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

Abstract

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.

Oviduct epithelial cells‐derived extracellular vesicles improve preimplantation developmental competence of in vitro produced porcine parthenogenetic and cloned embryos

“…Pluripotency transcriptional factors (POU5F1, NANOG, and SOX2) were correlated with low DNA methylation levels in epigenetic regulation. DNA methylation and histone modification suggest a vital role for SCNT embryos (Simmet et al, 2020; Wang et al, 2020). Studies have shown that miRNAs are identified in oviductal EVs (oEVs), and potential target genes are involved in embryo development (Almiñana & Bauersachs, 2019).…”

A New Toolbox in Experimental Embryology—Alternative Model Organisms for Studying Preimplantation Development

“…X-inactivation in mammals is still a topic with open questions and species-specific differences were reported [ 196 , 197 ]. In cloned embryos, abnormal development in both sexes was shown and a connection to variations in X-inactivation was established (reviewed in [ 97 ]). These differences between sexes and the effect of in vitro culture on kinetics and epigenetic reprogramming must be considered.…”

“…Problems occurring when conducting SCNT are micromanipulation trauma, oocyte incompetence, in vitro culture-induced anomalies and failed epigenetic reprogramming of the transferred nucleus (reviewed in [ 96 ]). As a result, physiological development is considered to be impaired as abnormal epigenetic profiles and gene expression may occur (reviewed in [ 97 ]). After transfer of bovine SCNT embryos to recipients, placental failure has frequently been observed, likely due to abnormal embryo-maternal communication during peri-implantation [ 98 , 99 ], giving a possible explanation for the high rate of pregnancy failures.…”

“…Cao, et al [ 102 ] described a delayed zygotic genome activation (ZGA) and altered gene expression patterns in pig embryos produced by SCNT. Despite its limitations, SCNT has tremendous advantages, particularly for the generation of genetically engineered/genome edited large animal models, and further progress in modulating the epigenome could improve nuclear reprogramming (reviewed in [ 97 ]).…”

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

“…Although many transgenic pigs have been created, the cloning efficiency remains extremely low due to a low rate of full-term development, and high rates of pregnancy loss and fetal abnormalities (Wilmut et al, 2002;Whitworth and Prather, 2010;Chavatte-Palmer et al, 2012). Increasing evidence suggests that incomplete epigenetic reprogramming of the donor cell (in terms of DNA methylation and histone methylation/acetylation) causes low cloning efficiency (Dean et al, 2001;Matoba and Zhang, 2018;Simmet et al, 2020;Wang et al, 2020).…”