Derivation and transcriptional profiling analysis of pluripotent stem cell lines from rat blastocysts

Production of large, defined genome modifications in rats by targeting rat embryonic stem cells

Rats were more frequently used than mice to model human disease before mouse embryonic stem cells (mESCs) revolutionized genetic engineering in mice. Rat ESCs (rESCs) were first reported over 10 years ago, yet they are not as frequently used as mESCs. CRISPR-based gene editing in zygotes is widely used in rats but is limited by the difficulty of inserting or replacing DNA sequences larger than about 10 kb. We report here the generation of germline-competent rESC lines from several rat strains. These rESC lines maintain their potential for germline transmission after serial targeting with bacterial artificial chromosome (BAC)-based targeting vectors, and CRISPR-Cas9 cutting can increase targeting efficiency. Using these methods, we have successfully replaced entire rat genes spanning up to 101 kb with the human ortholog.

Feeding role of mouse embryonic fibroblast cells is influenced by genetic background, cell passage and day of isolation

Mouse embryonic fibroblast (MEF) cells are commonly used as feeder cells to maintain the pluripotent state of stem cells. MEFs produce growth factors and provide adhesion molecules and extracellular matrix (ECM) compounds for cellular binding. In the present study, we compared the expression levels of Fgf2, Bmp4, ActivinA, Lif and Tgfb1 genes at the mRNA level and the level of Fgf2 protein secretion and Lif cytokine secretion at passages one, three and five of MEFs isolated from 13.5-day-old and 15.5-day-old embryos of NMRI and C57BL/6 mice using real-time PCR and enzyme-linked immunosorbent assay. We observed differences in the expression levels of the studied genes and secretion of the two growth factors in the three passages of MEFs isolated from 13.5-day-old and 15.5-day-old embryos, respectively. These differences were also observed between the NMRI and C57BL/6 strains. The results of this study suggested that researchers should use mice embryos that have different genetic backgrounds and ages, in addition to different MEF passages, when producing MEFs based on the application and type of their study.

Immortalized tumor derived rat fibroblasts as feeder cells facilitate the cultivation of male embryonic stem cells from the rat strain WKY/Ztm

Feeder cells are essential for the establishment and culture of pluripotent rat embryonic stem cells (ESC) in vitro. Therefore, we tested several fibroblast and epithelial cell lines derived from the female genital tract as feeder cells to further improve ESC culture conditions. The immortalized tumor derived rat fibroblast TRF-O3 cells isolated from a Dnd1-deficient teratoma were identified as optimal feeder cells supporting stemness and proliferation of rat ESC. The TRF-O3 cells were characterized as myofibroblasts by expression of fibroblast specific genes alpha-2 type I collagen, collagen prolyl 4-hydroxylase alpha (II), vimentin, S100A4, and smooth muscle α-actin. Culture of inner cell masses (ICM) derived from WKY/Ztm rat blastocysts in 2i-LIF medium on TRF-O3 feeder cells lacking LIF, SCF and FGF2 expression resulted in pluripotent and germ-line competent rat ESC lines. Therein, genotyping confirmed up to 26% male ESC lines. On the other hand the TRF-O3 specific BMP4 expression was correlated with transcriptional activity of the mesodermal marker T-brachyury and the ectoderm specific nestin in the ESC line ES21 demonstrating mesodermal or ectodermal cell lineage differentiation processes within the ESC population. Substitution of 2i-LIF by serum-containing YPAC medium supplemented with TGF-β and rho kinase inhibitors or by 4i medium in combination with TRF-O3 feeder cells led to enhanced differentiation of ES21 cells and freshly isolated ICMs. These results suggest that the ESC culture conditions using TRF-O3 feeder cells and 2i-LIF medium supported the establishment of male ESC lines from WKY/Ztm rats, which represent a favored, permissive genetic background for rat ESC culture.

A focused microarray for screening rat embryonic stem cell lines

Here, we describe a focused microarray for screening rat embryonic stem cells (ESCs) and provide validation data that this array can distinguish undifferentiated rat ESCs from rat trophoblast stem (TS) cells, rat extraembryonic endoderm cells, mouse embryonic fibroblast feeder cells, and differentiated rat ESCs. Using this tool, genuine rat ESC lines, which have been expanded in a conventional rat ESC medium containing two inhibitors (2i), for example, glycogen synthase kinase 3 (GSK3) and mitogen-activated protein kinase (MEK) inhibitors, and leukemia inhibitory factor, and genuine rat ESCs, which have been expanded in rat ESC medium containing four inhibitors (4i), for example, GSK3, MEK, Alk5, and Rho-associated kinase inhibitors were compared; as were genuine rat ESCs from 4 different strains of rats. Expression of Cdx2, a gene associated with trophoblast determination, was observed in genuine, undifferentiated rat ESCs from 4 strains and from both 2i and 4i ESC derivation medium. This finding is in contrast to undifferentiated mouse ESCs that do not express Cdx2. The rat ESC focused microarray described in this report has utility for rapid screening of rat ESCs. This tool will enable optimization of culture conditions in the future.

Isolation of rat embryonic stem-like cells: a tool for stem cell research and drug discovery

The establishment of rat embryonic stem cells constitutes a precious tool since rat has been extensively used in biomedical research, in particular for the generation of human neurodisease animal models. Up to now only a few studies have described the isolation of rat embryonic stem-like cells. One out of 9 isolated rat embryonic stem-like cell lines (B1-RESC) obtained from a 4.5-day post-coitum blastocyst were extensively characterized and kept in culture for up to 80 passages on feeders with LIF. The stable growth of these cells and the expression of pluripotent markers were confirmed up to a high number of passages in culture, also in the absence of feeders and LIF. B1-RESC expresses the three germ layers markers both in vitro, within differentiating embryoid bodies, and in vivo through teratoma formation. Collectively, the B1-RESC line with a stable near-diploid karyotype can be used as a highly sensitive tool for testing anti-proliferative molecules.

Mouse and human pluripotent stem cells and the means of their myogenic differentiation

Pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem cells, are an important tool in the studies focusing at the differentiation of various cell types, including skeletal myoblasts. They are also considered as a source of the cells that due to their pluripotent character and availability could be turned into any required tissue and then used in future in regenerative medicine. However, the methods of the derivation of some of cell types from pluripotent cells still need to be perfected. This chapter summarizes the history and current advancements in the derivation and testing of pluripotent stem cells-derived skeletal myoblasts. It focuses at the in vitro methods allowing the differentiation of stem cells grown in monolayer or propagated as embryoid bodies, and also at in vivo tests allowing the verification of the functionality of obtained skeletal myoblasts.

In vitro differentiation of rat embryonic stem cells into functional cardiomyocytes

The recent breakthrough in the generation of rat embryonic stem cells (rESCs) opens the door to application of gene targeting to create models for the study of human diseases. In addition, the in vitro differentiation system from rESCs into derivatives of three germ layers will serve as a powerful tool and resource for the investigation of mammalian development, cell function, tissue repair, and drug discovery. However, these uses have been limited by the difficulty of in vitro differentiation. The aims of this study were to establish an in vitro differentiation system from rESCs and to investigate whether rESCs are capable of forming terminal-differentiated cardiomyocytes. Using newly established rESCs, we found that embryoid body (EB)-based method used in mouse ESC (mESC) differentiation failed to work for the serum-free cultivated rESCs. We then developed a protocol by combination of three chemical inhibitors and feeder-conditioned medium. Under this condition, rESCs formed EBs, propagated and differentiated into three embryonic germ layers. Moreover, rESC-formed EBs could differentiate into spontaneously beating cardiomyocytes after plating. Analyses of molecular, structural, and functional properties revealed that rESC-derived cardiomyocytes were similar to those derived from fetal rat hearts and mESCs. In conclusion, we successfully developed an in vitro differentiation system for rESCs through which functional myocytes were generated and displayed phenotypes of rat fetal cardiomyocytes. This unique cellular system will provide a new approach to study the early development and cardiac function, and serve as an important tool in pharmacological testing and cell therapy.

Rat blastocyst-derived stem cells are precursors of embryonic and extraembryonic lineages

Despite recent advances in the derivation of rat embryonic stem cells, clear comprehension of the timing and mechanisms underlying rat early embryo lineage selection is lacking. We have previously shown the in vivo contribution of rat embryonic stem-like cells exclusively to developing extraembryonic tissues. To elucidate possible mechanisms governing the in vitro and in vivo behaviors of these rat blastocyst-derived stem cells, we evaluated their developmental capacity by using several approaches. Molecular marker analysis demonstrated the expression profile of genes characterizing not only pluripotency but also extraembryonic endoderm and trophoblast. In vitro differentiation through embryoid body formation showed in vitro pluripotent capacity through differentiation into derivatives of all three embryonic germ layers. Following either blastocyst injection, diploid or tetraploid aggregation, and embryo transfer, these rat blastocyst-derived stem cells also demonstrated in vivo multipotency through contribution to multiple developmentally distinct extraembryonic lineages. Features of phenotypic heterogeneity were revealed following examination of cell line morphology and culture behavior, as well as quantitative analysis of marker expression in discrete undifferentiated and differentiated populations of cells by flow cytometry. We demonstrate for the first time that stem cells derived from the rat blastocyst have the ability to contribute to the embryonic and extraembryonic lineages. Together, these results provide a valuable new model for rat stem cell biology and for the elucidation of early lineage selection in the embryo.

Factors regulating pluripotency and differentiation in early mammalian embryos and embryo-derived stem cells

Mammalian development relies on the cellular proliferation and precisely orchestrated differentiation processes. In preimplantation embryos preservation of the pluripotent state and timely onset of differentiation are secured by specific mechanisms involving such factors as OCT₄, NANOG, SOX₂, or SALL₄. The pluripotency-sustaining cellular machinery is operational not only in the cells of preimplantation embryos but also in embryo-derived embryonic stem cells and epiblast stem cells. However, certain variations in the execution of pluripotency exist and result in the differences not only between embryonic cells and stem cells of the same mammalian species, but also between those of different mammalian species, such as mouse, rat, bank vole, or humans. In this review we describe the involvement of exogenous stimuli (e.g., LIF, WNT, BMP, FGF, and Activin) and function of intrinsic factors (e.g., OCT₄, NANOG, SOX₂, SALL₄) in the regulation of pluripotency in mammalian preimplantation embryos and pluripotent stem cells derived from them. We also focus at the existence of species-specific differences at the level of growth factor requirements, signaling pathways, and transcription factors. Thus, we discuss differences in mechanisms which understanding is one of the necessary steps allowing establishment of methods of efficient derivation, defined in vitro culture conditions, and possible future therapeutic applications of pluripotent stem cells.

Assisted Reproductive Technologies (ART) with baboons generate live offspring: a nonhuman primate model for ART and reproductive sciences

Human reproduction has benefited significantly by investigating nonhuman primate (NHP) models, especially rhesus macaques. To expand the Old World monkey species available for human reproductive studies, we present protocols in baboons, our closest Old World primate relatives, for assisted reproductive technologies (ART) leading to live born offspring. Baboons complement rhesus by confirming or modifying observations generated in humans often obtained by the study of clinically discarded specimens donated by anonymous infertility patient couples. Here, baboon ART protocols, including oocyte collection, in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), preimplantation development to blastocyst stage, and embryo transfer techniques are described. With baboon ART methodologies in place, motility during baboon fertilization was investigated by time-lapse video microscopy (TLVM). The first ART baboons produced by ICSI, a pair of male twins, were delivered naturally at 165 days postgestation. Genetic testing of these twins confirmed their ART parental origins and demonstrated that they are unrelated fraternal twins not identicals. These results have implications for ART outcomes, embryonic stem cell (ESC) derivation, and reproductive sciences.

Characterization of trophoblast and extraembryonic endoderm cell lineages derived from rat preimplantation embryos

BACKGROUND

Previous attempts to isolate pluripotent cell lines from rat preimplantation embryo in mouse embryonic stem (ES) cell culture conditions (serum and LIF) were unsuccessful, however the resulting cells exhibited the expression of such traditional pluripotency markers as SSEA-1 and alkaline phosphatase. We addressed the question, which kind of cell lineages are produced from rat preimplantation embryo under "classical" mouse ES conditions.

RESULTS

We characterized two cell lines (C5 and B10) which were obtained from rat blastocysts in medium with serum and LIF. In the B10 cell line we found the expression of genes known to be expressed in trophoblast, Cdx-2, cytokeratin-7, and Hand-1. Also, B10 cells invaded the trophectodermal layer upon injection into rat blastocysts. In contrast to mouse Trophoblast Stem (TS) cells proliferation of B10 cells occurred independently of FGF4. Cells of the C5 line expressed traditional markers of extraembryonic-endoderm (XEN) cells, in particular, GATA-4, but also the pluripotency markers SSEA-1 and Oct-4. C5 cell proliferation exhibited dependence on LIF, which is not known to be required by mouse XEN cells.

CONCLUSIONS

Our results confirm and extend previous findings about differences between blastocyst-derived cell lines of rat and mice. Our data show, that the B10 cell line represents a population of FGF4-independent rat TS-like cells. C5 cells show features that have recently become known as characteristic of rat XEN cells. Early passages of C5 and B10 cells contained both, TS and XEN cells. We speculate, that mechanisms maintaining self-renewal of cell lineages in rat preimplantation embryo and their in vitro counterparts, including ES, TS and XEN cells are different than in respective mouse lineages.

Developmental potential of rat extraembryonic stem cells

We have previously found that certain stem cells that are derived from rat blastocysts and named extraembryonic endoderm precursor (XEN-P) cells show a unique molecular signature sharing some of the characteristics of embryonic stem cells (ES), trophoblast stem cells (TS), and extraembryonic endoderm stem cells (XEN). These XEN-P cells are positive for AP, SSEA1, Oct4, and Rex1 markers similar to ES cells and also express signature markers of TS-eomesodermin (Eomes) and XEN-Gata6. Here we show that these cells integrate into the visceral and parietal extraembryonic endoderm lineages as well as into the inner cell mass (ICM), the primitive endoderm, and the polar and mural trophectoderm (TE) of cultured embryos. In addition, we find that the XEN-P cells colonize yolk sac and contribute to trophoblast lineages of postimplantation embryos following transfer to surrogate mothers. We also find that the XEN-P cell culture propagates by shedding cell clusters into the media in addition to typical expansion of colonies. Interestingly, the cell cultures exist as mixed populations of two interconvertible phenotypes of flat and round cells with preferential expression of stem cell markers Oct4 and SSEA1 in round cells. We believe these cells represent a metastable stage during ICM cellular segregation. These results are important for developing hypotheses of cell fate plasticity in the ICM and provide a model for the study of development and differentiation along the extraembryonic lineages.

Isolation of Oct4-expressing extraembryonic endoderm precursor cell lines

BACKGROUND

The extraembryonic endoderm (ExEn) defines the yolk sac, a set of membranes that provide essential support for mammalian embryos. Recent findings suggest that the committed ExEn precursor is present already in the embryonic Inner Cell Mass (ICM) as a group of cells that intermingles with the closely related epiblast precursor. All ICM cells contain Oct4, a key transcription factor that is first expressed at the morula stage. In vitro, the epiblast precursor is most closely represented by the well-characterized embryonic stem (ES) cell lines that maintain the expression of Oct4, but analogous ExEn precursor cell lines are not known and it is unclear if they would express Oct4.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report the isolation and characterization of permanently proliferating Oct4-expressing rat cell lines ("XEN-P cell lines"), which closely resemble the ExEn precursor. We isolated the XEN-P cell lines from blastocysts and characterized them by plating and gene expression assays as well as by injection into embryos. Like ES cells, the XEN-P cells express Oct4 and SSEA1 at high levels and their growth is stimulated by leukemia inhibitory factor, but instead of the epiblast determinant Nanog, they express the ExEn determinants Gata6 and Gata4. Further, they lack markers characteristic of the more differentiated primitive/visceral and parietal ExEn stages, but exclusively differentiate into these stages in vitro and contribute to them in vivo.

CONCLUSIONS/SIGNIFICANCE

Our findings (i) suggest strongly that the ExEn precursor is a self-renewable entity, (ii) indicate that active Oct4 gene expression (transcription plus translation) is part of its molecular identity, and (iii) provide an in vitro model of early ExEn differentiation.

Germline-competent mouse-induced pluripotent stem cell lines generated on human fibroblasts without exogenous leukemia inhibitory factor

Induced pluripotent stem (iPS) cells have attracted enormous attention due to their vast potential in regenerative medicine, pharmaceutical screening and basic research. Most prior established iPS cell lines were derived and maintained on mouse embryonic fibroblast (MEF) cells supplemented with exogenous leukemia inhibitory factor (LIF). Drawbacks of MEF cells impede optimization as well as dissection of reprogramming events and limit the usage of iPS cell derivatives in therapeutic applications. In this study, we develop a reproducible protocol for efficient reprogramming mouse neural progenitor cells (NPCs) on human foreskin fibroblast (HFF) cells via retroviral transfer of human transcriptional factors OCT4/SOX2/KLF4/C-MYC. Two independent iPS cell lines are derived without exogenous LIF. They display typical undifferentiated morphology and express pluripotency markers Oct4 and Sox2. Transgenes are inactivated and the endogenous Oct4 promoter is completely demethylated in the established iPS cell lines, indicating a fully reprogrammed state. Moreover, the iPS cells can spontaneously differentiate or be induced into various cell types of three embryonic germ layers in vitro and in vivo when they are injected into immunodeficient mice for teratoma formation. Importantly, iPS cells extensively integrate with various host tissues and contribute to the germline when injected into the blastocysts. Interestingly, these two iPS cell lines, while both pluripotent, exhibit distinctive differentiation tendencies towards different lineages. Taken together, the data describe the first genuine mouse iPS cell lines generated on human feeder cells without exogenous LIF, providing a reliable tool for understanding the molecular mechanisms of nuclear reprogramming.

Generation of pig induced pluripotent stem cells with a drug-inducible system

Domesticated ungulate pluripotent embryonic stem (ES) cell lines would be useful for generating precise gene-modified animals. To date, many efforts have been made to establish domesticated ungulate pluripotent ES cells from early embryos without success. Here, we report the generation of porcine-induced pluripotent stem (iPS) cells using drug-inducible expression of defined factors. We showed that porcine iPS cells expressed alkaline phosphatase, SSEA3, SSEA4, Tra-1-60, Tra-1-81, Oct3/4, Nanog, Sox2, Rex1 and CDH1. Pig iPS cells expressed high levels of telomerase activity and showed normal karyotypes. These cells could differentiate into cell types of all three germ layers in vitro and in teratomas. Our study reveals properties of porcine pluripotent stem cells that may facilitate the eventual establishment of porcine ES cells. Moreover, the porcine iPS cells produced may be directly useful for the generation of precise gene-modified pigs.

Cloning and Characterization of 3.1kb Promoter Region of the Oct4 Gene from the Fischer 344 Rat

Here, the role of methylation in regulation of rat Oct4 gene was evaluated during embryonic development, in adult tissues and in embryo-derived cells. First, the region 3.1 kb upstream to the rat Oct4 ATG site was cloned and sequenced. The rat Oct4 upstream sequence was similar to that in bovine, mouse and human with two upstream elements: proximal (PE) and distal enhancers (DE) and four homology conserved regions (CR1-4). The conserved regions in the rat have 69% - 96% homology with bovine, human, mouse sequences. Next, the methylation pattern in the promoter was determined during embryonic development, in adult tissues, in rat embryonic stem cell (ESC)-like cells and umbilical cord-derived cells (the feeder for ESC-like cells) using the bisulfite method and DNA sequencing. The promoter was methylated in adult and fetal tissues, and in days post coitus (DPC) 10.5 and 12.5 embryos and hypomethylated in DPC4.5 embryos and in rat ESC-like cells. The expression of Oct4 was evaluated by qRT-PCR. DPC4.5 embryos and rat ESC-like cells had higher expression of the Oct4 gene compared to DPC10.5 and 12.5 embryos, adult tissues and embryoid bodies derived from rat ESC-like cells. Thus, the methylation status correlated with the qRT-PCR results. These results indicate that the rat Oct4 3.1kb promoter region is organized and contains transcription binding and regulatory sites similar to those described for bovine, mouse and human. The rat Oct4 promoter is methylated during embryonic development after 4.5 DPC and during differentiation of rat ESC-like cells to embryoid bodies.