Increased blastocyst formation of cloned porcine embryos produced with donor cells pre-treated with Xenopus egg extract and/or digitonin

Effects of Cellular Extract on Epigenetic Reprogramming

Functional reprogramming of a differentiated cell toward pluripotent cell may have long-term applications in numerous aspects, especially in regenerative medicine. Evidences accumulating from recent studies suggest that cellular extracts from stem cells or pluripotent cells can induce epigenetic reprogramming and facilitate pluripotency in otherwise highly differentiated cell types. Epigenetic reprogramming using cellular extracts has gained increasing attention and applied to recognize the functional factors, acquire the target cell types, and explain the mechanism of reprogramming. Now, more and more researches have proved that cellular extract treatment is an important strategy of cellular reprogramming. Thus, this review mainly focused on the progresses and potential mechanisms in epigenetic reprogramming using cellular extracts.

Cloning: A Sleeping Beauty Awaiting the Kiss?

The first 20 years of somatic cell nuclear transfer can hardly be described as a success story. Controversially, many factors leading to the fiasco are not intrinsic features of the technique itself. Misunderstandings and baseless accusations alongside with unsupported fears and administrative barriers hampered cloners to overcome the initial challenging period with obvious difficulties that are common features of a radically new approach. In spite of some promising results of mostly sporadic and small-scale experiments, the future of cloning is still uncertain. On the other hand, a reincarnation, just like the idea of electric cars, may result in many benefits in various areas of science and economy. One can only hope that-in contrast to electric cars-the ongoing paralyzed phase will not last for 100 years, and breakthroughs achieved in some promising areas will provide enough evidence to intensify research and large-scale application of cloning in the next decade.

Nuclear import of Xenopus egg extract components into cultured cells for reprogramming purposes: a case study on goldfish fin cells

Reprogramming of cultured cells using Xenopus egg extract involves controlling four major steps: plasma membrane permeabilization, egg factors import into the nucleus, membrane resealing, and cell proliferation. Using propidium iodide to assess plasma membrane permeability, we established that 90% of the cultured fin cells were permeabilized by digitonin without any cell losses. We showed that egg extract at metaphase II stage was essential to maintain nuclear import function in the permeabilized cells, as assessed with a fusion GFP protein carrying the nuclear import signal NLS. Moreover, the Xenopus-egg-specific Lamin B3 was detected in 87% of the cell nuclei, suggesting that other egg extract reprogramming factors of similar size could successfully enter the nucleus. Lamin B3 labelling was maintained in most cells recovered 24 h after membrane resealing with calcium, and cells successfully resumed cell cycle in culture. In contrast, permeabilized cells that were not treated with egg extract failed to proliferate in culture and died, implying that egg extract provided factor essential to the survival of those cells. To conclude, fish fin cells were successfully primed for treatment with reprogramming factors, and egg extract was shown to play a major role in their survival and recovery after permeabilization.

Various nuclear reprogramming systems using egg and oocyte materials

Maternal factors stored in eggs and oocytes are necessary for reprogramming sperm for embryonic development. This reprogramming activity of maternal factors also works towards somatic cells, including terminally differentiated cells. Several different experimental systems utilizing egg and oocyte materials have been applied to study nuclear reprogramming by maternal factors. Among these systems, the most widely used is the transfer of a somatic cell nucleus to an oocyte arrested at the metaphase II stage, leading to the production of a cloned animal. Nuclear transfer to an unfertilized oocyte thus provides a unique opportunity to examine reprogramming processes involved in acquiring totipotency. Other experimental systems are also available to study maternal reprogramming, such as nuclear transfer to Xenopus laevis oocytes at the germinal vesicle stage, treatment with extracts obtained from eggs or oocytes, and induced pluripotency with overexpressed maternal factors. Each system can be used for answering different types of scientific questions. This review describes currently available reprogramming systems using egg and oocyte materials and discusses how we can deepen our understanding of reprogramming mechanisms by taking advantage of these various experimental systems.

Apolipoprotein E Deficiency Increases Remnant Lipoproteins and Accelerates Progressive Atherosclerosis, But Not Xanthoma Formation, in Gene-Modified Minipigs

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APOE-deficient Yucatan minipigs were created by recombinant adeno-associated virus mediated gene targeting in porcine fibroblasts followed by somatic cell nuclear transfer.

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APOE^−/− minipigs displayed increased plasma cholesterol and accumulation of APOB48-containing chylomicron remnants on low fat-diet, which was significantly accentuated upon feeding a high-fat, high-cholesterol diet.

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APOE^−/− minipigs showed accelerated progressive atherosclerosis but not xanthoma formation indicating that remnant lipoproteinemia does not induce early lesions but is atherogenic in pre-existing atherosclerosis.

Deficiency of apolipoprotein E (APOE) causes familial dysbetalipoproteinemia in humans resulting in a higher risk of atherosclerotic disease. In mice, APOE deficiency results in a severe atherosclerosis phenotype, but it is unknown to what extent this is unique to mice. In this study, APOE was targeted in Yucatan minipigs. APOE^−/− minipigs displayed increased plasma cholesterol and accumulation of apolipoprotein B-48–containing chylomicron remnants on low-fat diet, which was significantly accentuated upon feeding a high-fat, high-cholesterol diet. APOE^−/− minipigs displayed accelerated progressive atherosclerosis but not xanthoma formation. This indicates that remnant lipoproteinemia does not induce early lesions but is atherogenic in pre-existing atherosclerosis.

Exposure of Somatic Cells to Cytoplasm Extracts of Porcine Oocytes Induces Stem Cell-Like Colony Formation and Alters Expression of Pluripotency and Chromatin-Modifying Genes

Cell permeabilization followed by exposure to cytoplasmic extracts of oocytes has been proposed as an alternative to transduction of transcription factors for inducing pluripotency in cultured somatic cells. The main goal in this study was to investigate the effect of treating porcine fibroblast cells with cytoplasmic extracts of GV-stage oocyte (OEx) followed by inhibition of histone deacetylases with Scriptaid (Scrip) on the formation of stem cell-like colonies and expression of genes encoding pluripotency and chromatin-modifying enzymes. Stem cell-like colonies start developing ∼2 weeks after treatment in cells exposed to OEx or OEx + Scrip. The number of cell colonies at the first day of appearance and 48 hours later was also similar between OEx and OEx + Scrip treatments. Transcripts for Nanog, Rex1, and c-Myc genes were detected in most cell samples that were analyzed on different days after OEx treatment. However, Sox2 transcripts were not detected and only a small proportion of samples had detectable levels of Oct4 mRNA after OEx treatment. A similar pattern of transcripts for pluripotency genes was observed in cells treated with OEx alone or OEx + Scrip. Transcript levels for Dnmt1 and Ezh2 were reduced at Day 3 after treatment in cells exposed to OEx. These findings revealed that: (a) exposure to OEx can induce a partial reprogramming of fibroblast cells toward pluripotency, characterized by colony formation and activation of pluripotency genes; and (b) inhibition of histone deacetylases does not improve the reprogramming effect of OEx treatment.

Long-term effect on in vitro cloning efficiency after treatment of somatic cells with Xenopus egg extract in the pig

In somatic cell nuclear transfer (SCNT), donor cell reprogramming is considered as a biologically important and vulnerable event. Various donor cell pre-treatments with Xenopus egg extracts can promote reprogramming. Here we investigated if the reprogramming effect of one treatment with Xenopus egg extract on donor cells was maintained for several cell passages. The extract treatment resulted in increased cell-colony formation from early passages in treated porcine fibroblasts (ExTES), and increased development of cloned embryos. Partial dedifferentiation was observed in ExTES cells, shown as a tendency towards upregulation of NANOG, c-MYC and KLF-4 and downregulation of DESMIM compared with ExTES at Passage 2. Compared with our routine SCNT, continuously increased development of cloned embryos was observed in the ExTES group, and ExTES cloned blastocysts displayed hypermethylated DNA patterns and hypermethylation of H3K4me3 and H3K27me3 in ICM compared with TE. All seven recipients became pregnant after transferral of ExTES cloned embryos and gave birth to 7-22 piglets per litter (average 12). In conclusion, our results demonstrate that one treatment of porcine fibroblasts with Xenopus egg extract can result in long-term increased ability of the cells to promote their in vitro function in subsequent SCNT. Finally these cells can also result in successful development of cloned embryos to term.

Cell-free extract from porcine induced pluripotent stem cells can affect porcine somatic cell nuclear reprogramming

Pretreatment of somatic cells with undifferentiated cell extracts, such as embryonic stem cells and mammalian oocytes, is an attractive alternative method for reprogramming control. The properties of induced pluripotent stem cells (iPSCs) are similar to those of embryonic stem cells; however, no studies have reported somatic cell nuclear reprogramming using iPSC extracts. Therefore, this study aimed to evaluate the effects of porcine iPSC extracts treatment on porcine ear fibroblasts and early development of porcine cloned embryos produced from porcine ear skin fibroblasts pretreated with the porcine iPSC extracts. The Chariot(TM) reagent system was used to deliver the iPSC extracts into cultured porcine ear skin fibroblasts. The iPSC extracts-treated cells (iPSC-treated cells) were cultured for 3 days and used for analyzing histone modification and somatic cell nuclear transfer. Compared to the results for nontreated cells, the trimethylation status of histone H3 lysine residue 9 (H3K9) in the iPSC-treated cells significantly decreased. The expression of Jmjd2b, the H3K9 trimethylation-specific demethylase gene, significantly increased in the iPSC-treated cells; conversely, the expression of the proapoptotic genes, Bax and p53, significantly decreased. When the iPSC-treated cells were transferred into enucleated porcine oocytes, no differences were observed in blastocyst development and total cell number in blastocysts compared with the results for control cells. However, H3K9 trimethylation of pronuclear-stage-cloned embryos significantly decreased in the iPSC-treated cells. Additionally, Bax and p53 gene expression in the blastocysts was significantly lower in iPSC-treated cells than in control cells. To our knowledge, this study is the first to show that an extracts of porcine iPSCs can affect histone modification and gene expression in porcine ear skin fibroblasts and cloned embryos.

Early embryonic development, assisted reproductive technologies, and pluripotent stem cell biology in domestic mammals

Over many decades assisted reproductive technologies, including artificial insemination, embryo transfer, in vitro production (IVP) of embryos, cloning by somatic cell nuclear transfer (SCNT), and stem cell culture, have been developed with the aim of refining breeding strategies for improved production and health in animal husbandry. More recently, biomedical applications of these technologies, in particular, SCNT and stem cell culture, have been pursued in domestic mammals in order to create models for human disease and therapy. The following review focuses on presenting important aspects of pre-implantation development in cattle, pigs, horses, and dogs. Biological aspects and impact of assisted reproductive technologies including IVP, SCNT, and culture of pluripotent stem cells are also addressed.

Early development of the porcine embryo: the importance of cell signalling in development of pluripotent cell lines

Understanding the cell signalling events that govern cell renewal in porcine pluripotent cells may help improve culture conditions and allow for establishment of bona fide porcine embryonic stem cells (pESC) and stable porcine induced pluripotent stem cells (piPSC). This review investigates cell signalling in the porcine preimplantation embryo containing either the inner cell mass or epiblast, with particular emphasis on fibroblast growth factor, SMAD, WNT and Janus tyrosine kinases/signal transducers and activators of transcription signalling. It is clear that key differences exist in the cell signalling events that govern pluripotency in this species compared with similar embryonic stages in mouse and human. The fact that bona fide pESC have still not been produced and that piPSC cannot survive in culture following the silencing or downregulation of the reprogramming transgenes suggest that culture conditions are not optimal. Unravelling the factor/s that regulate pluripotency in porcine embryos will pave the way for future establishment of stable pluripotent stem cell lines.

Xenopus egg extract treatment reduced global DNA methylation of donor cells and enhanced somatic cell nuclear transfer embryo development in pigs

The efficiency to produce offspring by somatic cell nuclear transfer (SCNT) is low. It has been showed that treatment of donor cells with Xenopus oocyte extract increased live births in ovine and handmade cloned embryo development in pigs. Scriptaid treatment after oocyte activation is another approach to improve SCNT efficiency. The present study was carried out to investigate (a) the effects of treatment of donor cells with Xenopus egg extract on donor cell DNA methylation at days 0 and 4 with two digitonin permeabilization concentrations (10 and 15 μg/mL), (b) the effects of treatment of donor cells with Xenopus egg extract on early development of cloned embryos, and (c) the effects of combined treatments, treating donor cells with extract before nuclear transfer and treatment of cloned embryos with scriptaid after oocyte activation, on embryo development. Compared to the control, a decrease of DNA methylation in donor cells was observed at 2.5 h after extract treatment. However, this effect was not observed after the cells were cultured for four more days. More embryos developed into blastocysts in the Xenopus egg extract-treated group than in the control (13.4±1.9% vs. 9.1±1.9%, p=0.01). Furthermore, scriptaid treatment of cloned embryos further increased the frequency of development to blastocyst, compared to the control reconstructed with the same extract-treated cells (22.5±0.9% vs. 15.3±0.9%, p<0.01). In addition, egg extract treatments increased the cell number in the blastocysts. This study demonstrated that Xenopus egg extract treatment reduced donor cell DNA methylation and enhanced the SCNT embryo development. Moreover, the combined treatments of donor cells with egg extract before nuclear transfer and of cloned embryos with scriptaid could improve cloned embryo development additively.