Tetraploid Embryonic Stem Cells Maintain Pluripotency and Differentiation Potency into Three Germ Layers

Mouse embryonic stem cells maintain differentiation potency into somatic lineage despite alternation of ploidy

Vertebrates, including mammals, are considered to have evolved by whole genome duplications. Although some fish have been reported to be polyploids that have undergone additional genome duplication, there have been no reports of polyploid mammals due to abnormal development after implantation. Furthermore, as the number of physiologically existing tetraploid somatic cells is small, details of the functions of these ploidy-altered cells are not fully understood. In this present study, we aimed to clarify the details of the differentiation potency of tetraploids using tetraploid embryonic stem cells. To clarify the differentiation potency, we used mouse tetraploid embryonic stem cells derived from tetraploid embryos. We presented tetraploid embryonic stem cells differentiated into neural and osteocyte lineage in vitro and tetraploid cells that contributed to various tissues of chimeric embryos ubiquitously in vivo. These results revealed that mouse embryonic stem cells maintain differentiation potency after altering the ploidy. Our results provide an important basis for the differentiation dynamics of germ layers in mammalian polyploid embryogenesis.

Establishment of a novel method for the production of chimeric mouse embryos using water-in-oil droplets

Production of chimeric animals is often a necessity for the generation of genetically modified animals and has gained popularity in recent years in regenerative medicine for the reconstruction of xenogeneic organs. Aggregation and injection methods are generally used to produce chimeric mice. In the aggregation method, the chimeras are produced by co-culturing embryos and stem cells, and keeping them physically adhered, although it may not be an assured method for producing chimeric embryos. In the injection method, the chimeras are produced by injecting stem cells into the zona pellucida using microcapillaries; however, this technique requires a high degree of skill. This study aimed to establish a novel method for producing chimeric embryos via water-in-oil droplets that differs from conventional methods. In this study, embryonic stem cells and embryos were successfully isolated in the droplets, and the emergence of chimeric embryos was confirmed by co-culture for 6 h. Using this method, the control and operability of stem cell numbers could be regulated, and reproducibility and quantification were improved during the production of chimeric embryos. In addition to the conventional methods for producing chimeric embryos, the novel method described here could be employed for the efficient production of chimeric animals.

Hyper-polyploid embryos survive after implantation in mice

Polyploids generated by natural whole genome duplication have served as a dynamic force in vertebrate evolution. As evidence for evolution, polyploid organisms exist generally, however there have been no reports of polyploid organisms in mammals. In mice, polyploid embryos under normal culture conditions normally develop to the blastocyst stage. Nevertheless, most tetraploid embryos degenerate after implantation, indicating that whole genome duplication produces harmful effects on normal development in mice. Most previous research on polyploidy has mainly focused on tetraploid embryos. Analysis of various ploidy outcomes is important to comprehend the effects of polyploidization on embryo development. The purpose of this present study was to discover the extent of the polyploidization effect on implantation and development in post-implantation embryos. This paper describes for the first time an octaploid embryo implanted in mice despite hyper-polyploidization, and indicates that these mammalian embryos have the ability to implant, and even develop, despite the harmfulness of extreme whole genome duplication.

Induction of pluripotency in mammalian fibroblasts by cell fusion with mouse embryonic stem cells

BACKGROUND

Cell fusion is a phenomenon that is observed in various tissues in vivo, resulting in acquisition of physiological functions such as liver regeneration. Fused cells such as hybridomas have also been produced artificially in vitro. Furthermore, it has been reported that cellular reprogramming can be induced by cell fusion with stem cells.

METHODS

Fused cells between mammalian fibroblasts and mouse embryonic stem cells were produced by electrofusion methods. The phenotypes of each cell lines were analyzed after purifying the fused cells.

RESULTS

Colonies which are morphologically similar to mouse embryonic stem cells were observed in fused cells of rabbit, bovine, and zebra fibroblasts. RT-PCR analysis revealed that specific pluripotent marker genes that were never expressed in each mammalian fibroblast were strongly induced in the fused cells, which indicated that fusion with mouse embryonic stem cells can trigger reprogramming and acquisition of pluripotency in various mammalian somatic cells.

CONCLUSIONS

Our results can help elucidate the mechanism of pluripotency maintenance and the establishment of highly reprogrammed pluripotent stem cells in various mammalian species.

Paraffin-embedded vertical sections of mouse embryonic stem cells

Cultured cells are generally observed through the bottom of dishes or flasks using an inverted microscope. Two-dimensional and horizontal observation is insufficient for histological analysis of several cell lines, such as embryonic stem cells or cancer cells, because they form three-dimensional colonies. In the present study, we aimed to establish a more informative method for analysis of such stereoscopic cultured cells. We cultured mouse embryonic stem cells using a temperature-sensitive culture dish, embedded these cells in paraffin, and successfully observed vertical sections of embryonic stem cells. This vertical analysis of the stereoscopic colony emphasized structural features such as the dome shape of naïve pluripotent stem cells. This method could have the potential for analysis of three-dimensional structures and histological preservation in cultured cells.

Interaction of p53 and ASPPs regulates rhesus monkey embryonic stem cells conversion to neural fate concomitant with apoptosis

The tumor suppressor p53 is a key regulator of cell apoptosis and cell cycle arrest. Recent studies show that the delicate balance of p53 expression is important for neural tube defects, neuronal degeneration, embryonic lethality, as well as differentiation and dedifferentiation. Moreover, p53 showed different regulatory patterns between rodent and primate embryonic stem cells (ESCs). However, the role of p53 and apoptosis stimulating protein of p53 (ASPP) during neural differentiation (ND) from primate ESCs is still unknown. In this study, using an FGF-2 and/or HGF selectively containing ND culture systems for rhesus monkey ESCs (rESCs), the changes of p53 and ASPPs, and p53 targets, i.e. BAX and p21, were analyzed. Our results showed that the expression patterns of ASPP1/ASPP2 and iASPP were opposite in rESCs but similar in differentiated cells, and the expression of p53 was approximately consistent with BAX, but not p21. These findings indicate that the strong expression of iASPP in ESCs and weak expression of ASPP1/ASPP2 maintain the stability of stemness; and in ND niche, unimpaired iASPP may decrease its inhibition of ASPP1/ASPP2 expression, the interaction of p53 and ASPPs causing rESCs to convert towards a neural fate concomitant with apoptosis, but not to cell cycle arrest.

Characterization of Tetraploid Somatic Cell Nuclear Transfer-Derived Human Embryonic Stem Cells

Polyploidy is occurred by the process of endomitosis or cell fusion and usually represent terminally differentiated stage. Their effects on the developmental process were mainly investigated in the amphibian and fishes, and only observed in some rodents as mammalian model. Recently, we have established tetraploidy somatic cell nuclear transfer-derived human embryonic stem cells (SCNT-hESCs) and examined whether it could be available as a research model for the polyploidy cells existed in the human tissues. Two tetraploid hESC lines were artificially acquired by reintroduction of remained 1st polar body during the establishment of SCNT-hESC using MII oocytes obtained from female donors and dermal fibroblasts (DFB) from a 35-year-old adult male. These tetraploid SCNT-hESC lines (CHA-NT1 and CHA-NT3) were identified by the cytogenetic genotyping (91, XXXY,-6, t[2:6] / 92,XXXY,-12,+20) and have shown of indefinite proliferation, but slow speed when compared to euploid SCNT-hESCs. Using the eight Short Tendem Repeat (STR) markers, it was confirmed that both CHA-NT1 and CHA-NT3 lines contain both nuclear and oocyte donor genotypes. These hESCs expressed pluripotency markers and their embryoid bodies (EB) also expressed markers of the three embryonic germ layers and formed teratoma after transplantation into immune deficient mice. This study showed that tetraploidy does not affect the activities of proliferation and differentiation in SCNT-hESC. Therefore, tetraploid hESC lines established after SCNT procedure could be differentiated into various types of cells and could be an useful model for the study of the polyploidy cells in the tissues.

Naked Mole Rat Induced Pluripotent Stem Cells and Their Contribution to Interspecific Chimera

Naked mole rats (NMRs) are exceptionally long-lived, cancer-resistant rodents. Identifying the defining characteristics of these traits may shed light on aging and cancer mechanisms. Here, we report the generation of induced pluripotent stem cells (iPSCs) from NMR fibroblasts and their contribution to mouse-NMR chimeric embryos. Efficient reprogramming could be observed under N2B27+2i conditions. The iPSCs displayed a characteristic morphology, expressed pluripotent markers, formed embryoid bodies, and showed typical differentiation patterns. Interestingly, NMR embryonic fibroblasts and the derived iPSCs had propensity for a tetraploid karyotype and were resistant to forming teratomas, but within mouse blastocysts they contributed to both interspecific placenta and fetus. Gene expression patterns of NMR iPSCs were more similar to those of human than mouse iPSCs. Overall, we uncovered unique features of NMR iPSCs and report a mouse-NMR chimeric model. The iPSCs and associated cell culture systems can be used for a variety of biological and biomedical applications.

Tetraploid embryonic stem cells can contribute to the development of chimeric fetuses and chimeric extraembryonic tissues

Our study examined the in vivo chimeric and survival capacities of chimeras created by injecting tetraploid embryonic stem cells (ESCs) expressing green fluorescent protein (GFP) into diploid embryos. At 3.5 days post-coitum (dpc) and 4.5 dpc, the tetraploid ESCs were able to contribute to the inner cell mass (ICM) just as diploid ESCs tagged with GFP. At 6.5 dpc, 8.0 dpc and 10.5 dpc, the tetraploid ESCs manifested in the same location as the diploid ESCs. The GFP cells in the extraembryonic tissues and fetuses of tetraploid ESC chimeras were tetraploid as determined by fluorescence activated cell sorting (FACS). Furthermore, tetraploid ESCs contributed to the development of the placenta, embryolemma and umbilical cord at 13.5 dpc and 16.5 dpc; however, very less GFP cells were found in the fetuses of tetraploid ESC chimeras. We further found that the proliferation of tetraploid ESCs was slower than that of diploid ESCs. In addition, the relative mRNA expression in the three germ layers and the trophoblast was abnormal in the EBs of tetraploid ESCs compared with diploid ESCs. In short, slower proliferation and abnormal differentiation potential of tetraploid ESCs might be two of the reasons for their poor survival and chimeric capacities.

Effects of whole genome duplication on cell size and gene expression in mouse embryonic stem cells

Alterations in ploidy tend to influence cell physiology, which in the long-term, contribute to species adaptation and evolution. Polyploid cells are observed under physiological conditions in the nerve and liver tissues, and in tumorigenic processes. Although tetraploid cells have been studied in mammalian cells, the basic characteristics and alterations caused by whole genome duplication are still poorly understood. The purpose of this study was to acquire basic knowledge about the effect of whole genome duplication on the cell cycle, cell size, and gene expression. Using flow cytometry, we demonstrate that cell cycle subpopulations in mouse tetraploid embryonic stem cells (TESCs) were similar to those in embryonic stem cells (ESCs). We performed smear preparations and flow cytometric analysis to identify cell size alterations. These indicated that the relative cell volume of TESCs was approximately 2.2–2.5 fold that of ESCs. We also investigated the effect of whole genome duplication on the expression of housekeeping and pluripotency marker genes using quantitative real-time PCR with external RNA. We found that the target transcripts were 2.2 times more abundant in TESCs than those in ESCs. This indicated that gene expression and cell volume increased in parallel. Our findings suggest the existence of a homeostatic mechanism controlling the cytoplasmic transcript levels in accordance with genome volume changes caused by whole genome duplication.