, extensive epigenetic remodeling occurs, including protamine-histone exchange, selective histone retention, and RNA packaging, all critical for embryogenesis. Conditions such as varicocele, obesity, advanced paternal age, toxin exposure, and malignancy have been linked to abnormal DNA methylation, altered chromatin structure, and dysregulated small RNAs. Seminal extracellular vesicles also mediate environmental influences on implantation and immune modulation. Because ART coincides with windows of epigenetic vulnerability, laboratory procedures - including sperm selection, cryopreservation, and embryo culture - may contribute to imprinting disturbances. Understanding these mechanisms is essential to optimize reproductive safety while preserving ART efficacy.

Progesterone plays a pivotal role in implantation and ongoing pregnancy. In the context of assisted reproductive technology (ART), and in particular frozen embryo transfer (FET), increasing evidence suggests that serum progesterone levels strongly influence reproductive outcomes. This review summarizes the latest findings regarding the optimal range of serum progesterone concentrations and their implications across different endometrial preparation protocols. Observational and interventional studies have consistently shown that suboptimal mid-luteal serum progesterone levels are associated with lower implantation and live birth rates in FET cycles. The need for exogenous supplementation varies according to the type of endometrial preparation, with hormone replacement therapy cycles being particularly sensitive to inadequate progesterone exposure. Emerging data support the concept of individualized luteal support, including serum-guided adjustments or alternative routes of administration in cases of suboptimal serum progesterone levels. Adequate serum progesterone concentrations are critical for optimizing outcomes after FET. Evidence supports a paradigm shift from empirical supplementation to precision medicine approaches based on serum thresholds and patient characteristics. Future research should aim to define universally accepted cutoff values, clarify the role of endometrial versus systemic progesterone, and refine strategies for tailoring luteal phase support in ART.

Sex hormones and arrhythmia risk in women with long-QT syndrome.

Extreme ambient heat and outcomes of assisted reproduction in the continental United States, 1996 to 2018.

Morphokinetic assessment of the blastocyst's trophectoderm re-expansion post-warming: predictive markers for clinical pregnancy in ART.

Long-term metabolic and developmental effects of in vitro embryo technologies in female cattle.

Exposure to endocrine-disrupting chemicals in follicular fluid: implications for assisted reproductive technology outcomes.

Patient motivations and barriers in the donation of surplus embryos: a systematic review.

Fertility after endometriosis surgery: a systematic review and meta-analysis comparison of primary versus multiple surgical interventions.

Women undergoing assisted reproductive technology (ART) often experience depression linked to treatment-related uncertainty. This study examined whether perceived stigma mediates the relationship between uncertainty and depression and whether spousal support moderates this effect. PROCESS Macro Model 14 was used, controlling for miscarriage experience, counseling history, and spousal proactiveness. Conditional indirect effects and the moderated mediation index were assessed using bootstrapping with 95% confidence intervals. Uncertainty significantly predicted perceived stigma (β = 0.56, p < 0.001) and depression (β = 0.54, p = 0.002). Perceived stigma also significantly affected depression (β = 0.61, p < 0.001). However, spousal support (β = -0.09, p = 0.617) and its interaction with stigma (β = 0.02, p = 0.913) were not significant. While indirect effects remained significant at all spousal support levels, the moderated mediation index was nonsignificant (95% CI: -0.15 to 0.21). Perceived stigma mediates the effect of uncertainty on depression, but spousal support does not moderate this pathway. Interventions should target uncertainty and stigma reduction to improve mental health in women undergoing ART.

Paternal preconception urinary concentrations of bisphenol A and F in relation to in vitro fertilization outcomes: A prospective cohort study.

BACKGROUND: Sperm cryopreservation is essential for assisted reproductive technologies, yet current methods face challenges regarding cryoprotectant toxicity and protocol standardization. OBJECTIVE: To develop an optimized cryopreservation system by investigating cryoprotective mechanisms and establishing standardized freezing protocols without using any animal-derived material. MATERIALS AND METHODS: Thermodynamic analysis was performed to evaluate the cryoprotectant efficacy of glycerol (i.e., its ice crystal inhibition properties). An optimized formulation combining 10% glycerol with recombinant human serum albumin (rHSA) was developed to replace traditional egg yolk components. A novel freezing protocol incorporating gradient cooling and precise nucleation at −8.5°C was implemented using a custom-designed automated cryopreservation device (±1°C precision). RESULTS: The optimized formulation significantly reduced the melting enthalpy while it maintained post-thaw sperm motility of 75.4 ± 3.2% and DNA fragmentation index &lt;15%. The freezing protocol achieved 82.6 ± 4.1% recovery rate and reduced ice crystal formation by 62.3%. Preclinical study demonstrated significant improvements versus conventional methods (increased motility by 27.8% and enhanced DNA integrity by 34.6%, both p &lt; 0.01). CONCLUSION: The study established a standardized, pathogen-free cryopreservation system with demonstrated efficacy in preserving sperm quality. The findings provide both technical solutions for clinical practice and fundamental insights into cryoprotective mechanisms.

Downregulation of intracellular ATP levels by PANX1 inhibits ovarian granulosa cell proliferation and mediates follicular dysplasia in elderly women.

The endometrium: is thickness all that counts?

A scoping review on the impact of ambient temperature on human infertility.

CRISPR/Cas9 and reproductive failure: applications, ethical challenges, and future perspectives in human germline genome editing.

Addressing multiple pregnancies in invitro fertilization-embryo transfer: Current status, challenges, and solutions.

The rapid advancement of assisted reproductive technologies has not only expanded the possibilities of human reproduction but also introduced crucial ethical and legal challenges, particularly in the case of posthumous conception. Existing legal frameworks, such as the one-year limit on using cryopreserved sperm in some European countries, often fail to address the emotional and practical needs of surviving partners, exposing significant gaps in current policies. This paper argues that reproductive autonomy should extend beyond death, ensuring that individuals' explicit wishes regarding the use of their gametes or embryos are respected. To bridge this regulatory and ethical gap, we propose the development of reproductive wills, a legal mechanism designed to safeguard postmortem reproductive autonomy. By allowing individuals to specify their reproductive intentions in advance, reproductive wills provide a structured approach to balancing personal autonomy with the rights and interests of surviving partners and potential offspring.