Effect of supplemetation of Zebularine and Scriptaid on efficiency of in vitro developmental competence of ovine somatic cell nuclear transferred embryos

Reproduction of Sheep through Nuclear Transfer of Somatic Cells: A Bibliometric Approach

Somatic cell nuclear transfer (SCNT) is a reproductive biotechnology with great potential in the reproduction of different species of zootechnical interest, including sheep. This study aimed to carry out a bibliometric analysis of scientific papers published on the application of SCNT in sheep reproduction during the period 1997-2023. The search involved the Science Citation Index Expanded and Social Sciences Citation Index databases of the main collection of the Web of Sciences with different descriptors. A total of 124 scientific papers were analyzed for different bibliometric indicators using the VOSviewer software. Since 2001, the number of SCNT-related papers that have been published concerning sheep reproduction has increased and it has fluctuated in ensuing years. The main authors, research groups, institutions, countries, papers, and journals with the highest number of papers related to the application of SCNT in sheep reproduction were identified, as well as the topics that address the research papers according to the terms: somatic cell, embryo, oocyte, gene expression, SCNT, and sheep.

Global DNA methylation, DNA methyltransferase and stress-related gene expression in ovine oocytes and embryos after exposure to metabolic stressors

DNA methylation, considered the most prominent epigenetic mark was important for the gene regulation in embryonic development. The present study aimed at evaluating the effects of metabolic stressors [Non-esterified fatty acid (NEFA), β-hydroxy-butyric acid (BHB), ammonia and urea] exposure during the in vitro ovine oocyte maturation, global DNA methylation, DNA methyltransferase and stress-related gene expression. Colorimetric analysis of global DNA methylation and the expression of the DNA methyltransferase genes (DNMT1, DNMT3A, and DNMT3B) were assessed in the matured oocytes, 2-cell embryos and blastocysts produced in vitro from oocytes exposed with the metabolic stressors during 24 h of the in vitro maturation (IVM). Further, the mRNA expression of the stress-related genes (SOD1, SOD2) in the matured oocytes, 2-cell embryos and blastocysts produced was assessed. Significant difference in global DNA methylation levels between all the treatments tested was observed when compared with control in oocytes, two-cell embryos and blastocysts. Elevated concentration of metabolic stressors resulted in increased expressions of several stress-related genes, i.e., SOD1, SOD2 and in mRNA expression of DNA methyltransferase genes. The present study is the first to report that the DNA methylation was sensitive to the effects of the metabolic stressors in ovine oocytes/embryos. The aberrant expressions of genes during oocyte development targeted in the present study can provide evidence for the early embryo developmental arrest and blastocysts quality. These results highlighted the sensitivity of the early embryogenesis and more precisely of the reprogramming period to metabolites challenges, in a realistic situation of elevated concentration of metabolic stressors.

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.

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.

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.

Enhancement of epigenetic reprogramming status of porcine cloned embryos with zebularine, a DNA methyltransferase inhibitor

Aberrant epigenetic reprogramming is known to be a major cause of inefficient somatic cell nuclear transfer (SCNT) in pigs, and use of epigenetic modification agents, such as DNA methyltransferase inhibitors (DNMTis), is a promising approach for enhancing SCNT efficacy. Here, we attempted to find the optimal condition of zebularine (Zb), a DNMTi, treatment on porcine SCNT embryos during in vitro culture (IVC). As results, treatment with 5 nM Zb for 24 hr showed the highest rate of embryo development to blastocyst compared to other groups (p < .05). Also, the relative intensities of global DNA methylation levels of anti-5-methylcytosine in pseudo-pronuclear (PNC), 2-cell and 4-cell stages were significantly lower in the Zb-treated group (p < .05), however, changes in methylation levels of centromeric satellite repeat were noted only in PNC and blastocyst stages. In addition, significant positive alterations in the relative expression of genes related to pluripotency (OCT4 and SOX2), histone acetylation (HAT1, HDAC1, HDAC2, and HDAC3) and DNA methylation (DNMT1 and DNMT3a) were observed compared to the control (p < .05). In conclusion, we found that Zb could modify DNA methylation levels in the early stages of porcine SCNT embryos and promote their developmental competence.