Changes in histone H3 lysine 36 methylation in porcine oocytes and preimplantation embryos

Induction of autophagy in one-cell stage somatic cell nuclear transfer embryos improves preimplantation embryonic development in goat species

Autophagy is a lysosome-mediated catabolic pathway that is dependent on the mammalian target of rapamycin (mTOR). It plays a crucial role in the degradation of aged organelles and macromolecules. Several studies have explored the role of autophagy in embryonic genome activation and its significance during the early preimplantation development of mammals. In our study, we showed that autophagy is inhibited in one-cell stage SCNT embryos when compared to fertilized counterparts in goats. Notably, we found that 6-DMAP, a kinase inhibitor, reduces the phosphorylation of ERK1/2.This reduction correlates with a decrease in autophagy levels, as indicated by the presence of LC3 puncta in 6-DMAP treated embryos. To address the inhibition of autophagy in goat SCNT embryos, we induced autophagy using Rapamycin at concentrations of 10 and 100 nM for 6 hours, immediately following chemical activation. This induction led to a significant improvement in the development of goat SCNT embryos, as evidenced by an increased blastocyst rate compared to the control group. Our findings suggest that the induction of autophagy during early hours of one-cell stage embryos is critical for pre-implantation development in goat SCNT embryos warrant further investigation. This research opens new avenues for understanding the role of autophagy in embryonic development and its applications in reproductive biotechnology.

Effects of Glycine on epigenetic modification and early embryonic development in porcine oocytes exposed to monobutyl phthalate

Monobutyl phthalate (MBP) is the primary active metabolite of dibutyl phthalate (DBP), the key plasticizer component. A substantial body of evidence from studies conducted on both animals and humans indicates that MBP exposure could result in harmful impacts on toxicity pathways. In addition, it can seriously affect human and animal reproductive health. In our present study, we showed that exposure to MBP causes abnormal epigenetic modifications in porcine oocytes and failure of early embryonic development. However, glycine (Gly) can protect oocytes and early embryos from damage caused by MBP. Our study indicated a significant decrease in the percentage of porcine oocytes that reached the metaphase II (MII) phase when exposed to MBP. SET-domain-containing 2(SETD2)-mediated H3K36me3 histone methylation was detected, and the results showed that MBP significantly decreased the protein expression of H3K36me3 and SETD2. Moreover, the expression of the DNA break markers γH2AX and the mRNA expression of Asf1a, and Asf1b increased in the MBP group. The detection of DNA methylation marker proteins showed that MBP significantly increased the fluorescence intensity of 5-methylcytosine (5mC). The results from our RT-qPCR analysis demonstrated a significant decrease in the mRNA expression of the DNA methylation-related genes Dnmt1 and Dnmt3a, as well as the embryonic developmental potential-related genes Oct4 and Nanog, in porcine oocytes following exposure to MBP. Additionally, the mRNA expression of p53 significantly increased. Subsequently, the effects of MBP on early embryonic development were examined via parthenogenesis activation (PA) and in vitro fertilization (IVF). Exposure to MBP significantly impacted the development of embryos in both PA and IVF processes. The TUNEL staining data showed that MBP significantly increased embryonic apoptosis. However, Gly can ameliorate MBP-induced defects in oocyte epigenetic modifications and early embryonic development.

ISWI chromatin remodeling complexes recruit NSD2 and H3K36me2 in pericentromeric heterochromatin

Histone H3 lysine36 dimethylation (H3K36me2) is generally distributed in the gene body and euchromatic intergenic regions. However, we found that H3K36me2 is enriched in pericentromeric heterochromatin in some mouse cell lines. We here revealed the mechanism of heterochromatin targeting of H3K36me2. Among several H3K36 methyltransferases, NSD2 was responsible for inducing heterochromatic H3K36me2. Depletion and overexpression analyses of NSD2-associating proteins revealed that NSD2 recruitment to heterochromatin was mediated through the imitation switch (ISWI) chromatin remodeling complexes, such as BAZ1B-SMARCA5 (WICH), which directly binds to AT-rich DNA via a BAZ1B domain-containing AT-hook-like motifs. The abundance and stoichiometry of NSD2, SMARCA5, and BAZ1B could determine the localization of H3K36me2 in different cell types. In mouse embryos, H3K36me2 heterochromatin localization was observed at the two- to four-cell stages, suggesting its physiological relevance.

In vitro maturation using αMEM containing reduced NaCl enhances maturation and developmental competence of pig oocytes after somatic cell nuclear transfer

Background

Compared to medium containing 108 mM sodium chloride (NaCl), in vitro maturation (IVM) using a simple medium with reduced (61.6 mM) NaCl increases the cytoplasmic maturation and embryonic development of pig oocytes.

Objectives

This study determines the effect of a complex medium containing reduced NaCl on the IVM and embryonic development of pig oocytes.

Methods

Pig oocytes were matured in Minimum Essential Medium Eagle-alpha modification (αMEM) supplemented with 61.6 (61αMEM) or 108 (108αMEM) mM NaCl, and containing polyvinyl alcohol (PVA) (αMEMP) or pig follicular fluid (PFF) (αMEMF). Medium-199 (M199) served as the control for conventional IVM. Cumulus cell expansion, nuclear maturation, intra-oocyte glutathione (GSH) contents, size of perivitelline space (PVS), and embryonic development after parthenogenesis (PA) and somatic cell nuclear transfer (SCNT) were evaluated after IVM.

Results

Regardless of PVA or PFF supplementation, oocytes matured in 61αMEM showed increased intra-oocyte GSH contents and width of PVS (p < 0.05), as well as increased blastocyst formation (p < 0.05) after PA and SCNT, as compared to oocytes matured in 108αMEMP and M199. Under conditions of PFF-enriched αMEM, SCNT oocytes matured in 61αMEMF showed higher blastocyst formation (p < 0.05), compared to maturation in 108αMEMF and M199, whereas PA cultured oocytes showed no significant difference.

Conclusions

IVM in αMEM supplemented with reduced NaCl (61.6 mM) enhances the embryonic developmental competence subsequent to PA and SCNT, which attributes toward improved oocyte maturation.

The Epigenetics of Gametes and Early Embryos and Potential Long-Range Consequences in Livestock Species-Filling in the Picture With Epigenomic Analyses

The epigenome is dynamic and forged by epigenetic mechanisms, such as DNA methylation, histone modifications, chromatin remodeling, and non-coding RNA species. Increasing lines of evidence support the concept that certain acquired traits are derived from environmental exposure during early embryonic and fetal development, i.e., fetal programming, and can even be "memorized" in the germline as epigenetic information and transmitted to future generations. Advances in technology are now driving the global profiling and precise editing of germline and embryonic epigenomes, thereby improving our understanding of epigenetic regulation and inheritance. These achievements open new avenues for the development of technologies or potential management interventions to counteract adverse conditions or improve performance in livestock species. In this article, we review the epigenetic analyses (DNA methylation, histone modification, chromatin remodeling, and non-coding RNAs) of germ cells and embryos in mammalian livestock species (cattle, sheep, goats, and pigs) and the epigenetic determinants of gamete and embryo viability. We also discuss the effects of parental environmental exposures on the epigenetics of gametes and the early embryo, and evidence for transgenerational inheritance in livestock.

Changes of histone H3 lysine 23 acetylation and methylation in porcine somatic cells, oocytes and preimplantation embryos

Histone modifications play important roles in regulating the expression of developmental genes during preimplantation embryonic development. Here, we analyzed the temporal and spatial distribution of the acetylation and mono-, di- and tri-methylations of noncanonical histone H3 at lysine 23 (H3K23ac, H3K23me1, H3K23me2 and H3K23me3) during porcine oocyte maturation and pre-implantation development, as well as in porcine fetal fibroblasts. H3K23ac, -me1, -me2 and -me3 were enhanced in EdU-positive fetal fibroblasts (S-phase) compared to EdU-negative fetal fibroblasts (G1 and/or G2-phase). More than 91% of the DNA replication foci were well colocalized with H3K23 methylation sites in porcine fetal fibroblasts. H3K23ac and -me3 were detectable through oocyte meiotic resumption. After parthenogenic activation (PA), H3K23me3 was very weakly detected in the pronuclei of zygotes and the nuclei of blastocysts. After in vitro fertilization (IVF), no H3K23me3 signal was observed in the nuclei of IVF-derived embryos, with the exception of the residual polar bodies. In contrast, H3K23ac signals were clearly detected in the nuclei of PA- and IVF-derived blastocysts. The RNA polymerase inhibitor, actinomycin D, reduced the H3K23ac signal in porcine blastocysts. These findings may serve as a valuable reference for further studies of how H3K23 modifications contribute to the regulation of oocyte maturation and early embryonic development in mammals.

Ascorbic acid induces global epigenetic reprogramming to promote meiotic maturation and developmental competence of porcine oocytes

L-ascorbic acid (Vitamin C) can enhance the meiotic maturation and developmental competence of porcine oocytes, but the underlying molecular mechanism remains obscure. Here we show the role of ascorbic acid in regulating epigenetic status of both nucleic acids and chromatin to promote oocyte maturation and development in pigs. Supplementation of 250 μM L-ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AA2P) during in vitro maturation significantly enhanced the nuclear maturation (as indicated by higher rate of first polar body extrusion and increased Bmp15 mRNA level), reduced level of reactive oxygen species, and promoted developmental potency (higher cleavage and blastocyst rates of parthenotes, and decreased Bax and Caspase3 mRNA levels in blastocysts) of pig oocytes. AA2P treatment caused methylation erasure in mature oocytes on nucleic acids (5-methylcytosine (5 mC) and N ⁶ -methyladenosine (m⁶A)) and histones (Histone H3 trimethylations at lysines 27, H3K27me3), but establishment of histone H3 trimethylations at lysines 4 (H3K4me3) and 36 (H3K36me3). During the global methylation reprogramming process, levels of TET2 (mRNA and protein) and Dnmt3b (mRNA) were significantly elevated, but simultaneously DNMT3A (mRNA and protein), and also Hif-1α, Hif-2α, Tet3, Mettl14, Kdm5b and Eed (mRNA) were significantly inhibited. Our findings support that ascorbic acid can reprogram the methylation status of not only DNA and histone, but also RNA, to improve pig oocyte maturation and developmental competence.

Dynamic changes of SETD2, a histone H3K36 methyltransferase, in porcine oocytes, IVF and SCNT embryos

SETD2 (SET domain containing protein 2) acts as a histone H3 lysine 36 (H3K36)-specific methyltransferase and may play important roles in active gene transcription in human cells. However, its expression and role in porcine oocytes and preimplantation embryos are not well understood. Here, we used immunofluorescence and laser scanning confocal microscopy to examine SETD2 expression in porcine fetal fibroblasts, oocytes, and preimplantation embryos derived from in vitro fertilization (IVF), parthenogenetic activation (PA), and somatic cell nuclear transfer (SCNT). In porcine fetal fibroblasts, SETD2 expression was detected in interphase cells, but not in M (mitotic)-phase cells. The SETD2 signal was observed in non-surrounded nucleolus (NSN)-stage oocytes, but not in surrounded nucleolus (SN)-, metaphase I (MI)-, or metaphase II (MII)-stage oocytes. The SETD2 signal was detectable in sperm, and undetectable immediately after fertilization, detectable at the 2-cell stage, and peaked at the 4-cell stage of IVF embryos in which porcine embryonic genome is activated. Similar to the pattern found in IVF embryos, the SETD2 signal was absent from PA embryos at the 1-cell stage, but it was detected at the 2-cell stage and thereafter maintained to the blastocyst stage. Interestingly, unlike the IVF and PA embryos, the SETD2 signal was detected throughout the development of SCNT embryos, including at the 1-cell stage. These data suggest that SETD2 may be functional for embryonic gene transcription in porcine preimplantation embryos. It is further speculated that the aberrant expression of SETD2 at the 1-cell stage of porcine SCNT embryos may be a factor in the low efficiency of cloning in pig.

XIST Derepression in Active X Chromosome Hinders Pig Somatic Cell Nuclear Transfer

Pig cloning by somatic cell nuclear transfer (SCNT) remains extremely inefficient, and many cloned embryos undergo abnormal development. Here, by profiling transcriptome expression, we observed dysregulated chromosome-wide gene expression in every chromosome and identified a considerable number of genes that are aberrantly expressed in the abnormal cloned embryos. In particular, XIST, a long non-coding RNA gene, showed high ectopic expression in abnormal embryos. We also proved that nullification of the XIST gene in donor cells can normalize aberrant gene expression in cloned embryos and enhance long-term development capacity of the embryos. Furthermore, the increased quality of XIST-deficient embryos was associated with the global H3K9me3 reduction. Injection of H3K9me demethylase Kdm4A into NT embryos could improve the development of pre-implantation stage embryos. However, Kdm4A addition also induced XIST derepression in the active X chromosome and thus was not able to enhance the in vivo long-term developmental capacity of porcine NT embryos.

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Normal and abnormal pig SCNT embryos featured different transcriptome patterns

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Disrupting XIST gene in donor cells could enhance pig NT embryo development capacity

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Kdm4A injection was able to improve development of pig pre-implantation stage embryos

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Kdm4A addition caused XIST derepression and failed to improve pig cloning efficiency

DMBA acts on cumulus cells to desynchronize nuclear and cytoplasmic maturation of pig oocytes

As an environmental pollutant and carcinogen, 7,12-dimethylbenz[a]anthracene (DMBA) can destroy ovarian follicles at all developmental stages in rodents. However, the underlying molecular mechanism remains obscure. In the present study, we aim to address how DMBA affects the in vitro maturation and development of porcine oocytes. We discovered that for 20 μM DMBA-treated cumulus-oocyte complexes (COCs), the rate of oocyte germinal vesicle breakdown (GVBD) was significantly altered, and the extrusion rate of first polar body was increased. Moreover, oocytes from 20 μM DMBA-treated COCs had significant down-regulation of H3K9me3 and H3K27me3, up-regulation of H3K36me3, higher incidence of DNA double strand breaks (DSBs) and early apoptosis. In striking contrast, none of these changes happened to 20 μM DMBA-treated cumulus-denuded oocytes (CDOs). Furthermore, 20 μM DMBA treatment increased the reactive oxygen species (ROS) level, decreased mitochondrial membrane potential (Δ Ψm), and inhibited developmental competence for oocytes from both COC and CDO groups. Collectively, our data indicate DMBA could act on cumulus cells via the gap junction to disturb the synchronization of nuclear and ooplasmic maturation, and reduce the developmental competence of oocytes.

Genome-Wide Dynamic Profiling of Histone Methylation during Nuclear Transfer-Mediated Porcine Somatic Cell Reprogramming

The low full-term developmental efficiency of porcine somatic cell nuclear transfer (SCNT) embryos is mainly attributed to imperfect epigenetic reprogramming in the early embryos. However, dynamic expression patterns of histone methylation involved in epigenetic reprogramming progression during porcine SCNT embryo early development remain to be unknown. In this study, we characterized and compared the expression patterns of multiple histone methylation markers including transcriptionally repressive (H3K9me2, H3K9me3, H3K27me2, H3K27me3, H4K20me2 and H4K20me3) and active modifications (H3K4me2, H3K4me3, H3K36me2, H3K36me3, H3K79me2 and H3K79me3) in SCNT early embryos from different developmental stages with that from in vitro fertilization (IVF) counterparts. We found that the expression level of H3K9me2, H3K9me3 and H4K20me3 of SCNT embryos from 1-cell to 4-cell stages was significantly higher than that in the IVF embryos. We also detected a symmetric distribution pattern of H3K9me2 between inner cell mass (ICM) and trophectoderm (TE) in SCNT blastocysts. The expression level of H3K9me2 in both lineages from SCNT expanded blastocyst onwards was significantly higher than that in IVF counterparts. The expression level of H4K20me2 was significantly lower in SCNT embryos from morula to blastocyst stage compared with IVF embryos. However, no aberrant dynamic reprogramming of H3K27me2/3 occurred during early developmental stages of SCNT embryos. The expression of H3K4me3 was higher in SCNT embryos at 4-cell stage than that of IVF embryos. H3K4me2 expression in SCNT embryos from 8-cell stage to blastocyst stage was lower than that in the IVF embryos. Dynamic patterns of other active histone methylation markers were similar between SCNT and IVF embryos. Taken together, histone methylation exhibited developmentally stage-specific abnormal expression patterns in porcine SCNT early embryos.

Histone methyltransferases: novel targets for tumor and developmental defects

Histone lysine methylation plays a critical role in epigenetic regulation of eukaryotes. To date, studies have shown that lysine residues of K4, K9, K27, K36 and K79 in histone H3 and K20 in histone H4 can be modified by histone methyltransferases (HMTs). Such histone methylation can specifically activate or repress the transcriptional activity to play a key role in gene expression/regulation and biological genetics. Importantly, abnormities of patterns or levels of histone methylation in higher eukaryotes may result in tumorigenesis and developmental defects, suggesting histone methylation will be one of the important targets or markers for treating these diseases. This review will outline the structural characteristics, active sites and specificity of HMTs, correlation between histone methylation and human diseases and lay special emphasis on the progress of the research on H3K36 methylation.