Effect of POU5F1 Expression Level in Clonal Subpopulations of Bovine Fibroblasts Used as Nuclear Donors for Somatic Cell Nuclear Transfer

Characterization of DNA methylation profile of the entire CpG island spanning the 5' untranslated region to intron 1 of the Oct4/POU5F1 gene in bovine gametes, embryos, and somatic cells

Stem cells are undifferentiated cells that exhibit a bivalent chromatin state that determines their fate. These cells have potential applications in human and animal health and livestock production. Somatic cell nuclear transfer or cloning is currently being used to produce genetically edited animals. A highly differentiated genome is the main obstacle to correcting epigenetic reprogramming by enucleated oocytes during cloning. Activation of pluripotency genes in the somatic genome is a promising strategy to contribute to more efficient epigenetic reprogramming, improving this technique. Recently, epigenome editing has emerged as a new generation of clustered regularly interspaced short palindromic repeats-clustered regularly interspaced short palindromic repeats-associated protein 9 technology with the aim of modifying the cellular epigenome to turn genes on or off without modifying DNA. Here, we characterize the DNA methylation profile of the CpG island spanning the 5' untranslated region to intron 1 of the bovine octamer-binding transcription factor (Oct4) gene in gametes, embryos, and fibroblasts. DNA methylation patterns were categorized into three levels: low (0%-20%), moderate (21%-50%), and high (51%-100%). Sperm and embryos showed a hypomethylation pattern, whereas oocytes exhibited a hypo- to moderate methylation pattern. Fetal and adult skin fibroblasts were hypomethylated and moderately methylated, respectively. These results are essential for future studies aimed at manipulating the expression of Oct4. Thus, epigenome editing can be used to turn on the Oct4 in somatic cells to generate induced pluripotent stem cells. This strategy could potentially convert a fully differentiated cell into a cell with certain degree of pluripotency, facilitating nuclear reprogramming by the enucleated oocyte and improving cloning success rates.

Exogenous Expression of pou5f3 Facilitates the Development of Somatic Cell Nuclear Transfer Embryos in Zebrafish at the Early Stage

Enucleated oocytes can reprogram differentiated nuclei to totipotency after somatic cell nuclear transfer (SCNT), which is valuable in understanding nuclear reprogramming and generating genetically modified animals. To date, reprogramming efficiency is low and the development of SCNT embryos is not going as well as anticipated. To further disclose the reprogramming mechanisms during SCNT zebrafish embryo development, we examined the expression patterns of transcription regulation factors and regulated them by mRNA and morpholino microinjection. In this study, we show that stem cell-related transcription factors are downregulated in zebrafish SCNT embryos at the blastula stage. Exogenous expression of pou5f3 at the single-cell stage improves SCNT embryo development from the blastula to the gastrula stage. We also found that exogenous expression of klf4 or sox2 decreases SCNT embryo development from the blastula to the gastrula stage, while expression of nanog is necessary for the development of SCNT embryos. Our results conclude that zebrafish pou5f3 facilitates the development of SCNT embryos from the blastula to gastrula stage.

Catalytic inhibition of H3K9me2 writers disturbs epigenetic marks during bovine nuclear reprogramming

Orchestrated events, including extensive changes in epigenetic marks, allow a somatic nucleus to become totipotent after transfer into an oocyte, a process termed nuclear reprogramming. Recently, several strategies have been applied in order to improve reprogramming efficiency, mainly focused on removing repressive epigenetic marks such as histone methylation from the somatic nucleus. Herein we used the specific and non-toxic chemical probe UNC0638 to inhibit the catalytic activity of the histone methyltransferases EHMT1 and EHMT2. Either the donor cell (before reconstruction) or the early embryo was exposed to the probe to assess its effect on developmental rates and epigenetic marks. First, we showed that the treatment of bovine fibroblasts with UNC0638 did mitigate the levels of H3K9me2. Moreover, H3K9me2 levels were decreased in cloned embryos regardless of treating either donor cells or early embryos with UNC0638. Additional epigenetic marks such as H3K9me3, 5mC, and 5hmC were also affected by the UNC0638 treatment. Therefore, the use of UNC0638 did diminish the levels of H3K9me2 and H3K9me3 in SCNT-derived blastocysts, but this was unable to improve their preimplantation development. These results indicate that the specific reduction of H3K9me2 by inhibiting EHMT1/2 during nuclear reprogramming impacts the levels of H3K9me3, 5mC, and 5hmC in preimplantation bovine embryos.

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.