Search Results (121)

Background/Objectives: Early embryonic arrest during the cleavage stage (days 2–4) accounts for a substantial proportion of developmental failure in in vitro fertilization. This phenomenon remains poorly understood at the molecular level, even in chromosomally normal embryos identified by preimplantation genetic testing. This review aims to redefine cleavage-stage arrest from a passive energy deficit to a checkpoint-regulated endpoint caused by inadequate coordination among metabolism, transcriptome integrity, and stress-response pathways. Methods: We integrate evidence from long-read transcriptomics, metabolomics, epigenetics, and immunobiology relevant to pre-blastocyst development. These data are assembled into a unifying mechanistic framework and a clinically oriented stratification model, together with candidate multimodal readouts for early classification. Results: We propose a three-axis model linking: (i) metabolic–epigenetic insufficiency, including defective histone lactylation and impaired alpha-ketoglutarate-dependent DNA demethylation; (ii) isoform-level abnormalities, including intron retention and retrotransposon activation within a hidden transcriptomic landscape better resolved by long-read sequencing; and (iii) stress-related immune signaling, in which NLRP7 links alternative splicing and DNA-damage-response dysfunction with mitochondrial stress and p53-associated arrest. Within this framework, we distinguish three molecular arrest states: an early transition failure marked by defective maternal-to-embryonic reprogramming and severe splicing disruption; a metabolically quiescent state that may retain a limited rescue window; and a later stress-associated state characterized by senescence-like features, oxidative stress, and broad transcriptomic and genomic instability. Conclusions: Early embryo arrest should no longer be viewed as a nonspecific developmental failure, but as a mechanistically stratifiable condition with distinct metabolic, transcriptomic, and stress-associated trajectories. A diagnostic platform combining fluorescence lifetime imaging microscopy, long-read sequencing, and digital polymerase chain reaction may improve early mechanistic classification, help identify embryos with possible reversibility, and reduce uncertainty in embryo selection during in vitro fertilization. Full article

Papaya (Carica papaya L.) is a highly cross-pollinated crop that exhibits considerable genetic variability when propagated through seeds, resulting in non-true-to-type progeny. Therefore, the development of an efficient in vitro regeneration system is essential for large-scale clonal propagation of elite cultivars. In the present study, a highly efficient and reproducible somatic embryogenesis protocol was developed for C. papaya var. TNAU Papaya CO 8 using immature zygotic embryos as explants. This study provides the first comprehensive comparative evaluation of three basal media, viz., Murashige and Skoog Medium, N6 Medium, and Woody Plant Medium, for somatic embryogenesis and plant regeneration in this variety, along with the optimization of polyamine-enriched media for enhanced plantlet recovery. The embryogenic potential of explants was assessed across different stages, including callus induction, somatic embryo development, plant regeneration, shoot elongation, rooting, and acclimatization. Maximum callus induction (81.96%) was observed on half-strength MS medium supplemented with 2,4-Dichlorophenoxyacetic acid under dark conditions, followed by ½ N6 (63.00%) and ½ WPM (58.02%). Somatic embryo initiation was highest on ½ MS medium containing 2.0 mgL⁻¹ 2,4-D (77.82%). Somatic embryos developed through distinct globular, heart, torpedo, and cotyledonary stages. Embryo maturation was significantly enhanced on MS medium supplemented with abscisic acid, polyethylene glycol, benzylaminopurine, and proline. The highest plantlet regeneration (85.02%) was achieved on MS medium enriched with putrescine, whereas comparatively lower regeneration was recorded on N6 (75.99%) and WPM (57.97%). Shoot elongation was significantly improved by supplementation with gibberellic acid (1.0 mgL⁻¹). Root induction was optimal on half-strength MS medium containing Indole-3-butyric acid, 1-Naphthaleneacetic acid, phloroglucinol, and activated charcoal, resulting in well-developed roots. Regenerated plantlets were successfully acclimatized in a cocopeat–vermicompost substrate with a survival rate of 74.01%. The optimized protocol provides a reliable and efficient system for large-scale clonal propagation and offers promising applications in genetic transformation and commercial production of papaya var. TNAU papaya CO 8. Full article

Female reproductive aging is associated with a progressive decline in oocyte competence and reduced success in assisted reproductive technologies. While chromosomal abnormalities, mitochondrial dysfunction, and DNA damage have been extensively studied, these mechanisms do not fully explain developmental arrest in chromosomally euploid embryos or the variability in embryo competence. Human oocytes enter a transcriptionally quiescent state during meiotic maturation and rely almost entirely on the regulated translation of stored maternal messenger RNAs to support fertilization and early embryonic development until zygotic genome activation. In this context, translational fidelity becomes a critical determinant of proteome integrity and cellular function. Age-related alterations affecting ribosomal RNA integrity, transfer RNA modification, aminoacylation accuracy, and translational regulatory networks may impair the precision, timing, and coordination of protein synthesis. These defects can disrupt essential processes such as spindle assembly, cytoskeletal organization, and early cleavage dynamics, ultimately compromising embryo viability despite chromosomal normality. In addition, the follicular microenvironment, including redox balance, metabolic support, and signaling pathways, plays a crucial upstream role in maintaining translational integrity. This review integrates mechanistic evidence from molecular, cellular, and developmental studies to propose that progressive decline in translational fidelity represents a fundamental and previously underrecognized driver of reproductive aging. Understanding translational control as a central regulator of oocyte competence may provide new insights into unexplained IVF failure and support the development of novel biomarkers and therapeutic strategies aimed at preserving reproductive potential. Full article

Human preimplantation embryo arrest (PREMBA) represents a significant clinical hurdle in assisted reproductive technology (ART), in which approximately 10% of in vitro fertilized (IVF) embryos arrest at the cleavage stages. Whole-exome sequencing (WES) studies have discovered numerous genetic mutations associated with preimplantation embryo arrest. These mutations often disrupt critical biological milestones such as maternal mRNA clearance (BTG4, ZFP36L2, ZAR1), subcortical maternal complex (TLE6, PADI6, OOEP, NLRP2, NLRP5, NLRP7, KHDC3L), DNA double-strand break formation and homologous recombination (REC114, TOP6BL, MEI1, MEI4, TRIP13), spindle assembly (TUBB8 and TUBA4A) and cell cycle and checkpoints (FBXO43, MOS, CHEK1, TRIP13, CDC20), as well as nuclear transport and translational regulation (KPNA7, DDOST). However, the cause of most clinical cases remains genetically unexplained. Studies investigating these unexplained arrests have uncovered widespread multi-omics abnormalities, including transcriptional arrest, DNA hypermethylation, higher chromatin accessibility, aberrant histone modification, chromosomal aneuploidy and senescent-like states. This review provides a comprehensive overview of the molecular mechanisms underlying PREMBA, categorized into those that are attributable to known genetic mutations and those with unexplained reasons. Full article

The proper regulation of signaling pathways, including WNT signaling, during early embryonic development is critical for whole-organism development. In particular, maternally enriched WNTs play critical roles in cell cleavage and axis formation through non-canonical and canonical pathways during early embryogenesis. However, early developmental processes related to maternal WNTs and their underlying mechanisms have remained unstudied in avian species. In this study, we investigated WNT signaling-mediated early development in the chicken embryo. We found that WNT4 and WNT6, different ligands from other species, exhibited expression patterns consistent with maternal enrichment in chicken. The chemical inhibition of maternal WNT signaling in intrauterine embryos led to aberrant zygotic expression of WNT8C, which is important for primitive streak formation. Combined with in vitro functional studies, we demonstrated that WNT4 increased WNT8C expression through the non-canonical JNK pathway and that WNT8C subsequently promoted the canonical β-catenin pathway. Our results indicate that maternal WNT4 activates zygotic WNT8C and potentially regulates embryonic polarity in chicken. Full article

The rhesus macaque is one of the closest evolutionary relatives to humans, making the study of alternative splicing (AS) during its early embryonic development highly valuable for understanding human embryogenesis and related diseases. However, systematic studies in this context remain limited. Here, a comprehensive bioinformatic analysis of AS was performed using RNA-seq data spanning early rhesus macaque embryogenesis. We identified multiple previously unannotated zygotic genome activation (ZGA) genes, thereby refining the rhesus macaque ZGA gene repertoire. The landscape of AS and differential AS events (DASEs) across early stages was characterized, revealing dynamic and stage-specific regulation, with a marked increase in AS events from the 8-cell to morula stages. In addition, weighted gene co-expression network analysis identified 35 key splicing factors (SFs) involved in regulating early rhesus macaque embryonic development. Finally, we calculated the correlation between differentially expressed SFs and DASEs during the ZGA process, and identified potential regulatory relationships between several SFs (TRA2B, IGF2BP1, HNRNPAB, and MATR3) and specific DASEs. Collectively, this study provides the first systematic analysis of AS dynamics and regulation in early rhesus macaque embryogenesis, highlighting its critical role in development and offering a valuable reference for understanding AS in early human embryos. Full article

Background/Objectives: Current genomics research equates the genome with DNA sequence and treats the epigenome as a regulatory layer. This DNA-centric view obscures the fact that genomic identity arises through epigenomic processes. The objective of this article is to reinterpret published findings into a new theoretical framework: the EpG² (Epigenome–Genome) system. Methods: This work develops a new conceptual framework by integrating published evidence from diverse domains—including enhancer biology, overlapping genomic functions, alternative coding frames, zygotic genome activation, and disease-associated loci—and reinterpreting these findings through the lens of epigenomic processes. Results: Evidence shows that enhancers emerge only through the interplay of sequence, transcription factors, and chromatin environment. At fertilization, paternal and maternal genomes remain separate, and a new genome emerges through coordinated epigenomic reprogramming or zygote genome emergence (ZGE). DNA sequence risk variants illustrate the concept of contextual risk alleles, whose effects shift across tissues and developmental stages as epigenomic contexts change. Conclusions: The EpG² system reframes the genome as a processual, emergent entity generated and regulated by epigenomic processes, offering a paradigm for understanding genomic variation beyond DNA sequence. Full article

The maternal-to-zygotic transition (MZT) is a fundamental process in vertebrate embryogenesis, involving the clearance of maternal mRNA and activation of the zygotic genome. Orchestration of maternal mRNA stability ensures early embryogenesis. Recently, some germ plasm (GP) factors have been demonstrated to regulate the stability of maternal mRNA. Bucky ball (Buc) functions as a zebrafish GP organizer. However, it remains unclear whether Buc also protects maternal mRNAs from widespread decay in early embryos. Here, we report that overexpression of buc results in delayed maternal mRNA degradation and a concomitant delay in embryonic development, whereas buc knockout leads to accelerated maternal mRNA degradation and severe developmental defects, suggesting that both gain and loss of buc perturb early developmental programs. Mechanistically, this regulatory mechanism of Buc on maternal mRNA is mediated through the expression of RNA-binding protein Igf2bp3. Together, our findings suggest that the GP organizer Buc may stabilize maternal mRNAs in coordination with Igf2bp3, thereby contributing to the maintenance of maternal mRNA required for proper embryonic development during the MZT. This study expands the functional scope of Buc beyond GP assembly and reveals its critical role in safeguarding maternal mRNA integrity to ensure proper embryo development. Full article

Gynogenesis is a reproductive mode where offspring inherit exclusively maternal chromosomes. Gynogenetic development in fish may be induced intentionally by activating eggs with the UV-irradiated, inactive spermatozoa. In the meiotic variant of gynogenesis, the resultant haploid gynogenetic zygote is then exposed to a physical shock to inhibit the release of the 2nd polar body and to reconstitute the diploid state of the embryo. Here, meiotic gynogenesis was induced in the rainbow trout eggs from different clutches to find any differences in terms of gene expression and antioxidant enzyme activity between eggs with high and low ability for gynogenetic development. The survival rates of the gynogenotes after hatching from the eggs originating from five females varied from 16.6 ± 4.3% to 53.8 ± 9.8%. Biochemical and molecular examination revealed that eggs with higher developmental potential for meiotic gynogenesis exhibited significantly greater glutathione peroxidase (GPx) activity than eggs with lower efficiency of gynogenesis. Moreover, eggs exhibiting the highest ability for gynogenetic development showed increased transcription of the keratin 8 gene and decreased abundance of keratin 18 and tubulin β mRNA transcripts. Since keratins protect oocytes from physical stress after ovulation, the high abundance of keratin 8 in the rainbow trout eggs may increase their resilience to the physical shock applied for the zygote diploidization during gynogenesis. On the other hand, a low level of tubulin-building microtubules may increase the efficiency of high hydrostatic pressure (HHP) shock used for diploidization of the gynogenetic zygotes. Full article

In vitro fertilization (IVF) exposes embryos to environmental stressors that can disrupt early development and confer long-term health risks, though the mechanisms remain poorly understood. Here, we tested the hypothesis that reducing incubation temperature during the first zygotic cleavage would promote long-term developmental stability in IVF-conceived offspring. Using a mouse model, we compared the long-term effects of standard (37 °C) versus reduced (35 °C) IVF culture temperature on energy balance, circadian rhythms, sleep architecture, and brain histone modifications. Although offspring from both IVF groups exhibited increased body mass without notable effects on glucose metabolism, significant disruptions in circadian rhythms and sleep–wake patterns were detected. The 37 °C group exhibited altered amplitudes in oxygen consumption rhythms and respiratory exchange ratios, as well as pronounced alterations in sleep–wake patterns, including reduced sleep duration and increased nighttime activity. The 35 °C group displayed intermediate phenotypes, substantiating the importance of optimizing embryo incubation parameters. These metabolic and behavioral changes were paralleled by altered histone modifications in the cerebral cortex of IVF offspring, suggesting an epigenetic basis for circadian misalignment. Our results identify disrupted circadian rhythm and sleep architecture as a novel mechanism contributing to metabolic dysfunction in IVF-conceived offspring. The partial mitigation of these effects through reduced culture temperature underscores the importance of optimizing IVF protocols to minimize long-term epigenetic and metabolic risks. Full article

Grain amaranths are recalcitrant to conventional in vitro plant regeneration by organogenesis de novo or through somatic embryogenesis. Consequently, floral organogenesis by these methods, representing the culminating developmental point in angiosperms, is rarely achieved. In the present study, the manipulation of in vitro flowering was explored as part of a strategy designed to overcome grain amaranth’s regeneration recalcitrance. It led to an efficient and reproducible in vitro protocol in which half-longitudinally dissected zygotic embryos generated fully developed Amaranthus hypochondriacus (Ah) plants. The use of high-irradiance illumination with LED lamps with a 3:1 red–blue irradiance ratio was a critical factor, leading to a 70% rate of early flowering events under flowering-inhibiting long-day photoperiod conditions. Contrariwise, no flowering was induced under LED white lights. All in vitro flowering Ah plants yielded viable seeds. To understand the basic molecular mechanisms of the phenomenon observed, gene expression patterns and principal component analysis of key flowering-related genes were analyzed after cultivation in vitro for 4, 8, and 12 weeks under both lighting regimes. These coded for photoreceptors, photomorphogenetic regulators, embryogenic modulators, and flowering activators/repressors. The results highlighted the upregulation of key flowering-regulatory genes, including CONSTANS, FLOWERING LOCUS T, and LEAFY, together with the downregulation of the floral repressor TERMINAL FLOWER1. Ribosome biogenesis- and seed-development-related genes were also differentially expressed, supporting a key role in this process for protein synthesis and embryogenesis. A model is proposed to explain how this light-regulated molecular framework enables in vitro flowering and seed production in Ah plants kept under long-day photoperiods. Full article

High non-esterified fatty acids (NEFAs) during negative energy balance in dairy cattle can impair reproduction. While their effects on oocyte maturation and preimplantation embryo development are known, their impact during fertilisation is largely unexplored. This study examined the effects of high NEFA exposure exclusively during in vitro fertilisation (IVF). Bovine oocytes were matured in vitro and fertilised under physiological or high NEFA concentrations. High NEFA concentrations decreased fertilisation, cleavage, and blastocyst rates. Reactive oxygen species production in zygotes was not affected, but blastocysts derived from the High-NEFA group had fewer cells. Spermatozoa exposed to high NEFA concentrations exhibited increased plasma membrane and acrosome damage, higher DNA fragmentation, and reduced mitochondrial membrane potential. The expression of H3K27me3, a repressive histone mark normally erased from fertilisation to embryonic genome activation, was higher in 2-cell than in 4-cell embryos on day 2 after IVF, but only in the High-NEFA group. This delayed H3K27me3 loss, along with increased DNA damage, could partially explain the reduced blastocyst formation observed. In conclusion, high NEFA concentrations can impair pre-implantation embryo development during zygote formation, potentially via effects on both the oocyte and spermatozoon. The latter warrants further investigation using an intracytoplasmic sperm injection model. Full article

Zygotic genome activation (ZGA) represents one of the most vulnerable periods to environmental perturbations. The objective of this study was to investigate the formation of stress granules in mouse embryos in response to temperature reduction during ZGA, preimplantation embryo mortality, and long-term phenotypic outcomes. These outcomes included the evaluation of expression noise in bilateral right/left limbs of offspring as an indicator of developmental instability, behavioral deviation, hippocampal volume, and metabolomics profiling in adult offspring. Exposure to hypothermia during ZGA was associated with an increased number and inter-blastomere variability of stress granules, extended duration of the second embryonic division, and elevated embryonic mortality during the second and third cleavage stages. The embryonic response to hypothermic stress correlated with phenotypic traits indicative of increased pathology risk. Expression noise, serving as an indicator of developmental instability, was reduced in adult offspring derived from two-cell embryos incubated at 35 °C compared to those at 37 °C, while showing no significant difference relative to the control group. These results suggest that embryos surviving hypothermic exposure (35 °C) possess enhanced resilience to the adverse effects commonly associated with embryo transfer procedures. Furthermore, increased hippocampal volume and augmented auditory startle reflex observed in offspring that endured hypothermia during ZGA imply reduced risks of cognitive-related pathologies and reduced risks of pathologies associated with cognitive functions. Full article

Grass carp is an economically important cultured species in China. Triploid embryo production is widely applied in aquaculture to achieve reproductive sterility, improve somatic growth, and reduce ecological risks associated with uncontrolled breeding. In this study, a simple cold shock method for inducing triploid grass carp was developed. The triploid induction rate of 71.73 ± 5.00% was achieved by applying a cold treatment at 4 °C for 12 min, starting 2 min after artificial fertilization. Flow cytometry and karyotype analysis revealed that triploid individuals exhibited a 1.5-fold increase in DNA content compared to diploid counterparts, with a chromosomal composition of 3n = 72 (33m + 36sm + 3st). Additionally, embryonic transcriptome analysis demonstrated that, in the cold shock-induced embryos, genes associated with abnormal mesoderm and dorsal–ventral axis formation, zygotic genome activation (ZGA), and anti-apoptosis were downregulated, whereas pro-apoptotic genes were upregulated, which may contribute to the higher abnormal mortality observed during embryonic development. Overall, this study demonstrates optimized conditions for inducing triploidy in grass carp via cold shock and provides insights into the transcriptomic changes that take place in cold shock-induced embryos, which could inform future grass carp genetic breeding programs. Full article

Coconut palm’s economic significance across the tropics, underpinning livelihoods and industries, is increasingly threatened by pests, diseases, genetic erosion, and natural disasters. This underscores the urgent need for efficient germplasm conservation strategies. In vitro culture of zygotic embryos provides a vital pathway for secure global conservation and exchange, particularly for elite varieties like Makapuno. However, standardized, practical protocols for the international exchange of fresh, non-cryopreserved embryos remain underdeveloped. To address this gap, this study refined a key protocol for fresh coconut embryo exchange by systematically optimizing critical parameters. The results demonstrated that an optimal culture medium containing low sucrose (10 g/L), activated charcoal (1 g/L), Gelrite (2.5 g/L), and 1 mL medium per cryotube significantly enhanced embryo size (40% increase; p < 0.05) compared to sucrose-free controls. While surface sterilization using AgNPs showed a marginal growth advantage over NaClO, rigorous transportation simulations confirmed that embryos retain high viability and regeneration potential only if delivered within seven days. These findings establish a robust, standardized framework for enhancing the global exchange and conservation of elite coconut germplasm, directly supporting genetic conservation and varietal improvement efforts. Full article