BIX-01294 increases pig cloning efficiency by improving epigenetic reprogramming of somatic cell nuclei

Pioneer factors: nature or nurture?

Chromatin is densely packed with nucleosomes, which limits the accessibility of many chromatin-associated proteins. Pioneer factors (PFs) are usually viewed as a special group of sequence-specific transcription factors (TFs) that can recognize nucleosome-embedded motifs, invade compact chromatin, and generate open chromatin regions. Through this process, PFs initiate a cascade of events that play key roles in gene regulation and cell differentiation. A current debate in the field is if PFs belong to a unique subset of TFs with intrinsic "pioneering activity", or if all TFs have the potential to function as PFs within certain cellular contexts. There are also different views regarding the key feature(s) that define pioneering activity. In this review, we present evidence from the literature related to these alternative views and discuss how to potentially reconcile them. It is possible that both intrinsic properties, like tight nucleosome binding and structural compatibility, and cellular conditions, like concentration and co-factor availability, are important for PF function.

Reduction of H3K9 methylation by G9a inhibitors improves the development of mouse SCNT embryos

Removal of somatic histone H3 lysine 9 trimethylation (H3K9me3) from the embryonic genome can improve the efficiency of mammalian cloning using somatic cell nuclear transfer (SCNT). However, this strategy involves the injection of histone demethylase mRNA into embryos, which is limiting because of its invasive and labor-consuming nature. Here, we report that treatment with an inhibitor of G9a (G9ai), the major histone methyltransferase that introduces H3K9me1/2 in mammals, greatly improved the development of mouse SCNT embryos. Intriguingly, G9ai caused an immediate reduction of H3K9me1/2, a secondary loss of H3K9me3 in SCNT embryos, and increased the birth rate of cloned pups about 5-fold (up to 3.9%). G9ai combined with the histone deacetylase inhibitor trichostatin A further improved this rate to 14.5%. Mechanistically, G9ai and TSA synergistically enhanced H3K9me3 demethylation and boosted zygotic genome activation. Thus, we established an easy, highly effective SCNT protocol that would enhance future cloning research and applications.

Chemically induced reprogramming to reverse cellular aging

A hallmark of eukaryotic aging is a loss of epigenetic information, a process that can be reversed. We have previously shown that the ectopic induction of the Yamanaka factors OCT4, SOX2, and KLF4 (OSK) in mammals can restore youthful DNA methylation patterns, transcript profiles, and tissue function, without erasing cellular identity, a process that requires active DNA demethylation. To screen for molecules that reverse cellular aging and rejuvenate human cells without altering the genome, we developed high-throughput cell-based assays that distinguish young from old and senescent cells, including transcription-based aging clocks and a real-time nucleocytoplasmic compartmentalization (NCC) assay. We identify six chemical cocktails, which, in less than a week and without compromising cellular identity, restore a youthful genome-wide transcript profile and reverse transcriptomic age. Thus, rejuvenation by age reversal can be achieved, not only by genetic, but also chemical means.

Plants and Small Molecules: An Up-and-Coming Synergy

The emergence of Arabidopsis thaliana as a model system has led to a rapid and wide improvement in molecular genetics techniques for studying gene function and regulation. However, there are still several drawbacks that cannot be easily solved with molecular genetic approaches, such as the study of unfriendly species, which are of increasing agronomic interest but are not easily transformed, thus are not prone to many molecular techniques. Chemical genetics represents a methodology able to fill this gap. Chemical genetics lies between chemistry and biology and relies on small molecules to phenocopy genetic mutations addressing specific targets. Advances in recent decades have greatly improved both target specificity and activity, expanding the application of this approach to any biological process. As for classical genetics, chemical genetics also proceeds with a forward or reverse approach depending on the nature of the study. In this review, we addressed this topic in the study of plant photomorphogenesis, stress responses and epigenetic processes. We have dealt with some cases of repurposing compounds whose activity has been previously proven in human cells and, conversely, studies where plants have been a tool for the characterization of small molecules. In addition, we delved into the chemical synthesis and improvement of some of the compounds described.

Effects of alpha lipoic acid treatment during in vitro maturation on the development of porcine somatic cell nuclear transfer embryos

Oxidative stress influences the embryo production efficiency in vitro. We investigated the effects of alpha lipoic acid (ALA) treatment during the in vitro maturation (IVM) period on the porcine somatic cell nuclear transfer (SCNT) embryo production. After IVM, maturation rates of the 12.5- and 25-μM ALA-treated groups were not significantly different from those of the 0-μM ALA-treated group. Compared to those in the 0-μM ALA-treated group, the reactive oxygen species and glutathione levels were significantly decreased and increased, respectively, in the cytoplasm of matured oocytes in the 12.5-50-μM ALA-treated groups. Apoptosis rate in cumulus cells after IVM was significantly lower in the 12.5-50-μM ALA-treated groups than in the 0-μM ALA-treated group. Blastocyst formation rate was significantly higher in parthenogenetic oocytes treated with 12.5-μM ALA than in the 0-, 25-, and 50-μM ALA-treated groups. Similarly, in SCNT embryos, the 12.5-μM ALA-treated group showed a significantly higher blastocyst formation rate than the 0-μM ALA-treated group. Apoptosis rate in SCNT blastocysts was significantly decreased by 12.5-μM ALA treatment. The results showed that treatment with 12.5-μM ALA during IVM improves porcine SCNT embryo development and partial quality.

2-Cell-like Cells: An Avenue for Improving SCNT Efficiency

After fertilization, the zygote genome undergoes dramatic structural reorganization to ensure the establishment of totipotency, and then the totipotent potential of the zygote or 2-cell-stage embryo progressively declines. However, cellular potency is not always a one-way street. Specifically, a small number of embryonic stem cells (ESCs) occasionally overcome epigenetic barriers and transiently convert to a totipotent status. Despite the significant potential of the somatic cell nuclear transfer (SCNT) technique, the establishment of totipotency is often deficient in cloned embryos. Because of this phenomenon, the question arises as to whether strategies attempting to induce 2-cell-like cells (2CLCs) can provide practical applications, such as reprogramming of somatic cell nuclei. Inspired by strategies that convert ESCs into 2CLCs, we hypothesized that there will be a similar pathway by which cloned embryos can establish totipotent status after SCNT. In this review, we provide a snapshot of the practical strategies utilized to induce 2CLCs during investigations of the development of cloned embryos. The 2CLCs have similar transcriptome and chromatin features to that of 2-cell-stage embryos, and we propose that 2CLCs, already a valuable in vitro model for dissecting totipotency, will provide new opportunities to improve SCNT efficiency.

Epigenetic manipulation to improve mouse SCNT embryonic development

Cloned mammals can be achieved through somatic cell nuclear transfer (SCNT), which involves reprogramming of differentiated somatic cells into a totipotent state. However, low cloning efficiency hampers its application severely. Cloned embryos have the same DNA as donor somatic cells. Therefore, incomplete epigenetic reprogramming accounts for low development of cloned embryos. In this review, we describe recent epigenetic barriers in SCNT embryos and strategies to correct these epigenetic defects and avoid the occurrence of abnormalities in cloned animals.

Enhancement of Chromatin and Epigenetic Reprogramming in Porcine SCNT Embryos—Progresses and Perspectives

Over the last 25 years, cloned animals have been produced by transferring somatic cell nuclei into enucleated oocytes (SCNT) in more than 20 mammalian species. Among domestic animals, pigs are likely the leading species in the number of clones produced by SCNT. The greater interest in pig cloning has two main reasons, its relevance for food production and as its use as a suitable model in biomedical applications. Recognized progress in animal cloning has been attained over time, but the overall efficiency of SCNT in pigs remains very low, based on the rate of healthy, live born piglets following embryo transfer. Accumulating evidence from studies in mice and other species indicate that new strategies for promoting chromatin and epigenetic reprogramming may represent the beginning of a new era for pig cloning.

A diverse English keyword search reveals the value of scriptaid treatment for porcine embryo development following somatic cell nuclear transfer

CONTEXT

Incomplete epigenetic reprogramming of histone deacetylation (HDAC) is one of the main reasons for the low efficiency of somatic cell nuclear transfer (SCNT). Scriptaid is a synthetic HDAC inhibitor (HDACi) that may improve the efficiency of porcine SCNT.

AIMS

This study aimed to determine whether scriptaid increases the number of blastocyst cells or the cleavage rate.

METHODS

We conducted a meta-analysis of the pertinent literature published over the past decade.

KEY RESULTS

A total of 73 relevant papers were retrieved using a diverse English keyword search, and 11 articles were used for the meta-analysis. Scriptaid was positively correlated with blastocyst rate but had no effect on cleavage rate or blastocyst cell number. A subgroup analysis of blastocyst cell number showed that the staining method was the source of the heterogeneity.

CONCLUSIONS

In SCNT embryos, scriptaid treatment after activation can promote embryonic development, but there may be adverse effects on early development.

IMPLICATIONS

HDACi research should focus on SCNT birth efficiency.

Production of Pigs From Porcine Embryos Generated in vitro

Generating porcine embryos in vitro is a critical process for creating genetically modified pigs as agricultural and biomedical models; however, these embryo technologies have been scarcely applied by the swine industry. Currently, the primary issue with in vitro-produced porcine embryos is low pregnancy rate after transfer and small litter size, which may be exasperated by micromanipulation procedures. Thus, in this review, we discuss improvements that have been made to the in vitro porcine embryo production system to increase the number of live piglets per pregnancy as well as abnormalities in the embryos and piglets that may arise from in vitro culture and manipulation techniques. Furthermore, we examine areas related to embryo production and transfer where improvements are warranted that will have direct applications for increasing pregnancy rate after transfer and the number of live born piglets per litter.

Strategies to Improve the Efficiency of Somatic Cell Nuclear Transfer

Mammalian oocytes can reprogram differentiated somatic cells into a totipotent state through somatic cell nuclear transfer (SCNT), which is known as cloning. Although many mammalian species have been successfully cloned, the majority of cloned embryos failed to develop to term, resulting in the overall cloning efficiency being still low. There are many factors contributing to the cloning success. Aberrant epigenetic reprogramming is a major cause for the developmental failure of cloned embryos and abnormalities in the cloned offspring. Numerous research groups attempted multiple strategies to technically improve each step of the SCNT procedure and rescue abnormal epigenetic reprogramming by modulating DNA methylation and histone modifications, overexpression or repression of embryonic-related genes, etc. Here, we review the recent approaches for technical SCNT improvement and ameliorating epigenetic modifications in donor cells, oocytes, and cloned embryos in order to enhance cloning efficiency.

Combined Chaetocin/Trichostatin A Treatment Improves the Epigenetic Modification and Developmental Competence of Porcine Somatic Cell Nuclear Transfer Embryos

Developmental defects in somatic cell nuclear transfer (SCNT) embryos are principally attributable to incomplete epigenetic reprogramming. Small-molecule inhibitors such as histone methyltransferase inhibitors (HMTi) and histone deacetylase inhibitors (HDACi) have been used to improve reprogramming efficiency of SCNT embryos. However, their possible synergistic effect on epigenetic reprogramming has not been studied. In this study, we explored whether combined treatment with an HMTi (chaetocin) and an HDACi (trichostatin A; TSA) synergistically enhanced epigenetic reprogramming and the developmental competence of porcine SCNT embryos. Chaetocin, TSA, and the combination significantly increased the cleavage and blastocyst formation rate, hatching/hatched blastocyst rate, and cell numbers and survival rate compared to control embryos. In particular, the combined treatment improved the rate of development to blastocysts more so than chaetocin or TSA alone. TSA and combined chaetocin/TSA significantly reduced the H3K9me3 levels and increased the H3K9ac levels in SCNT embryos, although chaetocin alone significantly reduced only the H3K9me3 levels. Moreover, these inhibitors also decreased global DNA methylation in SCNT embryos. In addition, the expression of zygotic genome activation- and imprinting-related genes was increased by chaetocin or TSA, and more so by the combination, to levels similar to those of in vitro-fertilized embryos. These results suggest that combined chaetocin/TSA have synergistic effects on improving the developmental competences by regulating epigenetic reprogramming and correcting developmental potential-related gene expression in porcine SCNT embryos. Therefore, these strategies may contribute to the generation of transgenic pigs for biomedical research.

CRISPR/Cas13d-mediated efficient KDM5B mRNA knockdown in porcine somatic cells and parthenogenetic embryos

An efficient mRNA knockdown strategy is needed to explore gene function in cells and embryos, especially to understand the process of maternal mRNA decay during early embryo development. Cas13, a novel RNA-targeting CRISPR effector protein, could bind and cleave complementary single-strand RNA, which has been employed for mRNA knockdown in mouse and human cells and RNA-virus interference in plants. Cas13 has not yet been reported to be used in pigs. In the current study, we explored the feasibility of CRISPR/Cas13d-mediated endogenous RNA knockdown in pigs. KDM5B, a histone demethylase of H3K4me3, was downregulated at the transcriptional level by 50% with CRISPR/Cas13d in porcine fibroblast cells. Knockdown of KDM5B-induced H3K4me3 expression and decreased the abundance of H3K27me3, H3K9me3, H3K4ac, H4K8ac, and H4K12ac. These changes affected cell proliferation and cell cycle. Furthermore, stable integration of the CRISPR/Cas13d system into the porcine genome resulted in the continuous expression of Cas13d and persistent knockdown of KDM5B. Finally, the RNA-targeting potential of Cas13d was further validated in porcine parthenogenetic embryos. By microinjection of Cas13d mRNA and gRNA targeting KDM5B into porcine oocytes, the expression of KDM5B was downregulated, the abundance of H3K4me3 increased as expected, and the expression of embryonic development-related genes was changed accordingly. These results indicate that CRISPR/Cas13d provides an easily programmable platform for spatiotemporal transcriptional manipulation in pigs.

Histone Demethylase KDM4D Could Improve the Developmental Competence of Buffalo (Bubalus Bubalis) Somatic Cell Nuclear Transfer (SCNT) Embryos

Somatic cell nuclear transfer (SCNT) holds vast potential in agriculture. However, its applications are still limited by its low efficiency. Histone 3 lysine 9 trimethylation (H3K9me3) was identified as an epigenetic barrier for this. Histone demethylase KDM4D could regulate the level of H3K9me3. However, its effects on buffalo SCNT embryos are still unclear. Thus, we performed this study to explore the effects and underlying mechanism of KDM4D on buffalo SCNT embryos. The results revealed that compared with the IVF embryos, the expression level of KDM4D in SCNT embryos was significantly lower at 8- and 16-cell stage, while the level of H3K9me3 in SCNT embryos was significantly higher at 2-cell, 8-cell, and blastocyst stage. Microinjection of KDM4D mRNA could promote the developmental ability of buffalo SCNT embryos. Furthermore, the expression level of ZGA-related genes such as ZSCAN5B, SNAI1, eIF-3a, and TRC at the 8-cell stage was significantly increased. Meanwhile, the pluripotency-related genes like POU5F1, SOX2, and NANOG were also significantly promoted at the blastocyst stage. The results were reversed after KDM4D was inhibited. Altogether, these results revealed that KDM4D could correct the H3K9me3 level, increase the expression level of ZGA and pluripotency-related genes, and finally, promote the developmental competence of buffalo SCNT embryos.

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.

Manipulating the Epigenome in Nuclear Transfer Cloning: Where, When and How

The nucleus of a differentiated cell can be reprogrammed to a totipotent state by exposure to the cytoplasm of an enucleated oocyte, and the reconstructed nuclear transfer embryo can give rise to an entire organism. Somatic cell nuclear transfer (SCNT) has important implications in animal biotechnology and provides a unique model for studying epigenetic barriers to successful nuclear reprogramming and for testing novel concepts to overcome them. While initial strategies aimed at modulating the global DNA methylation level and states of various histone protein modifications, recent studies use evidence-based approaches to influence specific epigenetic mechanisms in a targeted manner. In this review, we describe-based on the growing number of reports published during recent decades-in detail where, when, and how manipulations of the epigenome of donor cells and reconstructed SCNT embryos can be performed to optimize the process of molecular reprogramming and the outcome of nuclear transfer cloning.

Assessment of the Growth and Reproductive Performance of Cloned Pietrain Boars

How to maximize the use of the genetic merits of the high-ranking boars (also called superior ones) is a considerable question in the pig breeding industry, considering the money and time spent on selection. Somatic cell nuclear transfer (SCNT) is one of the potential ways to answer the question, which can be applied to produce clones with genetic resources of superior boar for the production of commercial pigs. For practical application, it is essential to investigate whether the clones and their progeny keep behaving better than the "normal boars", considering that in vitro culture and transfer manipulation would cause a series of harmful effects to the development of clones. In this study, 59,061 cloned embryos were transferred into 250 recipient sows to produce the clones of superior Pietrain boars. The growth performance of 12 clones and 36 non-clones and the semen quality of 19 clones and 28 non-clones were compared. The reproductive performance of 21 clones and 25 non-clones were also tested. Furthermore, we made a comparison in the growth performance between 466 progeny of the clones and 822 progeny of the non-clones. Our results showed that no significant difference in semen quality and reproductive performance was observed between the clones and the non-clones, although the clones grew slower and exhibited smaller body size than the non-clones. The F1 progeny of the clones showed a greater growth rate than the non-clones. Our results demonstrated through the large animal population showed that SCNT manipulation resulted in a low growth rate and small body size, but the clones could normally produce F1 progeny with excellent growth traits to bring more economic benefits. Therefore, SCNT could be effective in enlarging the merit genetics of the superior boars and increasing the economic benefits in pig reproduction and breeding.

Chaetocin Improves Pig Cloning Efficiency by Enhancing Epigenetic Reprogramming and Autophagic Activity

Efficient epigenetic reprogramming is crucial for the in vitro development of mammalian somatic cell nuclear transfer (SCNT) embryos. The aberrant levels of histone H3 lysine 9 trimethylation (H3K9me3) is an epigenetic barrier. In this study, we evaluated the effects of chaetocin, an H3K9me3-specific methyltransferase inhibitor, on the epigenetic reprogramming and developmental competence of porcine SCNT embryos. The SCNT embryos showed abnormal levels of H3K9me3 at the pronuclear, two-cell, and four-cell stages compared to in vitro fertilized embryos. Moreover, the expression levels of H3K9me3-specific methyltransferases (suv39h1 and suv39h2) and DNA methyltransferases (DNMT1, DNMT3a, and DNMT3b) were higher in SCNT embryos. Treatment with 0.5 nM chaetocin for 24 h after activation significantly increased the developmental competence of SCNT embryos in terms of the cleavage rate, blastocyst formation rate, hatching rate, cell number, expression of pluripotency-related genes, and cell survival rate. In particular, chaetocin enhanced epigenetic reprogramming by reducing the H3K9me3 and 5-methylcytosine levels and restoring the abnormal expression of H3K9me3-specific methyltransferases and DNA methyltransferases. Chaetocin induced autophagic activity, leading to a significant reduction in maternal mRNA levels in embryos at the pronuclear and two-cell stages. These findings revealed that chaetocin enhanced the developmental competence of porcine SCNT embryos by regulating epigenetic reprogramming and autophagic activity and so could be used to enhance the production of transgenic pigs for biomedical research.

Seminal Plasma Induces Overexpression of Genes Associated with Embryo Development and Implantation in Day-6 Porcine Blastocysts

The infusion of boar seminal plasma (SP) before artificial insemination (AI) positively alters the expression of endometrial genes and pathways involved in embryo development. This study aimed to determine which transcriptome changes occur in preimplantation embryos in response to SP infusions during estrus. Postweaning estrus sows received 40-mL intrauterine infusions of either SP (N = 6) or BTS extender (control group; N = 6) 30 min before each of two post-cervical AIs. On Day 6, embryos were surgically collected and analyzed for differential gene expression. Microarray analysis of embryos revealed 210 annotated genes, differentially expressed (p-value < 0.05 and fold change </> 2) in SP-blastocysts, compared to controls. Most of these genes were associated with biological, cellular, metabolic and developmental processes. The pathways enriched among the upregulated genes related to signal transduction, cellular processes and the endocrine system. Among altered genes involved in these pathways, the SP-group showed a conspicuous overexpression of ApoA-I, CDK1, MAPK1, SMAD2, PRKAA1 and RICTOR, with reported key roles in embryo development, implantation, or progression of pregnancy. In conclusion, the results demonstrate that SP infusions prior to AI upregulates the expression of embryo development related genes in Day 6 pig embryos.

CRISPR/Cas9-Mediated Biallelic Knockout of IRX3 Reduces the Production and Survival of Somatic Cell-Cloned Bama Minipigs

Bama minipigs are a local pig breed that is unique to China and has a high development and utilization value. However, its high fat content, low feed utilization rate, and slow growth rate have limited its popularity and utilization. Compared with the long breeding cycle and high cost of traditional genetic breeding of pigs, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) endonuclease 9 system (CRISPR/Cas9)-mediated gene editing can cost-effectively implement targeted mutations in animal genomes, thereby providing a powerful tool for rapid improvement of the economic traits of Bama minipigs. The iroquois homeobox 3 (IRX3) gene has been implicated in human obesity. Mouse experiments have shown that knocking out IRX3 significantly enhances basal metabolism, reduces fat content, and controls body mass and composition. This study aimed to knock out IRX3 using the CRISPR/Cas9 gene editing method to breed Bama minipigs with significantly reduced fat content. First, the CRISPR/Cas9 gene editing method was used to efficiently obtain IRX3-/- cells. Then, the gene-edited cells were used as donor cells to produce surviving IRX3-/- Bama minipigs using somatic cell cloning. The results show that the use of IRX3-/- cells as donor cells for the production of somatic cell-cloned pigs results in a significant decrease in the average live litter size and a significant increase in the average number of stillbirths. Moreover, the birth weight of surviving IRX3-/- somatic cell-cloned pigs is significantly lower, and viability is poor such that all piglets die shortly after birth. Therefore, the preliminary results of this study suggest that IRX3 may have important biological functions in pigs, and IRX3 should not be used as a gene editing target to reduce fat content in Bama minipigs. Moreover, this study shows that knocking out IRX3 does not favor the survival of pigs, and whether targeted regulation of IRX3 in the treatment of human obesity will also induce severe adverse consequences requires further investigation.

Zebularine significantly improves the preimplantation development of ovine somatic cell nuclear transfer embryos

Aberrant DNA methylation reduces the developmental competence of mammalian somatic cell nuclear transfer (SCNT) embryos. Thus, hypomethylation-associated drugs are beneficial for improving reprogramming efficiency. Therefore, in the present study we investigated the effect of zebularine, a relatively novel DNA methyltransferase inhibitor, on the developmental potential of ovine SCNT embryos. First, reduced overall DNA methylation patterns and gene-specific DNA methylation levels at the promoter regions of pluripotency genes (octamer-binding transcription factor 4 (Oct4), SRY (sex determining region Y)-box 2 (Sox2) and Nanog) were found in zebularine-treated cumulus cells. In addition, the DNA methylation levels in SCNT embryos derived from zebularine-treated cumulus cells were significantly reduced at the 2-, 4-, 8-cell, and blastocyst stages compared with their corresponding controls (P<0.05). The blastocyst rate was significantly improved in SCNT embryos reconstructed by the cumulus donor cells treated with 5nM zebularine for 12h compared with the control group (25.4±1.6 vs 11.8±1.7%, P<0.05). Moreover, the abundance of Oct4 and Sox2 mRNA was significantly increased during the preimplantation stages after zebularine treatment (P<0.05). In conclusion, the results indicate that, in an ovine model, zebularine decreases overall DNA methylation levels in donor cumulus cells and reconstructed embryos, downregulates the DNA methylation profile in the promoter region of pluripotency genes in donor cells and ultimately elevates the expression of pluripotency genes in the reconstructed embryos, which can lead to improved development of SCNT embryos.

Improvement in the in vitro development of cloned pig embryos after kdm4a overexpression and an H3K9me3 methyltransferase inhibitor treatment

Aberrant epigenetic reprogramming is a major cause of the developmental failure of embryos after somatic cell nuclear transfer (SCNT). Histone H3 lysine 9 trimethylation (H3K9me3), a histone marker of transcriptional repression, is considered a key barrier to the development of cloned embryos. In the present study, H3K9me3 levels were much higher in SCNT embryos than IVF embryos at the 4-cell and 2-cell stages. The microinjection of the kdm4a mRNA encoding an H3K9me3 demethylase significantly increased the developmental efficiency of cloned porcine embryos. Moreover, we evaluated the effect of chaetocin, an inhibitor of histone methyltransferases suv39h1/2, on SCNT embryo development. Chaetocin did not suppress the H3K9me3 modification in porcine embryonic fibroblast (PEF) but downregulated the expression of suv39h1, suv39h2, and kdm4d. However, 10 nM chaetocin treatment efficiently decreased the H3K9me3 level in cloned embryos. Importantly, a chaetocin treatment at the 4-cell stage for 6 h significantly increased the blastocyst rate and total cell numbers. Furthermore, the inhibitor treatment upregulated the expression of related developmental genes. In summary, both overexpression of kdm4a and treatment with a suv39h1/2 inhibitor improve the epigenetic reprogramming of cloned embryos and further improve the developmental competence in vitro.

Expression of pluripotency-related genes is highly dependent on trichostatin A-assisted epigenomic modulation of porcine mesenchymal stem cells analysed for apoptosis and subsequently used for generating cloned embryos

The present study sought to examine whether trichostatin A (TSA)-assisted epigenetic transformation of porcine bone marrow (BM)-derived mesenchymal stem cells (BM-MSCs) affects the transcriptional activities of pluripotency-related genes (Oct4, Nanog, c-Myc, Sox2 and Rex1), multipotent stemness-related gene (Nestin) and anti-apoptotic/anti-senescence-related gene (Survivin). Epigenetically transformed or non-transformed BM-MSCs that had been transcriptionally profiled by qRT-PCR and had been analysed for different stages of apoptosis progression provided a source of nuclear donor cells for the in vitro production of cloned pig embryos. TSA-mediated epigenomic modulation has been found to enhance the multipotency extent, stemness and intracellular anti-ageing properties of porcine BM-MSCs. This has been confirmed by the relative abundances for Nanog, c-Myc Rex1, Sox2 and Survivin mRNAs in TSA-exposed BM-MSCs that turned out to be significantly higher than those of TSA-unexposed BM-MSCs. Additionally, TSA-assisted epigenomic modulation of BM-MSCs did not impact the caspase-8 activity, Bax protein expression and the incidence of TUNEL-positive cells. In conclusion, the considerably elevated quantitative profiles of Sox2, Rex1, c-Myc, Nanog and Survivin mRNA transcripts seem to trigger improved reprogrammability of TSA-treated BM-MSC nuclei in cloned pig embryos that thereby displayed remarkably increased blastocyst formation rates as compared to those noticed for embryos derived from TSA-untreated BM-MSCs.

Effects of polyunsaturated fatty acids on the development of pig oocytes in vitro following parthenogenetic activation and on the lipid content of oocytes and embryos

As oocytes and embryos of pigs have greater lipid content in the cytoplasm than those of other species, supplementation of the medium for in vitro maturation (IVM) of oocytes with omega-3 polyunsaturated fatty acids (PUFA) may help to improve embryo development. This study was conducted to evaluate effects of the inclusion of the docosaexaenoic (DHA) and of the eicosapentaenoic acids (EPA) in the IVM medium on the development of pig oocytes and on the lipid content of oocytes and embryos. In all experiments, control media consisted of porcine follicular fluid and oocytes were activated through parthenogenesis. In Experiment 1, there were four treatments for each PUFA: one control; and three treatments including EPA or DHA in the IVM medium at 12.5 μM, 25.0 μM and 50.0 μM). In Experiment 2, inclusion of 50 μM DHA was compared against the control. Cleavage rates in the IVM medium including 12.5 μM EPA and blastocyst development rates in media at any EPA concentration were less than for the control in Experiment 1 (P <  0.05). Compared to the control, inclusion of 50 μM DHA in the IVM medium was related to greater cleavage rates and greater number of embryo cells, in Experiment 1, and lesser lipid content in oocytes after 22 and 44 h and in embryos after 7 days, in Experiment 2 (both P <  0.05). Addition of DHA in the IVM medium may benefit the development of pig oocytes, but EPA appears to be cytotoxic.

Expression of polo-like kinase 1 in pre-implantation stage murine somatic cell nuclear transfer embryos

Somatic cell nuclear transfer (SCNT) has various applications in research, as well as in the medical field and animal husbandry. However, the efficiency of SCNT is low and the accurate mechanism of SCNT in murine embryo development is unreported. In general, the developmental rate of SCNT murine embryos is lower than in vivo counterparts. In previous studies, polo-like kinase 1 (Plk1) was reported to be a crucial element in cell division including centrosome maturation, cytokinesis, and spindle formation. In an initial series of experiments in this study, BI2536, a Plk1 inhibitor, was treated to in vivo-fertilized embryos and the embryos failed to develop beyond the 2-cell stage. This confirmed previous findings that Plk1 is crucial for the first mitotic division of murine embryos. Next, we investigated Plk1's localization and intensity by immunofluorescence analysis. In contrast to normally developed embryos, SCNT murine embryos that failed to develop exhibited two types of Plk1 expressions; a low Plk1 expression pattern and ectopic expression of Plk1. The results show that Plk1 has a critical role in SCNT murine embryos. In conclusion, this study demonstrated that the SCNT murine embryos fail to develop beyond the 2-cell stage, and the embryos show abnormal Plk1 expression patterns, which may one of the main causes of developmental failure of early SCNT murine embryos.

H3K27me3 is an epigenetic barrier while KDM6A overexpression improves nuclear reprogramming efficiency

Aberrant epigenetic reprogramming is a major factor of developmental failure of cloned embryos. Histone H3 lysine 27 trimethylation (H3K27me3), a histone mark for transcriptional repression, plays important roles in mammalian embryonic development and induced pluripotent stem cell (iPSC) generation. The global loss of H3K27me3 marks may facilitate iPSC generation in mice and humans. However, the H3K27me3 level and its role in bovine somatic cell nuclear transfer (SCNT) reprogramming remain poorly understood. Here, we show that SCNT embryos exhibit global H3K27me3 hypermethylation from the 2- to 8-cell stage and that its removal by ectopically expressed H3K27me3 lysine demethylase (KDM)6A greatly improves nuclear reprogramming efficiency. In contrast, H3K27me3 reduction by H3K27me3 methylase enhancer of zeste 2 polycomb repressive complex knockdown or donor cell treatment with the enhancer of zeste 2 polycomb repressive complex-selective inhibitor GSK343 suppressed blastocyst formation by SCNT embryos. KDM6A overexpression enhanced the transcription of genes involved in cell adhesion and cellular metabolism and X-linked genes. Furthermore, we identified methyl-CpG-binding domain protein 3-like 2, which was reactivated by KDM6A, as a factor that is required for effective reprogramming in bovines. These results show that H3K27me3 functions as an epigenetic barrier and that KDM6A overexpression improves SCNT efficiency by facilitating transcriptional reprogramming.-Zhou, C., Wang, Y., Zhang, J., Su, J., An, Q., Liu, X., Zhang, M., Wang, Y., Liu, J., Zhang, Y. H3K27me3 is an epigenetic barrier while KDM6A overexpression improves nuclear reprogramming efficiency.

The effect of cell penetrating peptide-conjugated coactivator-associated arginine methyltransferase 1 (CPP-CARM1) on the cloned mouse embryonic development

Abnormalities in gene expression that negatively affect embryonic development are frequently observed in cloned embryos generated by somatic cell nuclear transfer (SCNT). In the present study, we successfully produced a cell-penetrating peptide (CPP)-conjugated with coactivator-associated arginine methyltransferase 1 (CARM1) protein from mammalian cells and confirmed introduction into donor somatic cells and cloned 8-cell embryos within 3 hours after addition to culture medium. In addition, H3R17 dimethylation and embryonic development up to the blastocyst stage were increased in the group treated with exogenous CPP-CARM1 protein compared with the untreated group (control). Interestingly, the number of total cells and trophectoderm in blastocysts as well as implantation rate were significantly increased in the CPP-CARM1 protein-treated group. However, the cell number of inner cell mass (ICM) was not changed compared with the control group; similarly, expression of pluripotency-related genes Oct4 and Nanog (ICM markers) was not significantly different between groups. On the other hand, expression of the implantation-related gene Cdx2 (trophectoderm marker) was transiently increased after treatment with CPP-CARM1 protein. On the basis of these results, we conclude that supplementation with exogenous CPP-CARM1 protein improves embryonic development of cloned embryos through regulation of histone methylation and gene expression. In addition, our results suggest that CPP-CARM1 protein may be a useful tool for strengthening implantation of mammalian embryos.

Can Reprogramming of Overall Epigenetic Memory and Specific Parental Genomic Imprinting Memory within Donor Cell-Inherited Nuclear Genome be a Major Hindrance for the Somatic Cell Cloning of Mammals? – A Review

Successful cloning of animals by somatic cell nuclear transfer (SCNT) requires epigenetic transcriptional reprogramming of the differentiated state of the donor cell nucleus to a totipotent embryonic ground state. It means that the donor nuclei must cease its own program of gene expression and restore a particular program of the embryonic genome expression regulation that is necessary for normal development. Transcriptional activity of somatic cell-derived nuclear genome during embryo pre- and postimplantation development as well as foetogenesis is correlated with the frequencies for spatial remodeling of chromatin architecture and reprogramming of cellular epigenetic memory. This former and this latter process include such covalent modifications as demethylation/re-methylation of DNA cytosine residues and acetylation/deacetylation as well as demethylation/re-methylation of lysine residues of nucleosomal core-derived histones H3 and H4. The main cause of low SCNT efficiency in mammals turns out to be an incomplete reprogramming of transcriptional activity for donor cell-descended genes. It has been ascertained that somatic cell nuclei should undergo the wide DNA cytosine residue demethylation changes throughout the early development of cloned embryos to reset their own overall epigenetic and parental genomic imprinting memories that have been established by re-methylation of the nuclear donor cell-inherited genome during specific pathways of somatic and germ cell lineage differentiation. A more extensive understanding of the molecular mechanisms and recognition of determinants for epigenetic transcriptional reprogrammability of somatic cell nuclear genome will be helpful to solve the problems resulting from unsatisfactory SCNT effectiveness and open new possibilities for common application of this technology in transgenic research focused on human biomedicine.

Effects of histone methyltransferase inhibitor chaetocin on histone H3K9 methylation of cultured ovine somatic cells and development of preimplantation cloned embryos

Aberrant hypermethylation of histone H3 lysine 9 (H3K9) is a key barrier to the development of cloned embryos by somatic cell nuclear transfer (SCNT). The objective of this study was to assess the effects of chaetocin, an inhibitor of H3K9 methyltransferase SUV39 H, in regulating the H3K9 methylation in ovine SCNT embryos. Treatment of sheep fetal fibroblast cells with chaetocin specifically decreased the levels of H3K9 di-and trimethylation, and down-regulated the expression of H3K9 methyltransferases, SUV39H1/2 and G9A. Cloned embryos from chaetocin-treated cells could develop to the blastocyst stage at a similar rate to those derived from non-treated cells. However, direct treatment of SCNT or in vitro fertilized embryos with chaetocin impaired the embryonic development. These results suggest that although chaetocin is a potential agent for modulating H3K9 methylation in cells, it may have an adverse effect on the development of embryos.

Overexpression of Tet3 in donor cells enhances goat somatic cell nuclear transfer efficiency

Ten-eleven translocation 3 (TET3) mediates active DNA demethylation of paternal genomes during mouse embryonic development. However, the mechanism of DNA demethylation in goat embryos remains unknown. In addition, aberrant DNA methylation reprogramming prevalently occurs in embryos cloned by somatic cell nuclear transfer (SCNT). In this study, we reported that TET3 is a key factor in DNA demethylation in goat pre-implantation embryos. Knockdown of Tet3 hindered DNA demethylation at the two- to four-cell stage in goat embryos and decreased Nanog expression in blastocysts. Overexpression of Tet3 in somatic cells can initiate DNA demethylation, reduce 5-methylcytosine level, increase 5-hydroxymethylcytosine level and promote the expression of key pluripotency genes. After SCNT, overexpression of Tet3 in donor cells corrected abnormal DNA hypermethylation of cloned embryos and significantly enhanced in vitro and in vivo developmental rate (P < 0.05). We conclude that overexpression of Tet3 in donor cells significantly improves goat SCNT efficiency.

Treatment of donor cells with recombinant KDM4D protein improves preimplantation development of cloned ovine embryos

Incomplete epigenetic reprogramming is one of the major factors affecting the development of embryos cloned by somatic cell nuclear transfer (SCNT). Histone 3 lysine 9 (H3K9) trimethylation has been identified as a key barrier to efficient reprogramming by SCNT. The aim of this study was to explore a method of downregulating H3K9me3 levels in donor cells by using histone lysine demethylase (KDM) protein. When sheep fetal fibroblast cells were treated with recombinant human KDM4D protein (rhKDM4D), the levels of H3K9 trimethylation and dimethylation were both significantly decreased. After SCNT, rhKDM4D-treated donor cells supported significantly higher percentage of cloned embryos developing into blastocysts as compared to non-treated control cells. Moreover, the blastocyst quality was also improved by rhKDM4D treatment of donor cells, as assessed by the total cell number in blastocysts and the expression of developmental genes including SOX2, NANOG and CDX2. These results indicate that treatment of donor cells with recombinant KDM4D protein can downregulate the levels of H3K9 trimethylation and dimethylation and improve the developmental competence of SCNT embryos. This strategy may be convenient to be used in KDM4-assisted SCNT procedure for improving the efficiency of cloning.

DZNep and UNC0642 enhance in vitro developmental competence of cloned pig embryos

Somatic cell nuclear transfer in mammalian cloning suffers from a faulty epigenetic reprogramming, which is believed to cause developmental failures in cloned embryos. Regulating the epigenetic-modifying enzymes can rescue the chromatin of cloned embryos from aberrant epigenetic status, thereby potentially promoting cloning efficiency. In this study, we investigated the effect of two histone methyltransferase inhibitors, namely, DZNep and UNC0642, on the in vitro developmental competence of cloned pig embryos. We found that (1) treatment with 10 nM DZNep or 5 nM UNC0642 for 24 h after activation had the best promoting effect on the development of cloned embryos (blastocyst rate 10.32% vs 18.08% for DZNep, and 10.44% vs 18.14% for UNC0642); (2) 10 nM DZNep and 5 nM UNC0642 significantly decreased the levels of H3K27me3 and H3K9me2, respectively, at the 2-cell, 4-cell and blastocyst stages; (3) the apoptosis level was lower in the treatment groups than in untreated control; and (4) the transcriptional expression of epigenetic genes (EZH2, GLP, G9a, Setdb1, Setdb2, Suv39h1 and Suv39h2) was decreased and pluripotency genes (Nanog, Pou5f1, Sox2 and Bmp4) was increased in treatment groups compared with control. These results indicated that treatment with DZNep and UNC0642 improves the epigenetic reprogramming of cloned embryos, which could render beneficial effect on the embryo quality and aberrant gene expression, and finally improve the developmental competence of cloned pig embryos.

Treating donor cells with 2-PCPA corrects aberrant histone H3K4 dimethylation and improves cloned goat embryo development

Epigenetic modifications extensively occur in mammalian embryonic development and cell differentiation process. They play an essential role in the reprogramming of nuclei during somatic cell nuclear transfer (SCNT) and subsequent in vitro embryonic development. Recently, SCNT embryos have been verified to contain a subnormal level of histone H3K4 dimethylation (H3K4me2) in contrast to in vitro fertilized embryos. This finding suggested that increasing H3K4me2 levels may ameliorate the aberrant development of cloned embryos. In this study, we investigated the influence of treating donor cells with trans-2-Phenylcyclopropylamine (2-PCPA), a specific inhibitor of lysine-specific demethylase 1 (LSD1), on embryogenesis, H3K4me2 level, and gene expression in cloned goat embryos. Treated goat fetal fibroblast cells (GFFs) with 2-PCPA served as donor cells for subsequent SCNT. Results showed that H3K4me2 levels in treated GFFs increased gradually with the increasing 2-PCPA concentration (p < 0.05) and had no obvious influence in cell viability. The 2-PCPA-induced up-regulation of H3K4me2 levels led to G0/G1 cell cycle arrest and the difference was significant at 2μM compared with the control group (p < 0.05). Interestingly, the development rate of goat SCNT embryos in vitro was significantly improved and aberrant H3K4me2 levels were effectively corrected in 2-PCPA-treated SCNT embryos in contrast to that in SCNT control embryos. Moreover, 2-PCPA treatment promoted the mRNA expression of key developmental genes Oct4 and Sox2 (p < 0.05) without affecting the expression levels of imprinted genes IGF2R and H19 in goat SCNT embryos. These results indicated that abnormal H3K4me2 status can be corrected and SCNT embryo development can be promoted through treatment of donor cells with 2-PCPA.

ABBREVIATIONS

SCNT: somatic cell nuclear transfer; H3K4me2: H3K4 dimethylation; 2-PCPA: trans-2-Phenylcyclopropylamine; LSD1: lysine-specific demethylase 1; GFFs: goat fetal fibroblast cells; IVF: in vitro fertilization; iPS: induced pluripotent stem; PBS: phosphate-buffered saline; IVM: in vitro maturation; RNAPII: RNA polymerase II; HMTs: histone methyltransferase.

Piwil2 is reactivated by HPV oncoproteins and initiates cell reprogramming via epigenetic regulation during cervical cancer tumorigenesis

The human papillomavirus (HPV) oncoproteins E6 and E7 are risk factors that are primarily responsible for the initiation and progression of cervical cancer, and they play a key role in immortalization and transformation by reprogramming differentiating host epithelial cells. It is unclear how cervical epithelial cells transform into tumor-initiating cells (TICs). Here, we observed that the germ stem cell protein Piwil2 is expressed in pre-cancerous and malignant lesions of the cervix and cervical cancer cell lines with the exception of the non-HPV-infected C33a cell line. Knockdown of Piwil2 by shRNA led to a marked reduction in proliferation and colony formation, in vivo tumorigenicity, chemo-resistance, and the proportion of cancer stem-like cells. In contrast, Piwil2 overexpression induced malignant transformation of HaCaT cells and the acquisition of tumor-initiating capabilities. Gene-set enrichment analysis revealed embryonic stem cell (ESC) identity, malignant biological behavior, and specifically, activation targets of the cell reprogramming factors c-Myc, Klf4, Nanog, Oct4, and Sox2 in Piwil2-overexpressing HaCaT cells. We further confirmed that E6 and E7 reactivated Piwil2 and that E6 and E7 overexpression resulted in a similar gene-set enrichment pattern as Piwil2 overexpression in HaCaT cells. Moreover, Piwil2 overexpression or E6 and E7 activation induced H3K9 acetylation but reduced H3K9 trimethylation, which contributed to the epigenetic reprogramming and ESC signature maintenance, as predicted previously. Our study demonstrates that Piwil2, reactivated by the HPV oncoproteins E6 and E7, plays an essential role in the transformation of cervical epithelial cells to TICs via epigenetics-based cell reprogramming.

H3K9 demethylase KDM4E is an epigenetic regulator for bovine embryonic development and a defective factor for nuclear reprogramming

Aberrant epigenetic reprogramming often results in developmental defects in somatic cell nuclear transfer (SCNT) embryos during embryonic genome activation (EGA). Bovine eight-cell SCNT embryos exhibit global hypermethylation of histone H3 lysine 9 tri- and di-methylation (H3K9me3/2), but the intrinsic reason for this remains elusive. Here, we provide evidence that two H3K9 demethylase genes, lysine-specific demethylase 4D (KDM4D) and 4E (KDM4E), are related to active H3K9me3/2 demethylation in in vitro fertilized (IVF) embryos and are deficiently expressed in cloned embryos at the time of EGA. Moreover, KDM4E plays a more crucial role in IVF and SCNT embryonic development, and overexpression of KDM4E can restore the global transcriptome, improve blastocyst formation and increase the cloning efficiency of SCNT embryos. Our results thereby indicate that KDM4E can function as a crucial epigenetic regulator of EGA and as an internal defective factor responsible for persistent H3K9me3/2 barriers to SCNT-mediated reprogramming. Furthermore, we show that interactions between RNA and KDM4E are essential for H3K9 demethylation during EGA. These observations advance the understanding of incomplete nuclear reprogramming and are of great importance for transgenic cattle procreation.

Scriptaid improves the reprogramming of donor cells and enhances canine-porcine interspecies embryo development

Histone methylation, histone acetylation, and DNA methylation are the important factors for somatic cell nuclear transfer (SCNT). Histone deacetylase inhibitors (HDACi) and DNA methyltransferase inhibitors (DNMTi) have been used to improve cloning efficiency. In particular, scriptaid, an HDACi, has been shown to improve SCNT efficiency. However, no studies have been performed on canines. Here, we evaluated the effects of scriptaid on histone modification in canine ear fibroblasts (cEFs) and cloned canine embryos derived from cEFs. The early development of cloned canine-porcine interspecies SCNT (iSCNT) embryos was also examined. cEFs were treated with scriptaid (0, 100, 250, 500, 750, and 1000nM) in a medium for 24h. Scriptaid treatment (all concentrations) did not significantly affect cell apoptosis. Treatment with 500nM scriptaid caused a significant increase in the acetylation of H3K9, H3K14, and H4K5. cEFs treated with 500nM scriptaid showed significantly decreased Gcn5, Hat1, Hdac6, and Bcl2 and increased Oct4 and Sox2 expression levels. After SCNT with canine oocytes, H3K14 acetylation was significantly increased in the one- and two-cell cloned embryos from scriptaid-treated cEFs. In iSCNT, the percentage of embryos in the 16-cell stage was significantly higher in the scriptaid-treated group (21.6±2.44%) than in the control (7.5±2.09%). The expression levels of Oct4, Sox2, and Bcl2 were significantly increased in 16-cell iSCNT embryos, whereas that of Hdac6 was decreased. These results demonstrated that scriptaid affected the reprogramming of canine donor and cloned embryos, as well as early embryo development in canine-porcine iSCNT, by regulating reprogramming and apoptotic genes.

Epigenetic Control of Reprogramming and Transdifferentiation by Histone Modifications

Somatic cells can be reprogrammed to pluripotent stem cells or transdifferentiate to another lineage cell type. Much efforts have been made to unravel the epigenetic mechanisms underlying the cell fate conversion. Histone modifications as the major epigenetic regulator are implicated in various aspects of reprogramming and transdifferentiation. Here, we discuss the roles of histone modifications on reprogramming and transdifferentiation and hopefully provide new insights into induction and promotion of the cell fate conversion by modulating histone modifications.

LC3-Dependent Autophagy in Pig 2-Cell Cloned Embryos Could Influence the Degradation of Maternal mRNA and the Regulation of Epigenetic Modification

In this study, the distribution as well as the effect of autophagy on reprogramming in pig cloned embryos were observed immediately after somatic cell nuclear transfer. Results showed that the LC3 was at the highest level in cloned embryos at 2-cell stage, and it decreased with the development from 2-cell stage to blastocyst. Different to cloned embryos, the intensity of LC3 in parthenogenetic activation (PA) embryos was at the highest level at 4-cell stage. A markedly higher level of Bmp15, H1foo, and Dppa3 was shown in cloned embryos at 2-cell stage (p < 0.05 or p < 0.01), but a significantly lower level of LC3, Sox2, and eIF1A was observed at 4-cell stage (p < 0.05), compared with PA embryos. When the efficient interfering by the LC3 siRNA was performed on the cloned embryos (p < 0.01), not only the mRNA level of maternal Cyclin B, Bmp15, Gdf9, c-mos, H1foo, and Dppa3 was increased significantly (p < 0.05), but also the expression of Dnmt1 and Dnmt3b was obviously upregulated (p < 0.05). Although the expression of Sox2 and Oct4 is not changed, the expression of Stat3 decreased significantly (p < 0.05). Furthermore with the treatment of 200 nM rapamycin, the expression of eIF1A and Stat3 was significantly increased at 4-cell stage. In conclusion, the LC3-dependent autophagy mainly occurred in cloned embryos at 2-cell stage, but at 4-cell stage in PA embryos. In addition, the modulation of autophagy could affect genome activation by influencing the degradation of maternal mRNA and regulating the expression of DNA methyltransferase.

Melatonin enhances the developmental competence of porcine somatic cell nuclear transfer embryos by preventing DNA damage induced by oxidative stress

Melatonin has antioxidant and scavenger effects in the cellular antioxidant system. This research investigated the protective effects and underlying mechanisms of melatonin action in porcine somatic cell nuclear transfer (SCNT) embryos. The results suggested that the developmental competence of porcine SCNT embryos was considerably enhanced after melatonin treatment. In addition, melatonin attenuated the increase in reactive oxygen species levels induced by oxidative stress, the decrease in glutathione levels, and the mitochondrial dysfunction. Importantly, melatonin inhibited phospho-histone H2A.X (γH2A.X) expression and comet tail formation, suggesting that γH2A.X prevents oxidative stress-induced DNA damage. The expression of genes involved in homologous recombination and non-homologous end-joining pathways for the repair of double-stranded breaks (DSB) was reduced upon melatonin treatment in porcine SCNT embryos at day 5 of development under oxidative stress condition. These results indicated that melatonin promoted porcine SCNT embryo development by preventing oxidative stress-induced DNA damage via quenching of free radical formation. Our results revealed a previously unrecognized regulatory effect of melatonin in response to oxidative stress and DNA damage. This evidence provides a novel mechanism for the improvement in SCNT embryo development associated with exposure to melatonin.

DOT1L inhibitor improves early development of porcine somatic cell nuclear transfer embryos

Incomplete epigenetic reprogramming of the genome of donor cells causes poor early and full-term developmental efficiency of somatic cell nuclear transfer (SCNT) embryos. Previous research indicate that inhibition of the histone H3 K79 methyltransferase DOT1L, using a selective pharmacological inhibitor EPZ004777 (EPZ), significantly improved reprogramming efficiency during the generation of mouse induced pluripotent stem cells. However, the roles of DOT1L in porcine nuclear transfer-mediated cellular reprogramming are not yet known. Here we showed that DOT1L inhibition via 0.5 nM EPZ treatment for 12 or 24 h significantly enhanced the blastocyst rate of SCNT embryos and dramatically reduced the level of H3K79me2 during SCNT 1-cell embryonic development. Additionally, H3K79me2 level in the EPZ-treated SCNT embryos was similar to that in in vitro fertilized embryos, suggesting that DOT1L-mediated H3K79me2 is a reprogramming barrier to early development of porcine SCNT embryos. qRT-PCR analysis further demonstrated that DOT1L inactivation did not change the expression levels of DOT1L itself but increased the expression levels of POU5F1, LIN28, SOX2, CDX2 and GATA4 associated with pluripotency and early cell differentiation. In conclusion, DOT1L inhibitor improved early developmental efficiency of porcine SCNT embryos probably via inducing the increased expression of genes important for pluripotency and lineage specification.

Reprogramming towards totipotency is greatly facilitated by synergistic effects of small molecules

Animal cloning has been achieved in many species by transplanting differentiated cell nuclei to unfertilized oocytes. However, the low efficiencies of cloning have remained an unresolved issue. Here we find that the combination of two small molecules, trichostatin A (TSA) and vitamin C (VC), under culture condition with bovine serum albumin deionized by ion-exchange resins, dramatically improves the cloning efficiency in mice and 15% of cloned embryos develop to term by means of somatic cell nuclear transfer (SCNT). The improvement was not observed by adding the non-treated, rather than deionized, bovine serum. RNA-seq analyses of SCNT embryos at the two-cell stage revealed that the treatment with TSA and VC resulted in the upregulated expression of previously identified reprogramming-resistant genes. Moreover, the expression of early-embryo-specific retroelements was upregulated by the TSA and VC treatment. The enhanced gene expression was relevant to the VC-mediated reduction of histone H3 lysine 9 methylation in SCNT embryos. Our study thus shows a simply applicable method to greatly improve mouse cloning efficiency, and furthers our understanding of how somatic nuclei acquire totipotency.

Summary: The optimized culture condition with small molecules is sufficient to allow highly efficient mouse cloning by removing epigenetic barriers to reprogramming.

TSA and BIX-01294 Induced Normal DNA and Histone Methylation and Increased Protein Expression in Porcine Somatic Cell Nuclear Transfer Embryos

The poor efficiency of animal cloning is mainly attributed to the defects in epigenetic reprogramming of donor cells' chromatins during early embryonic development. Previous studies indicated that inhibition of histone deacetylases or methyltransferase, such as G9A, using Trichostatin A (TSA) or BIX-01294 significantly enhanced the developmental efficiency of porcine somatic cell nuclear transfer (SCNT) embryos. However, potential mechanisms underlying the improved early developmental competence of SCNT embryos exposed to TSA and BIX-01294 are largely unclear. Here we found that 50 nM TSA or 1.0 μM BIX-01294 treatment alone for 24 h significantly elevated the blastocyst rate (P < 0.05), while further improvement was not observed under combined treatment condition. Furthermore, co-treatment or TSA treatment alone significantly reduced H3K9me2 level at the 4-cell stage, which is comparable with that in in vivo and in vitro fertilized counterparts. However, only co-treatment significantly decreased the levels of 5mC and H3K9me2 in trophectoderm lineage and subsequently increased the expression of OCT4 and CDX2 associated with ICM and TE lineage differentiation. Altogether, these results demonstrate that co-treatment of TSA and BIX-01294 enhances the early developmental competence of porcine SCNT embryos via improvements in epigenetic status and protein expression.

Inhibition of Histone H3K9 Methylation by BIX-01294 Promotes Stress-Induced Microspore Totipotency and Enhances Embryogenesis Initiation

Microspore embryogenesis is a process of cell reprogramming, totipotency acquisition and embryogenesis initiation, induced in vitro by stress treatments and widely used in plant breeding for rapid production of doubled-haploids, but its regulating mechanisms are still largely unknown. Increasing evidence has revealed epigenetic reprogramming during microspore embryogenesis, through DNA methylation, but less is known about the involvement of histone modifications. In this study, we have analyzed the dynamics and possible role of histone H3K9 methylation, a major repressive modification, as well as the effects on microspore embryogenesis initiation of BIX-01294, an inhibitor of histone methylation, tested for the first time in plants, in Brassica napus and Hordeum vulgare. Results revealed that microspore reprogramming and initiation of embryogenesis involved a low level of H3K9 methylation. With the progression of embryogenesis, methylation of H3K9 increased, correlating with gene expression profiles of BnHKMT SUVR4-like and BnLSD1-like (writer and eraser enzymes of H3K9me2). At early stages, BIX-01294 promoted cell reprogramming, totipotency and embryogenesis induction, while diminishing bulk H3K9 methylation. DNA methylation was also reduced by short-term BIX-01294 treatment. By contrast, long BIX-01294 treatments hindered embryogenesis progression, indicating that H3K9 methylation is required for embryo differentiation. These findings open up new possibilities to enhance microspore embryogenesis efficiency in recalcitrant species through pharmacological modulation of histone methylation by using BIX-01294.