Expression Of Rex1 Research Articles

Effect of melatonin on mRNA expressions of transcription factors in murine embryonic stem cells

Murine embryonic stem (ES) cells constitute a versatile biological system that has facilitated major advances in the fields of cell and developmental biology. Although melatonin has a wide variety of biological functions, its effect on ES cells is still unknown. In this study, we examined the effects of melatonin on transcription factors of ES cells (ES-E14TG2a cells) using an in vitro culture system. We found that melatonin affected cellular proliferation and Akt phosphorylation. Melatonin treatment also increased Bcl-2 expression and suppressed Bax expression and decreased phosphorylation of GSK α/β. The transcription factor Oct4, which contains the POU (N-terminal to homeobox) domain, and the transcription factor Sox2, the zinc finger transcription factor Zfp206, and the zinc finger gene REX-1 (Znf42), which contain the high mobility group (HMG) domain, are all important for cellular pluripotency and pre-implantation development. In this study, melatonin treatment influenced Oct4 and REX-1 expression at day 1 but not significantly at days 2 and 3. In addition, Sox2 and Zfp206 expressions did not change over the course of melatonin treatment. Taken together, melatonin may affect Akt activation but does not influence the mRNA expressions of Oct4, REX-1, Sox2, or Zfp206, suggesting that melatonin may stimulate proliferation of ES-E14TG2a cells via Akt phosphorylation.

A comprehensive characterization study of human bone marrow mscs with an emphasis on molecular and ultrastructural properties

Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) continue to draw attention of researchers in the fields of basic science and medicine due to their indispensible regenerative, reparative, angiogenic, anti-apoptotic, and immunosuppressive properties, all of which collectively point out their enormous therapeutic potential. There is still, however, a need for further investigation of their characteristics to broaden their field of use and learn much more about how to control their fate and improve their therapeutic effectiveness. hBM-MSCs were extensively characterized in terms of their growth characteristics, genetic stability, and differentiation capability to the mesodermal and ectodermal cell lineages; a special emphasis was given to their phenotypic and ultrastructural properties. Expression of embryonic stem cell markers Oct4, Rex-1, FoxD-3, Sox2, and Nanog was shown with real-time PCR. Transmission electron microscopy revealed the ultrastructural characteristics of hBM-MSCs; they had pale, irregularly shaped and large euchromatic nuclei, and two distinct areas in their cytoplasm: an intensely stained inner zone rich in mitochondria and rough endoplasmic reticulum (rER) with dilated cisternae and a relatively peripheral zone poor in organelles. hBM-MSCs expressed adipogenic (adipophilin and PPARγ), myogenic (desmin, myogenin, α-SMA), neurogenic (γ-enolase, MAP2a,b, c-fos, nestin, NF-H, NF-L, GFAP, β3-tubulin), osteogenic (osteonectin, osteocalcin, osteopontin, Runx-2, type I collagen), and chondrogenic (type II collagen, SOX9) markers either at RNA or protein level even under basal conditions, without any stimulation towards differentiation. The differentiation potential of hBM-MSCs to adipogenic, osteogenic, and neurogenic lineages was shown by using the relevant differentiation factors.

A Genetically Engineered STO Feeder System Expressing E-Cadherin and Leukemia Inhibitory Factor for Mouse Pluripotent Stem Cell Culture

Embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are usually cultured on mouse embryonic fibroblasts (MEFs) isolated from fetuses. MEFs are primary cells and can only be cultured for several passages before senescence. Although the STO mouse stromal cell line has been used as a MEF substitute, performance of a STO feeder layer for ES/iPS cell culture is inferior to a MEF feeder layer. Thus, the development of effective feeder systems may be beneficial for advancing stem cell technology using ES/iPS cells. We established a STO feeder cell line expressing mouse leukemia inhibitory factor (LIF) and mouse E-cadherin (designated as STO/EL cells). ES/iPS cells were cultured on STO/EL feeder cells without LIF addition to the medium, while maintaining the expression of stem cell markers, Oct3/4, Nanog and Rex1. Quantitative evaluation of feeder performance by an alkaline phosphatase-positive colony-forming assay revealed that the colony forming efficiency was comparable to that of the conventional and most reliable culture method using MEFs with LIF addition. STO/EL cells can be used as an efficient feeder system for supporting ES/iPS cell culture in an undifferentiated state. The STO/EL feeder system may contribute toward medical and biological research of ES/iPS cells.

Activation of Pluripotency Genes in Human Fibroblast Cells by a Novel mRNA Based Approach

BackgroundSeveral methods have been used to induce somatic cells to re-enter the pluripotent state. Viral transduction of reprogramming genes yields higher efficiency but involves random insertions of viral sequences into the human genome. Although induced pluripotent stem (iPS) cells can be obtained with the removable PiggyBac transposon system or an episomal system, both approaches still use DNA constructs so that resulting cell lines need to be thoroughly analyzed to confirm they are free of harmful genetic modification. Thus a method to change cell fate without using DNA will be very useful in regenerative medicine.Methodology/Principal FindingsIn this study, we synthesized mRNAs encoding OCT4, SOX2, cMYC, KLF4 and SV40 large T (LT) and electroporated them into human fibroblast cells. Upon transfection, fibroblasts expressed these factors at levels comparable to, or higher than those in human embryonic stem (ES) cells. Ectopically expressed OCT4 localized to the cell nucleus within 4 hours after mRNA introduction. Transfecting fibroblasts with a mixture of mRNAs encoding all five factors significantly increased the expression of endogenous OCT4, NANOG, DNMT3β, REX1 and SALL4. When such transfected fibroblasts were also exposed to several small molecules (valproic acid, BIX01294 and 5′-aza-2′-deoxycytidine) and cultured in human embryonic stem cell (ES) medium they formed small aggregates positive for alkaline phosphatase activity and OCT4 protein within 30 days.Conclusion/SignificanceOur results demonstrate that mRNA transfection can be a useful approach to precisely control the protein expression level and short-term expression of reprogramming factors is sufficient to activate pluripotency genes in differentiated cells.

315 MELATONIN EFFECTS ON THE PROLIFERATION AND DIFFERENTIATION OF MOUSE EMBRYONIC STEM CELLS

Mouse embryonic stem (ES) cells constitute a versatile biological system that can facilitate major advances in the fields of cell and developmental biology. Several studies have been performed to determine whether melatonin can affect ex vivo and in vitro proliferation and differentiation of stem cells (mesenchymal and neural stem cells derived human, rats, and mice), but its effect on ES cells is largely unknown. Thus, we further examined in this study the effects of melatonin at biological or pharmacological concentrations (100 or 200 μM) on the proliferation and differentiation of ES cells (ES-E14TG2a cells) using an in vitro culture system (n = 3) by Western blot analysis and real-time PCR. We found that melatonin at 100 and 200 μM resulted in cellular proliferation and phosphorylation of ERK and Akt, respectively. Melatonin treatment also increased Bcl-2 expression and suppressed Bax gene expression and increased phosphorylation of GSK α/β. The transcription factor Oct-4, which contains the POU (N-terminal to homeobox) domain, and the transcription factor Sox2, the zinc finger transcription factor Zfp206, and the zinc finger gene REX-1 (Znf42), which contain the high mobility group domain, are all important for cellular pluripotency and preimplantation development. In this study, melatonin (100 μM) treatment induced Oct-4 and REX-1 expression at day 1 but not at days 2 and 3. In addition, Sox2 and Zfp206 expressions were not altered following melatonin treatment. Taken together, these results suggest that melatonin may affect Akt phosphorylation and stem cell proliferation at biological or pharmacological concentrations.

291 ISOLATION AND CHARACTERIZATION OF MESENCHYMAL STEM CELLS DERIVED FROM HUMAN AMNIOTIC FLUID

Adult stem cells have the capacity to differentiate into several different cell types, although their differentiation potential is limited compared with that of embryonic stem cells. Thus, adult stem cells are regarded as an exciting source for new cell therapies. Recent observations also indicate that stem cells derived from second-trimester amniocentesis are pluripotent – capable of differentiating into multiple lineages, including representatives of all 3 embryonic germ layers. In addition, amniotic fluid stem cells can be used in the generation of disease- or patient-specific stem cells, and amniotic fluid stem cells could be an ideal source for autologous cell replacement therapy in the later life of the fetus. The aim of the present study was to investigate isolation and characterisation of human amniotic fluid-derived mesenchymal stem cells (hAFS). We successfully isolated and characterised hAFS. Amniotic fluid samples were collected in the second trimester (median gestational age: 16 weeks, range: 15–17 weeks) for prenatal diagnosis. Specimens (2 mL) were centrifuged and incubated in low-glucose DMEM supplemented with 10% FBS, 25 ng of basic fibroblast growth factor, and 10 ng of epidermal growth factor at 37°C with 5% CO2. Human amniotic fluid cell (passage 6) expression of stem cell specific markers OCT-4, SOX2, Rex1, FGF4, and NANOG was confirmed by RT-PCR. Flow cytometric analysis showed that hAFS (passage 10) were positive for CD44, CD29, CD146, STRO1, and CD90 but negative for CD19. Immunocytochemical analysis of hAFS (passage 11) also showed the expression of OCT-4, SSEA-1, CD44, CD29, CD146, STRO1, and CD90, but hAFS were negative for CD19 and CD14. In conclusion, according to the previous studies on other mammalians, hAFS are an appropriate source of pluripotent stem cells. Here, we demonstrated that hAFS have a high expression of stem cell specific marker, including embryonic stem cell marker and mesenchymal stem cell marker. Therefore, amniotic fluid may be a suitable alternative source of multipotent stem cells.

The Efficient Generation of Cell Lines from Bovine Parthenotes

The generation of embryonic stem cell (ESC) lines from parthenogenetically activated oocytes can provide transplantable cells, which are immunocompatible for the oocyte donors as well as an invaluable tool for genetic engineering and epigenetic studies. We report the efficient isolation of eight putative bovine parthenogenetic embryonic stem cell (bpESC) lines from 15 in vitro produced parthenotes. Five of these cell lines were maintained for more than 15 passages (>140 days) and analyzed. The cells displayed typical ESC morphology, stained positive for alkaline phosphate by histochemical staining, expressed Oct4, Nanog, and either stage-specific embryonic antigens, SSEA1, or SSEA4, detected by immunofluorescence staining. RT-PCR analysis of the cells demonstrated expression of Oct4, Rex1, SSEA1, and ALP. All the cell lines except one had a normal karyotype of 60, XX. The cells differentiated in suspension culture to form embryoid bodies (EBs) expressing markers of the three embryonic germ layers as assessed by RT-PCR. In conclusion, we report efficient derivation of putative ESCs from bovine parthenogenetic embryos. The cells express pluripotent markers, have the ability to form EBs, and differentiate into cells of the three embryonic germ layers. This is the first report of characterized putative parthenogenetic bovine ESC lines.

Undifferentiated Propagation of the Human Embryonic Stem Cell Lines, H1 and HSF6, on Human Placenta-Derived Feeder Cells Without Basic Fibroblast Growth Factor Supplementation

In order for human embryonic stem cells (hESCs) to be cultured on mouse embryonic fibroblast (MEFs) feeder cells, continuous basic fibroblast growth factor (bFGF) supplementation is required. However, the role of bFGF in a culture system using human-derived feeder cells has not been evaluated until now. In this study, we propagated the widely used hESC lines, H1 and HSF6, on human placenta-derived feeder cells (HPCs) without exogenous bFGF supplementation, and were able to propagate hESCs on HPC feeders up to 50 passages. The absence of bFGF in culture media did not interrupt the undifferentiated propagation and the expression of pluripotent stem cell markers ALP, SSEA-4, TRA-60, Oct-4, Nanog, and Rex-1, as well as the formation of embryoid bodies (EBs) and their differentiation potential. In contrast, hESCs cocultured with MEF feeders could not propagate and form EBs without exogenous bFGF supplementation. Expression of bFGF and the activation of the ERK1/2-c-Fos/c-Jun pathway, which is known as the signaling pathway of bFGF, were identifiable not only in hESCs cultured in bFGF-containing media regardless of feeder cell type, but also in hESCs cocultured with HPC feeder cells in media without bFGF. These findings may support the hypothesis that HPC feeder cells enhance endogenous bFGF production and activation of the ERK1/2-c-Fos/c-Jun pathway, which suggests that HPCs have an additional advantage in their hESC propagation compared with MEF.

The Efficacy of Human Placenta as a Source of the Universal Feeder in Human and Mouse Pluripotent Stem Cell Culture

The use of a mouse embryonic fibroblast (MEF) feeder for culture of embryonic stem cells (ESCs) is a widely accepted method, regardless of the ESCs' origin and type. In this study, we performed the undifferentiated propagation of human ES cell lines (hESCs, H1, and HSF6) and mouse ES cell lines (mESCs, D3, and CE3), which were previously maintained on an MEF feeder, using human placenta-derived fibroblast-like cell (HPC) feeders originated from chorionic villi of women who had undergone therapeutic abortion due to known maternal disease that is aggravated by pregnancy. Moreover, we tried to introduce the HPC feeder for the establishment of inducible pluripotent stem cells (iPSCs) from human placental mesenchymal stem cells (MSCs). On the HPC feeder we were able to propagate ESCs and iPSCs colonies as an undifferentiated state up to the 50th passage and 20th passage, respectively. Maintenance of undifferentiated ESCs was identified by the expression of ALP, SSEA-1, SSEA-4, TRA-81, TRA-60, Oct-4, Nanog, or Rex-1. Also, addition of leukemia inhibitory factor was not required for undifferentiated propagation of mESCs on the HPC feeder. The efficiency and expression of three germ layer markers of embryoid bodies (EBs) from ESCs were satisfactory in both the MEF and HPC group. EBs formed from iPSCs were scant, and differentiation to the three germ layers was identifiable by reverst transcription-polymerase chain reactio (RT-PCR) only in the HPC group. In conclusion, the HPC feeder can efficiently support the undifferentiated propagation of hESCs, mESCs, and iPSCs, suggesting that human placenta may be a useful source of universal feeder cells for hESC, mESC, and iPSC culture.

REX-1 Expression and p38 MAPK Activation Status Can Determine Proliferation/Differentiation Fates in Human Mesenchymal Stem Cells

BackgroundREX1/ZFP42 is a well-known embryonic stem cell (ESC) marker. However, the role of REX1, itself, is relatively unknown because the function of REX1 has only been reported in the differentiation of ESCs via STAT signaling pathways. Human mesenchymal stem cells (hMSCs) isolated from young tissues and cancer cells express REX1.Methodology/Principal FindingHuman umbilical cord blood-derived MSCs (hUCB-MSCs) and adipose tissue-derived MSCs (hAD-MSCs) strongly express REX1 and have a lower activation status of p38 MAPK, but bone marrow-derived MSCs (hBM-MSCs) have weak REX1 expression and higher activation of p38 MAPK. These results indicated that REX1 expression in hMSCs was positively correlated with proliferation rates but inversely correlated with the phosphorylation of p38 MAPK. In hUCB-MSCs, the roles of REX1 and p38 MAPK were investigated, and a knockdown study was performed using a lentiviral vector-based small hairpin RNA (shRNA). After REX1 knockdown, decreased cell proliferation was observed. In REX1 knocked-down hUCB-MSCs, the osteogenic differentiation ability deteriorated, but the adipogenic potential increased or was similar to that observed in the controls. The phosphorylation of p38 MAPK in hUCB-MSCs significantly increased after REX1 knockdown. After p38 MAPK inhibitor treatment, the cell growth in REX1 knocked-down hUCB-MSCs almost recovered, and the suppressed expression levels of CDK2 and CCND1 were also restored. The expression of MKK3, an upstream regulator of p38 MAPK, significantly increased in REX1 knocked-down hUCB-MSCs. The direct binding of REX1 to the MKK3 gene was confirmed by a chromatin immunoprecipitation (ChIP) assay.Conclusions/SignificanceThese findings showed that REX1 regulates the proliferation/differentiation of hMSCs through the suppression of p38 MAPK signaling via the direct suppression of MKK3. Therefore, p38 MAPK and REX-1 status can determine the cell fate of adult stem cells (ASCs). These results were the first to show the role of REX1 in the proliferation/differentiation of ASCs.

Transcriptional regulation of Rex1 (zfp42) in normal prostate epithelial cells and prostate cancer cells

Rex1 (zfp42) was identified by our laboratory because of its reduced expression in F9 teratocarcinoma stem cells after retinoic acid (RA) treatment. The Rex1 (Zfp42) gene is currently widely used as a marker of embryonic stem cells. We compared the transcriptional regulation of the human Rex1 gene in NTera-2 (NT-2) human teratocarcinoma, normal human prostate epithelial cells (PrEC), and prostate cancer cells (PC-3) by promoter/luciferase analyses. Oct4, Sox2, Nanog, and Dax1 transcripts are expressed at higher levels in NT-2 and PrEC cells than in PC-3 cells. Co-transfection analyses showed that YY1 and Rex1 are positive regulators of hRex1 transcription in NT-2 and PrEC cells, whereas Nanog is not. Serial deletion constructs of the hRex1 promoter were created and analyzed, by which we identified a potential negative regulatory site that is located between -1 and -0.4 kb of the hRex1 promoter. We also delineated regions of the hRex1 promoter between -0.4 kb and the TSS that, when mutated, reduced transcriptional activation; these are putative Rex1 binding sites. Mutation of a putative Rex1 binding site in electrophoretic mobility shift assays (EMSA) resulted in reduced protein binding. Taken together, our results indicate that hRex1 binds to the hRex1 promoter region at -298 bp and positively regulates hRex1 transcription, but that this regulation is lost in PC-3 human prostate cancer cells. This lack of positive transcriptional regulation by the hRex1 protein may be responsible for the lack of Rex1 expression in PC-3 prostate cancer cells.

Induction of Stem Cell Gene Expression in Adult Human Fibroblasts without Transgenes

Reprogramming of differentiated somatic cells into induced pluripotent stem (iPS) cells has potential for derivation of patient-specific cells for therapy as well as for development of models with which to study disease progression. Derivation of iPS cells from human somatic cells has been achieved by viral transduction of human fibroblasts with early developmental genes. Because forced expression of these genes by viral transduction results in transgene integration with unknown and unpredictable potential mutagenic effects, identification of cell culture conditions that can induce endogenous expression of these genes is desirable. Here we show that primary adult human fibroblasts have basal expression of mRNA for OCT4, SOX2, and NANOG. However, translation of these messages into detectable proteins and their subcellular localization depends on cell culture conditions. Manipulation of oxygen concentration and FGF2 supplementation can modulate expression of some pluripotency related genes at the transcriptional, translational, and cellular localization level. Changing cell culture condition parameters led to expression of REX1, potentiation of expression of LIN28, translation of OCT4, SOX2, and NANOG, and translocation of these transcription factors to the cell nucleus. We also show that culture conditions affect the in vitro lifespan of dermal fibroblasts, nearly doubling the number of population doublings before the cells reach replicative senescence. Our results suggest that it is possible to induce and manipulate endogenous expression of stem cell genes in somatic cells without genetic manipulation, but this short-term induction may not be sufficient for acquisition of true pluripotency. Further investigation of the factors involved in inducing this response could lead to discovery of defined culture conditions capable of altering cell fate in vitro. This would alleviate the need for forced expression by transgenesis, thus eliminating the risk of mutagenic effects due to genetic manipulation.

Analysis of Rex1 (zfp42) function in embryonic stem cell differentiation

Rex1 (zfp42) is a zinc finger protein expressed primarily in undifferentiated stem cells, both in the embryo and the adult. Upon all-trans retinoic acid induced differentiation of murine embryonic stem (ES) cells, Rex1 mRNA levels decrease several fold. To characterize the function(s) of Rex1 more extensively, we generated Rex1 double knockout ES cell lines. The disruption of the Rex1 gene enhanced the expression of ectoderm, mesoderm, and endoderm markers as compared to wild-type (Wt) cells. We propose that Rex1 acts to reduce retinoic acid induced differentiation in ES cells. We performed microarray analyses on Wt and Rex1-/- cells cultured in the presence or absence of LIF to identify potential Rex1 targets. We also evaluated gene expression in a Wt line that overexpresses Rex1 and in a Rex1-/- line in which Rex1 expression was restored. These data, taken together, suggest that Rex1 influences differentiation, cell cycle regulation, and cancer progression.

Downregulation of Reproductive Homeobox Gene 6 (Rhox6) Interferes with Male Germ Cell Differentiation.

Homeodomain proteins contain a 60 amino acid DNA binding motif called homeobox that regulates a variety of developmental events such as determination of body segment identity, limb development and organogenesis. Recently, a novel cluster of homeobox genes has been discovered on the X chromosome of the mouse. Because of their selective expression in reproductive organs, they are named Reproductive homeobox genes on the X chromosome (Rhox). Rhox6, a member of the Rhox6 family, is expressed in primordial germ cells (PGCs) in the developing gonad and the placenta, although the biological function of Rhox6 in determination of PGCs and placental cells remains unknown. To investigate the Rhox6 function, we generated male chimeric mice by injection of the gene-trapped embryonic stem cells (ESCs) harboring a hypomorphic mutation in Rhox6 into wild-type blastocysts. Almost all of the male chimeric mice exhibited infertility associated with smaller testes, reduced sperm number and motility and abnormal morphology of the epididymal sperm. Next, to obtain a better understanding of the Rhox6 function in germ cell differentiation, we took advantage of in vitro ESC culture. ESCs can differentiate into PGCs when ESCs are cultured as aggregates called embryoid bodies (EBs) in the medium containing Ascorbic acid, 1-Thioglycerol and Transferrin without the leukemia inhibitory factor. By using a mouse ESC line that expresses the enhanced green fluorescent protein (EGFP) under the promoter of Oct3/4, a central regulator of cellular pluripotency, the presence of PGCs within EBs was monitored in real time by EGFP expression. While this ESC line was induced to differentiate into PGCs, expression of Rhox6 was downregulated by stable expression of the short-hairpin (sh) RNA against the Rhox6 transcripts. The level of Rhox6 knockdown was validated by RT-PCR. As a negative control, a scrambled nucleotide sequence that does not show any match with the mouse genome was used to express shRNA molecules. EBs were generated from multiple independent clones that express either one of the shRNAs, which were isolated by electroporation of the ESC line with each vector, followed by drug selection. We found that 0% of the EBs having the shRNA against the Rhox6 transcripts expressed (n=29; the number of clones used to generate EBs is 17) had EGFP-positive cells, whereas 43% of the EBs having the control shRNA expressed (n=35; the number of clones used to generate EBs is 25) had EGFP-positive cells. To validate differentiation of PGCs, these EBs were pooled according to EGFP expression and used to examine expression of PGC markers by semi-quantitative RT-PCR. Because expression of Rex1, a marker for undifferentiated ESCs, was significantly downregulated in these EBs than in undifferentiated ESCs, EGFP expression detected in the EBs indicates the presence of PGCs, but not the presence of undifferentiated ESCs. Rhox6 as well as other PGC markers including Oct3/4, Rnh2, Piwil2, and Fgls were downregulated in the EBs expressing the shRNA against the Rhox6 transcripts, whereas the EBs expressing the control shRNA with EGFP-positive cells expressed Rhox6 and these PGC markers. Collectively, these in vivo and in vitro studies strongly suggest that downregulation of Rhox6 impairs differentiation of PGCs. This study is supported by the Departmental Startup fund including the USDA Cooperative State Research, Education and Extension Service, Hatch project (ILLU-538-323). (poster)

OCT4A contributes to the stemness and multi-potency of human umbilical cord blood-derived multipotent stem cells (hUCB–MSCs)

The OCT4A gene, a POU homeodomain transcription factor, has been shown to be expressed in embryonic stem cells (ESC) as well as hUCB–MSCs. In this study, the roles played by OCT4A in hUCB–MSCs were determined by stably inhibiting OCT4A with lenti-viral vector-based small hairpin RNA (shRNA). A decreased rate of cell proliferation was observed in OCT4-inhibited hUCB–MSCs. Down-regulation of CCNA2 expression in OCT4-inhibited hUCB–MSCs was confirmed by RT-PCR and real-time RT-PCR analysis in three genetically independent hUCB–MSC clones. Adipogenic differentiation was also suppressed in OCT4-inhibited hUCB–MSCs. The up-regulation of DTX1 and down-regulation of HDAC1, 2, and 4 expressions may be related to this differentiation deformity. The expression of other transcription factors, including SOX2, REX1 and c-MYC, was also affected by OCT4 inhibition in hUCB–MSCs. In conclusion, these finding suggest that OCT4A performs functionally conserved roles in hUCB–MSCs, making its expression biologically important for ex vivo culture of hUCB–MSCs.

Thyrotropin-Independent Induction of Thyroid Endoderm from Embryonic Stem Cells by Activin A

To model the differentiation of thyroid epithelial cells, we examined embryoid bodies derived from undifferentiated murine embryonic stem cells treated with activin A to induce endoderm differentiation, the germ layer from which thyroid cells occur. The resulting endodermal cells were then further exposed to TSH and/or IGF-I for up to 21 d. Oct-4 and REX1 expression, required to sustain stem cell self-renewal and pluripotency, were appropriately down-regulated, whereas GATA-4, and alpha-fetoprotein, both endodermal-specific markers, increased as the embryonic stem cells were exposed to activin A. By d 5 culture, TSH receptor (TSHR) and sodium iodide symporter (NIS) gene and protein expression were markedly induced. Cells isolated by the fluorescence-activated cell sorter simultaneously expressed not only TSHR and NIS proteins but also PAX8 mRNA, an expression pattern unique to thyroid cells and expected in committed thyroid progenitor cells. Such expression continued until d 21 with no influence seen by the addition of TSH or IGF-I. The sequence of gene expression changes observed in these experiments demonstrated the emergence of definitive thyroid endoderm. The activin A induction of thyroid-specific markers, NIS and TSHR, occurred in the absence of TSH stimulation, and, therefore, the emergence of thyroid endoderm in vitro paralleled the emergence of thyroid cells in TSHR-knockout mice. Activin A is clearly a major regulator of thyroid endoderm.

Transcriptional heterogeneity in mouse embryonic stem cells

The embryonic stem (ES) cell is a stem cell derived from early embryos that can indefinitely repeat self-renewing cell division cycles as an undifferentiated cell in vitro and give rise to all specialised cell types in the body. However, manipulating ES cell differentiation in vitro is a challenge due to, at least in part, heterogeneous gene induction. Recent experimental evidence has demonstrated that undifferentiated mouse ES cells maintained in culture exhibit heterogeneous expression of Dppa3, Nanog, Rex1, Pecam1 and Zscan4 as well as genes (Brachyury/T, Rhox6/9 and Twist2) normally expressed in specialised cell types. The Nanog-negative, Rex1-negative or T-positive ES cell subpopulation has a unique differentiation potential. Thus, studying the mechanism that generates ES cell subpopulations will improve manipulation of ES cell fate and help our understanding of the nature of embryonic development.

Identification and characterization of subpopulations in undifferentiated ES cell culture

Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass (ICM) and the epiblast, and have been suggested to be a homogeneous population with characteristics intermediate between them. These cells express Oct3/4 and Rex1 genes, which have been used as markers to indicate the undifferentiated state of ES cells. Whereas Oct3/4 is expressed in totipotent and pluripotent cells in the mouse life cycle, Rex1 expression is restricted to the ICM, and is downregulated in pluripotent cell populations in the later stages, i.e. the epiblast and primitive ectoderm (PrE). To address whether ES cells comprise a homogeneous population equivalent to a certain developmental stage of pluripotent cells or a heterogeneous population composed of cells corresponding to various stages of differentiation, we established knock-in ES cell lines in which genes for fluorescent proteins were inserted into the Rex1 and Oct3/4 gene loci to visualize the expression of these genes. We found that undifferentiated ES cells included at least two different populations, Rex1(+)/Oct3/4(+) cells and Rex1(-)/Oct3/4(+) cells. The Rex1(-)/Oct3/4(+) and Rex1(+)/Oct3/4(+) populations could convert into each other in the presence of LIF. In accordance with our assumption that Rex1(+)/Oct3/4(+) cells and Rex1(-)/Oct3/4(+) cells have characteristics similar to those of ICM and early-PrE cells, Rex1(+)/Oct3/4(+) cells predominantly differentiated into primitive ectoderm and contributed to chimera formation, whereas Rex1(-)/Oct3/4(+) cells differentiated into cells of the somatic lineage more efficiently than non-fractionated ES cells in vitro and showed poor ability to contribute to chimera formation. These results confirmed that undifferentiated ES cell culture contains subpopulations corresponding to ICM, epiblast and PrE.

Presumed pluripotency markers UTF-1 and REX-1 are expressed in human adult testes and germ cell neoplasms

UTF-1 and REX-1/ZFP42 are transcription factors involved in pluripotency. Because of phenotypic similarities between pluripotent embryonic stem cells and testicular germ cell tumours (TGCT) and the derivation of pluripotent cells from testes, we investigated the expression of UTF-1 and REX-1 during human gonadal development and in TGCT. Expression of UTF-1 and REX-1 was studied in 52 specimens from human gonadal development and in 86 samples from TGCT. UTF-1 and REX-1 were expressed throughout male gonadal development. In the mature testis, UTF-1 was expressed in spermatogonia, whereas REX-1 was expressed in meiotic cells and, together with OCT-3/4, in primary oocytes. Both UTF-1 and REX-1 were expressed in testicular carcinoma in situ and in TGCT. Contrarily to REX-1, UTF-1 was expressed in all spermatocytic seminomas. Unlike other pluripotency markers NANOG and OCT-3/4, UTF-1 and REX-1 are expressed throughout human testes development. The expression pattern indicated that UTF-1 plays a possible role in spermatogonial self-renewal, whereas expression of REX-1 in meiotic cells from both testes and ovary indicate a role in meiosis. UFT-1 and REX-1 are expressed in TGCT and the high abundance of UTF-1 in spermatocytic seminomas is consistent with the hypothesis that this tumour type originates from spermatogonia.

FGF stimulation of the Erk1/2 signalling cascade triggers transition of pluripotent embryonic stem cells from self-renewal to lineage commitment

Pluripotent embryonic stem (ES) cells must select between alternative fates of self-replication and lineage commitment during continuous proliferation. Here, we delineate the role of autocrine production of fibroblast growth factor 4 (Fgf4) and associated activation of the Erk1/2 (Mapk3/1) signalling cascade. Fgf4 is the major stimulus activating Erk in mouse ES cells. Interference with FGF or Erk activity using chemical inhibitors or genetic ablations does not impede propagation of undifferentiated ES cells. Instead, such manipulations restrict the ability of ES cells to commit to differentiation. ES cells lacking Fgf4 or treated with FGF receptor inhibitors resist neural and mesodermal induction, and are refractory to BMP-induced non-neural differentiation. Lineage commitment potential of Fgf4-null cells is restored by provision of FGF protein. Thus, FGF enables rather than antagonises the differentiation activity of BMP. The key downstream role of Erk signalling is revealed by examination of Erk2-null ES cells, which fail to undergo either neural or mesodermal differentiation in adherent culture, and retain expression of pluripotency markers Oct4, Nanog and Rex1. These findings establish that Fgf4 stimulation of Erk1/2 is an autoinductive stimulus for naïve ES cells to exit the self-renewal programme. We propose that the Erk cascade directs transition to a state that is responsive to inductive cues for germ layer segregation. Consideration of Erk signalling as a primary trigger that potentiates lineage commitment provides a context for reconciling disparate views on the contribution of FGF and BMP pathways during germ layer specification in vertebrate embryos.