TET enzyme driven epigenetic reprogramming in early embryos and its implication on long-term health

Hif-1α regulation of the Tet1-β-catenin-Dicer1-miRNAs pathway is involved in depression-like behavior in prenatal hypoxic male offspring

Prenatal hypoxia (PH) is a common complication of pregnancy, and it is strongly associated with psychiatric disorders such as depression and anxiety in the offspring. However, how prenatal hypoxia contributes to psychiatric disorders in the offspring is unclear. In this study, we established a model of prenatally hypoxic mice, where pregnant females were treated with hypoxia (10.5% O2) during gestational days 12.5-17.5, while controls (CON) were kept in a normoxic (21% O2) environment. Compared to CON offspring, PH male offspring exhibited depression-like behaviors. Prenatal hypoxia resulted in significantly higher protein level of the oxygen-sensitive subunit of hypoxia-inducible factor (Hif-1α) and lower levels of Ten-eleven translocated methylcytosine dioxygenase 1 (Tet1), β-catenin, and downstream Dicer1-miRNAs pathway associated with depressive behavior. Mechanistically, prenatal hypoxia leads to Hif-1α binding to Tet1, which inhibits β-catenin binding to Tet1, leading to an increase in ubiquitination-dependent degradation of β-catenin and down-regulation of the β-catenin-Dicer1-miRNAs pathway. In addition, administration of the β-catenin-specific agonist SKL2001 or overexpressing virus ameliorated the down-regulation of β-catenin-Dicer1-miRNAs signaling and depression-like behavior in PH male offspring. These findings suggest that Hif-1α and β-catenin competition for Tet1 binding is involved in depression-like behaviors in PH offspring, and this study provides important data on the molecular mechanisms by which prenatal hypoxia might be involved in adult psychiatric disorders of fetal origin.

Redox-Driven Epigenetic Modifications in Sperm: Unraveling Paternal Influences on Embryo Development and Transgenerational Health

Male-factor infertility accounts for nearly half of all infertility cases, and mounting evidence points to oxidative stress as a pivotal driver of sperm dysfunction, genetic instability, and epigenetic dysregulation. In particular, the oxidative DNA lesion 8-hydroxy-2'-deoxyguanosine (8-OHdG) has emerged as a central mediator at the interface of DNA damage and epigenetic regulation. We discuss how this lesion can disrupt key epigenetic mechanisms such as DNA methylation, histone modifications, and small non-coding RNAs, thereby influencing fertilization outcomes, embryo development, and offspring health. We propose that the interplay between oxidative DNA damage and epigenetic reprogramming is further exacerbated by aging in both the paternal and maternal germlines, creating a "perfect storm" that increases the risk of heritable (epi)mutations. The consequences of unresolved oxidative lesions can thus persist beyond fertilization, contributing to transgenerational health risks. Finally, we explore the promise and potential pitfalls of antioxidant therapy as a strategy to mitigate sperm oxidative damage. While antioxidant supplementation may hold significant therapeutic value for men with subfertility experiencing elevated oxidative stress, a careful, personalized approach is essential to avoid reductive stress and unintended epigenetic disruptions. Recognizing the dual role of oxidative stress in shaping both the genome and the epigenome underscores the need for integrating redox biology into reproductive medicine, with the aim of improving fertility treatments and safeguarding the health of future generations.

Can the Supplementation of Oocytes with Extra Copies of mtDNA Impact Development Without Being Transmitted? A Molecular Account

The introduction of extra copies of mitochondrial DNA (mtDNA), whether autologous or heterologous, into oocytes at the time of fertilisation or through other assisted reproductive technologies, such as nuclear transfer, is a contentious issue. The primary focus has been on whether third-party mtDNA is transmitted to the offspring and if it impacts offspring health and well-being. However, little attention has focused on whether the introduction of extra copies of mtDNA will interfere with the balance established between the nuclear and mitochondrial genomes during oogenesis and as the developing embryo establishes its own epigenetic imprint that will influence mature offspring. Whilst we determined that sexually mature offspring generated through mtDNA supplementation did not inherit any-third party mtDNA, they exhibited differences in gene expression from three tissues derived from three separate embryonic lineages. This resulted in a number of pathways being affected. In each case, the differences were greater in the heterologous and autologous comparison than when comparing all supplemented offspring against non-supplemented offspring. Many of the changes in gene expression were coupled to differential DNA methylation across tissues, some of which were tissue-specific, with high levels observed in the heterologous against autologous comparison. An analysis of DNA methylation in blastocyst-stage embryos pointed to changes in patterns of DNA methylation that were transmitted through to the offspring. Our results indicated that extra copies of mtDNA may not be transmitted if introduced at low levels, but the changes induced by supplementation that occur in DNA methylation and gene expression in the blastocyst have a profound effect on tissues.

Transposition element MERVL regulates DNA demethylation through TET3 in oxidative-damaged mouse preimplantation embryos

Transposable elements (TEs) comprise approximately half of eukaryotic genomes and significantly contribute to genome plasticity. In this study, we focused on a specific TE, MERVL, which exhibits particular expression during the 2-cell stage and commonly serves as an indicator of embryonic totipotency. However, its precise role in embryo development remains mysterious. We utilized DRUG-seq to investigate the effects of oxidative damage on genes and TEs expression. Our findings revealed that exposure to hydrogen peroxide (H2O2) could induce DNA damage, apoptosis, and incomplete DNA demethylation in embryos, which were potentially associated with MERVL expression. To further explore its function, antisense nucleotides (ASO) targeting MERVL were constructed to knockdown the expression in early embryos. Notably, this knockdown led to the occurrence of DNA damage and apoptosis as early as the 2-cell stage, consequently reducing the number of embryos that could progress to the blastocyst stage. Moreover, we discovered that MERVL exerted an influence on the reprogramming of embryonic DNA methylation. In MERVL-deficient embryos, the activity of the DNA demethylase ten-eleven translocation 3 (TET3) was suppressed, resulting in impaired demethylation when compared to normal development. This impairment might underpin the mechanism that impacts embryonic development. Collectively, our study not only verified the crucial role of MERVL in embryonic development but also probed its regulatory function in DNA methylation reprogramming, thereby laying a solid foundation for further investigations into MERVL's role.

The Mammalian Oocyte: A Central Hub for Cellular Reprogramming and Stemness

The mammalian oocyte is pivotal in reproductive biology, acting as a central hub for cellular reprogramming and stemness. It uniquely contributes half of the zygotic nuclear genome and the entirety of the mitochondrial genome, ensuring individual development and health. Oocyte-mediated reprogramming, exemplified by nuclear transfer, resets somatic cell identity to achieve pluripotency and has transformative potential in regenerative medicine. This process is critical for understanding cellular differentiation, improving assisted reproductive technologies, and advancing cloning and stem cell research. During fertilization, the maternal-zygotic transition shifts developmental control from maternal factors to zygotic genome activation, establishing totipotency. Oocytes also harbor reprogramming factors that guide nuclear remodeling, epigenetic modifications, and metabolic reprogramming, enabling early embryogenesis. Structures like mitochondria, lipid droplets, and cytoplasmic lattices contribute to energy production, molecular regulation, and cellular organization. Recent insights into oocyte components, such as ooplasmic nanovesicles and endolysosomal vesicular assemblies (ELVAS), highlight their roles in maintaining cellular homeostasis, protein synthesis, and reprogramming efficiency. By unraveling the reprogramming mechanisms inherent in oocytes, we advance our understanding of cloning, cell differentiation, and stem cell therapy, highlighting their valuable significance in developmental biology and regenerative medicine.