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

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.

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.

Developmental Competence and Epigenetic Profile of Porcine Embryos Produced by Two Different Cloning Methods

The "Dolly" based cloning (classical nuclear transfer, [CNT]) and the handmade cloning (HMC) are methods that are nowadays routinely used for somatic cloning of large domestic species. Both cloning protocols share several similarities, but differ with regard to the required in vitro culture, which in turn results in different time intervals until embryo transfer. It is not yet known whether the differences between cloned embryos from the two protocols are due to the cloning methods themselves or the in vitro culture, as some studies have shown detrimental effects of in vitro culture on conventionally produced embryos. The goal of this study was to unravel putative differences between two cloning methods, with regard to developmental competence, expression profile of a panel of developmentally important genes and epigenetic profile of porcine cloned embryos produced by either CNT or HMC, either with (D5 or D6) or without (D0) in vitro culture. Embryos cloned by these two methods had a similar morphological appearance on D0, but displayed different cleavage rates and different quality of blastocysts, with HMC embryos showing higher blastocyst rates (HMC vs. CNT: 35% vs. 10%, p < 0.05) and cell numbers per blastocyst (HMC vs. CNT: 31 vs. 23 on D5 and 42 vs. 18 on D6, p < 0.05) compared to CNT embryos. With regard to histone acetylation and gene expression, CNT and HMC derived cloned embryos were similar on D0, but differed on D6. In conclusion, both cloning methods and the in vitro culture may affect porcine embryo development and epigenetic profile. The two cloning methods essentially produce embryos of similar quality on D0 and after 5 days in vitro culture, but thereafter both histone acetylation and gene expression differ between the two types of cloned embryos.

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.

Increasing efficiency in production of cloned piglets

The low efficiency in obtaining piglets after production of cloned embryos was challenged in two steps-first by performing in vitro culture for 5-6 days after cloning to obtain later-stage embryos for more precise selection for transfer, and second by reducing the number of embryos transferred per recipient sow. The data set consisted of combined results from a 4-year period where cloning was performed to produce piglets that were transgenic for important human diseases. For this, different transgenes and cell types were used, and the cloning work was performed by several persons using oocytes from different pig breeds, but following a standardized and optimized protocol. Results showed that in vitro culture is possible with a relatively stable rate of transferable embryos around 41% and a pregnancy rate around 90%. Furthermore, a reduction from around 80 embryos to 40 embryos transferred per recipient was possible without changing the efficiency of around 14% (piglets born out of embryos transferred). It was concluded that this approach can increase the efficiency in obtaining piglets by means of in vitro culture and selection of high-quality embryos with subsequent transfer into more recipients. Such changes can also reduce the need for personnel, time, and material when working with this technology.

Cellular extract facilitates nuclear reprogramming by altering DNA methylation and pluripotency gene expression

The functional reprogramming of a differentiated cell to a pluripotent state presents potential beneficial applications in disease mechanisms and regenerative medicine. Epigenetic modifications enable differentiated cells to perpetuate molecular memory to retain their identity. Therefore, the aim of this study was to investigate the reprogramming modification of yak fibroblast cells that were permeabilized and incubated in the extracts of mesenchymal stem cells derived from mice adipose tissue [adipose-derived stem cells (ADSCs)]. According to the results, the treatment of ADSC extracts promoted colony formation. Moreover, pluripotent gene expression was associated with the loss of repressive histone modifications and increased global demethylation. The genes Col1a1 and Col1a2, which are typically found in differentiated cells only, demonstrated decreased expression and increased methylation in the 5'-flanking regulatory regions. Moreover, yak fibroblast cells that were exposed to ADSC extracts resulted in significantly different eight-cell and blastocyst formation rates of cloned embryos compared with their untreated counterparts. This investigation provides the first evidence that nuclear reprogramming of yak fibroblast cells is modified after the ADSC extract treatment. This research also presents a methodology for studying the dedifferentiation of somatic cells that can potentially lead to an efficient way of reprogramming somatic cells toward a pluripotent state without genetic alteration.