The transcriptional foundation of pluripotency

MicroRNA-137 represses Klf4 and Tbx3 during differentiation of mouse embryonic stem cells

MicroRNA-137 (miR-137) has been shown to play an important role in the differentiation of neural stem cells. Embryonic stem (ES) cells have the potential to differentiate into different cell types including neurons; however, the contribution of miR-137 in the maintenance and differentiation of ES cells remains unknown. Here, we show that miR-137 is mainly expressed in ES cells at the mitotic phase of the cell cycle and highly upregulated during differentiation. We identify that ES cell transcription factors, Klf4 and Tbx3, are downstream targets of miR-137, and we show that endogenous miR-137 represses the 3' untranslated regions of Klf4 and Tbx3. Transfection of ES cells with mature miR-137 RNA duplexes led to a significant reduction in cell proliferation and the expression of Klf4, Tbx3, and other self-renewal genes. Furthermore, we demonstrate that increased miR-137 expression accelerates differentiation of ES cells in vitro. Loss of miR-137 during ES cell differentiation significantly impeded neuronal gene expression and morphogenesis. Taken together, our results suggest that miR-137 regulates ES cell proliferation and differentiation by repressing the expression of downstream targets, including Klf4 and Tbx3.

Toward ovine iPSCs

Abstract Interest in pluripotent livestock stem cells has been with us for over 2 decades, and although much has been claimed over the years, it is only recently that real progress has been achieved. The recent developments have revolved around the ability to reprogram somatic cells to become induced pluripotent stem cells (iPSCs). Progress has been achieved in porcine, bovine, equine, and ovine species; but for each species, the extent of progress is different. I review the position of ovine iPSCs and comment on the two main drivers for this work-to produce "better" cells for nuclear transfer and to develop a good in vitro system to study the early development of ruminants.

Identification and characterization of a nanog homolog in Japanese flounder (Paralichthys olivaceus)

The homeodomain-containing transcription factor nanog plays a key role in maintaining the pluripotency and self-renewal of embryonic stem cells in mammals. Stem cells offered as a significant and effective tool for generation of transgenic animals and preservation of genetic resources. The molecular genetic organization and expression of nanog gene in marine fish have not been reported yet. In this study, we isolated and characterized the flounder nanog gene as a first step towards understanding the mechanism of the plurpotency of fish stem cells and develop a potential molecular marker to identify the stem cells in vivo and in vitro. Phylogenetic, gene structure and chromosome synteny analysis provided the evidence that Po-nanog is homologous to the mammalian nanog gene. Protein sequence comparison showed that flounder Nanog shared low similarity with other vertebrate orthologs except for a conserved homeodomain. Quantitative RT-PCR analysis showed that flounder nanog was maternally expressed, and the transcripts were present from the one-cell stage to the neurula stage with the peaking at blastula stage. Whole mount in situ hybridization analyses demonstrated that the transcripts were present in all blastomeres of the early embryo. Tissue distribution analysis indicated that nanog was detectable only in gonads. Further, the expression was significantly high in ovary than in testis. In situ hybridization revealed that the transcripts were located in the cytoplasm of the oogonia and oocytes in ovary, only in the spermatogonia but no spermatocytes or spermatids in testis. The promoter region was also analyzed to have several basal core promoter elements and transcription factor binding sites. All these results suggest that Po-Nanog may have a conservative function between teleosts and mammals.

Mammalian genes induce partially reprogrammed pluripotent stem cells in non-mammalian vertebrate and invertebrate species

Cells are fundamental units of life, but little is known about evolution of cell states. Induced pluripotent stem cells (iPSCs) are once differentiated cells that have been re-programmed to an embryonic stem cell-like state, providing a powerful platform for biology and medicine. However, they have been limited to a few mammalian species. Here we found that a set of four mammalian transcription factor genes used to generate iPSCs in mouse and humans can induce a partially reprogrammed pluripotent stem cell (PRPSCs) state in vertebrate and invertebrate model organisms, in mammals, birds, fish, and fly, which span 550 million years from a common ancestor. These findings are one of the first to show cross-lineage stem cell-like induction, and to generate pluripotent-like cells for several of these species with in vivo chimeras. We suggest that the stem-cell state may be highly conserved across a wide phylogenetic range.

DOI:http://dx.doi.org/10.7554/eLife.00036.001

Stem cells are ‘pluripotent’—in other words, they have the potential to become many other cell types. This ability makes them extremely valuable for research. They also hold substantial promise for medical applications, since they can be used to replace cells lost or damaged by disease or injury.

Embryos represent a rich source of stem cells; however, obtaining these cells from human embryos raises obvious ethical and practical concerns, and they have also been difficult to isolate from many species. A recent discovery circumvented these issues for humans and several mammalian species commonly studied in the laboratory. This technique can turn cells from adult mammals into ‘induced pluripotent stem cells’, or iPSCs, by switching on four genes. Nevertheless, no analogous method has yet been established to create similar cell populations in non-mammalian organisms, which are also important models for human development and disease.

Now, Rosselló et al. have shown that cells from both invertebrate and non-mammalian vertebrate species—including birds, fish and insects—can be reprogrammed into cells that closely resemble iPSCs. Intriguingly, these cells were created by switching on the same four genes that generate iPSCs in mammals, even though vertebrates and invertebrates are separated by around 550 million years of evolution.

Rosselló et al. used a viral vector that carries the four stem-cell genes (from the mouse) into target cells from the different species. The genetically altered cells developed into iPSC-like cells with many of the characteristics of natural mammalian and bird stem cells. To confirm that the cells were pluripotent, Rossello et al. first showed that the cells could develop into primitive early embryos called embryoid bodies. For the vertebrate species tested, the embryoid bodies contained cells from each of the three main vertebrate embryo cell types. Secondly, iPSC-like cells from two organisms—chicks and zebrafish—formed various mature cell types when injected into developing chick or zebrafish embryos.

These results have two important implications. They suggest that the genetic mechanisms by which cells can be reprogrammed into a stem-like state have been conserved through 550 million years of evolution; additionally, they demonstrate that stem-like cells can be generated from important experimental organisms, and provide an important tool for both biological and biomedical research.

DOI:http://dx.doi.org/10.7554/eLife.00036.002

Identification of active regulatory regions from DNA methylation data

We have recently shown that transcription factor binding leads to defined reduction in DNA methylation, allowing for the identification of active regulatory regions from high-resolution methylomes. Here, we present MethylSeekR, a computational tool to accurately identify such footprints from bisulfite-sequencing data. Applying our method to a large number of published human methylomes, we demonstrate its broad applicability and generalize our previous findings from a neuronal differentiation system to many cell types and tissues. MethylSeekR is available as an R package at www.bioconductor.org.

SOX2 and OCT4 mRNA-expressing cells, detected by molecular beacons, localize to the center of neurospheres during differentiation

Neurospheres are used as in vitro assay to measure the properties of neural stem cells. To investigate the molecular and phenotypic heterogeneity of neurospheres, molecular beacons (MBs) targeted against the stem cell markers OCT4 and SOX2 were designed, and synthesized with a 2'-O-methyl RNA backbone. OCT4 and SOX2 MBs were transfected into human embryonic mesencephalon derived cells, which spontaneously form neurospheres when grown on poly-L-ornitine/fibronectin matrix and medium complemented with bFGF. OCT4 and SOX2 gene expression were tracked in individual cell using the MBs. Quantitative image analysis every day for seven days showed that the OCT4 and SOX2 mRNA-expressing cells clustered in the centre of the neurospheres cultured in differentiation medium. By contrast, cells at the periphery of the differentiating spheres developed neurite outgrowths and expressed the tyrosine hydroxylase protein, indicating terminal differentiation. Neurospheres cultured in growth medium contained OCT4 and SOX2-positive cells distributed throughout the entire sphere, and no differentiating neurones. Gene expression of SOX2 and OCT4 mRNA detected by MBs correlated well with gene and protein expression measured by qRT-PCR and immunostaining, respectively. These experimental data support the theoretical model that stem cells cluster in the centre of neurospheres, and demonstrate the use of MBs for the spatial localization of specific gene-expressing cells within heterogeneous cell populations.

MRAS GTPase is a novel stemness marker that impacts mouse embryonic stem cell plasticity and Xenopus embryonic cell fate

Pluripotent mouse embryonic stem cells (mESCs), maintained in the presence of the leukemia inhibitory factor (LIF) cytokine, provide a powerful model with which to study pluripotency and differentiation programs. Extensive microarray studies on cultured cells have led to the identification of three LIF signatures. Here we focus on muscle ras oncogene homolog (MRAS), which is a small GTPase of the Ras family encoded within the Pluri gene cluster. To characterise the effects of Mras on cell pluripotency and differentiation, we used gain- and loss-of-function strategies in mESCs and in the Xenopus laevis embryo, in which Mras gene structure and protein sequence are conserved. We show that persistent knockdown of Mras in mESCs reduces expression of specific master genes and that MRAS plays a crucial role in the downregulation of OCT4 and NANOG protein levels upon differentiation. In Xenopus, we demonstrate the potential of Mras to modulate cell fate at early steps of development and during neurogenesis. Overexpression of Mras allows gastrula cells to retain responsiveness to fibroblast growth factor (FGF) and activin. Collectively, these results highlight novel conserved and pleiotropic effects of MRAS in stem cells and early steps of development.

Changes in sub-cellular localisation of trophoblast and inner cell mass specific transcription factors during bovine preimplantation development

Background

Preimplantation bovine development is emerging as an attractive experimental model, yet little is known about the mechanisms underlying trophoblast (TE)/inner cell mass (ICM) segregation in cattle. To gain an insight into these processes we have studied protein and mRNA distribution during the crucial stages of bovine development. Protein distribution of lineage specific markers OCT4, NANOG, CDX2 were analysed in 5-cell, 8–16 cell, morula and blastocyst stage embryos. ICM/TE mRNA levels were compared in hatched blastocysts and included: OCT4, NANOG, FN-1, KLF4, c-MYC, REX1, CDX2, KRT-18 and GATA6.

Results

At the mRNA level the observed distribution patterns agree with the mouse model. CDX2 and OCT4 proteins were first detected in 5-cell stage embryos. NANOG appeared at the morula stage and was located in the cytoplasm forming characteristic rings around the nuclei. Changes in sub-cellular localisation of OCT4, NANOG and CDX2 were noted from the 8–16 cell onwards. CDX2 initially co-localised with OCT4, but at the blastocyst stage a clear lineage segregation could be observed. Interestingly, we have observed in a small proportion of embryos (2%) that CDX2 immunolabelling overlapped with mitotic chromosomes.

Conclusions

Cell fate specification in cattle become evident earlier than presently anticipated – around the time of bovine embryonic genome activation. There is an intriguing possibility that for proper lineage determination certain transcription factors (such as CDX2) may need to occupy specific regions of chromatin prior to its activation in the interphase nucleus. Our observation suggests a possible role of CDX2 in the process of epigenetic regulation of embryonic cell fate.

miR-125b regulates the early steps of ESC differentiation through dies1 in a TGF-independent manner

Over the past few years, it has become evident that the distinctive pattern of miRNA expression seen in embryonic stem cells (ESCs) contributes to important signals in the choice of the cell fate. Thus, the identification of miRNAs and their targets, whose expression is linked to a specific step of differentiation, as well as the modulation of these miRNAs, may prove useful in the learning of how ESC potential is regulated. In this context, we have studied the expression profile of miRNAs during neural differentiation of ESCs. We have found that miR-125b is upregulated in the first steps of neural differentiation of ESCs. This miRNA targets the BMP4 co-receptor, Dies1, and, in turn, regulates the balance between BMP4 and Nodal/Activin signaling. The ectopic expression of miR-125b blocks ESC differentiation at the epiblast stage, and this arrest is rescued by restoring the expression of Dies1. Finally, opposite to miR-125a, whose expression is under the control of the BMP4, miR-125b is not directly regulated by Transforming Growth Factor beta (TGFβ) signals. These results highlight a new important role of miR-125b in the regulation of the transition from ESCs to the epiblast stage and add a new level of control on TGFβ signaling in ESCs.

Reprogramming activity of NANOGP8, a NANOG family member widely expressed in cancer

NANOG is a key transcription factor for pluripotency in embryonic stem cells. The analysis of NANOG in human cells is confounded by the presence of multiple and highly similar paralogs. In particular, there are three paralogs encoding full-length proteins, namely, NANOG1, NANOG2 and NANOGP8, and at least eight additional paralogs that do not encode full-length NANOG proteins. Here, we have examined NANOG family expression in human embryonic stem cells (hESCs) and in human cancer cell lines using a multi-NANOG PCR that amplifies the three functional paralogs and most of the non-functional ones. As anticipated, we found that hESCs express large amounts of NANOG1 and, interestingly, they also express NANOG2. In contrast, most human cancer cells tested express NANOGP8 and the non-coding paralogs NANOGP4 and NANOGP5. Notably, in some cancer cell lines, the NANOG protein levels produced by NANOGP8 are comparable to those produced by NANOG1 in pluripotent cells. Finally, we show that NANOGP8 is as active as NANOG1 in the reprogramming of human and murine fibroblasts into induced pluripotent stem cells. These results show that cancer-associated NANOGP8 can contribute to promote de-differentiation and/or cellular plasticity.

Molecular characteristics of malignant ovarian germ cell tumors and comparison with testicular counterparts: implications for pathogenesis

This review focuses on the molecular characteristics and development of rare malignant ovarian germ cell tumors (mOGCTs). We provide an overview of the genomic aberrations assessed by ploidy, cytogenetic banding, and comparative genomic hybridization. We summarize and discuss the transcriptome profiles of mRNA and microRNA (miRNA), and biomarkers (DNA methylation, gene mutation, individual protein expression) for each mOGCT histological subtype. Parallels between the origin of mOGCT and their male counterpart testicular GCT (TGCT) are discussed from the perspective of germ cell development, endocrinological influences, and pathogenesis, as is the GCT origin in patients with disorders of sex development. Integrated molecular profiles of the 3 main histological subtypes, dysgerminoma (DG), yolk sac tumor (YST), and immature teratoma (IT), are presented. DGs show genomic aberrations comparable to TGCT. In contrast, the genome profiles of YST and IT are different both from each other and from DG/TGCT. Differences between DG and YST are underlined by their miRNA/mRNA expression patterns, suggesting preferential involvement of the WNT/β-catenin and TGF-β/bone morphogenetic protein signaling pathways among YSTs. Characteristic protein expression patterns are observed in DG, YST and IT. We propose that mOGCT develop through different developmental pathways, including one that is likely shared with TGCT and involves insufficient sexual differentiation of the germ cell niche. The molecular features of the mOGCTs underline their similarity to pluripotent precursor cells (primordial germ cells, PGCs) and other stem cells. This similarity combined with the process of ovary development, explain why mOGCTs present so early in life, and with greater histological complexity, than most somatic solid tumors.

Connective tissue growth factor activates pluripotency genes and mesenchymal-epithelial transition in head and neck cancer cells

The epithelial-mesenchymal transition (EMT) is a key mechanism in both embryonic development and cancer metastasis. The EMT introduces stem-like properties to cancer cells. However, during somatic cell reprogramming, mesenchymal-epithelial transition (MET), the reverse process of EMT, is a crucial step toward pluripotency. Connective tissue growth factor (CTGF) is a multifunctional secreted protein that acts as either an oncoprotein or a tumor suppressor among different cancers. Here, we show that in head and neck squamous cell carcinoma (HNSCC), CTGF promotes the MET and reduces invasiveness. Moreover, we found that CTGF enhances the stem-like properties of HNSCC cells and increases the expression of multiple pluripotency genes. Mechanistic studies showed that CTGF induces c-Jun expression through αvβ3 integrin and that c-Jun directly activates the transcription of the pluripotency genes NANOG, SOX2, and POU5F1. Knockdown of CTGF in TW2.6 cells was shown to reduce tumor formation and attenuate E-cadherin expression in xenotransplanted tumors. In HNSCC patient samples, CTGF expression was positively correlated with the levels of CDH1, NANOG, SOX2, and POU5F1. Coexpression of CTGF and the pluripotency genes was found to be associated with a worse prognosis. These findings are valuable in elucidating the interplay between epithelial plasticity and stem-like properties during cancer progression and provide useful information for developing a novel classification system and therapeutic strategies for HNSCC.

Reduced Oct4 expression directs a robust pluripotent state with distinct signaling activity and increased enhancer occupancy by Oct4 and Nanog

Embryonic stem cell (ESC) pluripotency is governed by a gene regulatory network centered on the transcription factors Oct4 and Nanog. To date, robust self-renewing ESC states have only been obtained through the chemical inhibition of signaling pathways or enforced transgene expression. Here, we show that ESCs with reduced Oct4 expression resulting from heterozygosity also exhibit a stabilized pluripotent state. Despite having reduced Oct4 expression, Oct4(+/-) ESCs show increased genome-wide binding of Oct4, particularly at pluripotency-associated enhancers, homogeneous expression of pluripotency transcription factors, enhanced self-renewal efficiency, and delayed differentiation kinetics. Cells also exhibit increased Wnt expression, enhanced leukemia inhibitory factor (LIF) sensitivity, and reduced responsiveness to fibroblast growth factor. Although they are able to maintain pluripotency in the absence of bone morphogenetic protein, removal of LIF destabilizes pluripotency. Our findings suggest that cells with a reduced Oct4 concentration range are maintained in a robust pluripotent state and that the wild-type Oct4 concentration range enables effective differentiation.

Differential localization of LGR5 and Nanog in clusters of colon cancer stem cells

One paradigm of cancer development claims that cancer emerges at the niche of tissue stem cells and these cells continue to proliferate in the tumor as cancer stem cells. LGR5, a membrane receptor, was recently found to be a marker of normal colon stem cells in colon polyps and is also expressed in colon cancer stem cells. Nanog, an embryonic stem cell nuclear factor, is expressed in several embryonic tissues, but Nanog expression is not well documented in cancerous stem cells. Our aim was to examine whether both LGR5 and Nanog are expressed in the same clusters of colon stem cells or cancer stem cells, using immunocytochemistry with specific antibodies to each antigen. We analyzed this aspect using paraffin embedded tumor tissue sections obtained from 18 polyps and 36 colon cancer specimens at stages I-IV. Antibodies to LGR5 revealed membrane and cytoplasm immunostaining of scattered labeled cells in normal crypts, with no labeling of Nanog. However, in close proximity to the tumors, staining to LGR5 was much more intensive in the crypts, including that of the epithelial cells. In cancer tissue, positive LGR5 clusters of stem cells were observed mainly in poorly differentiated tumors and in only a few scattered cells in the highly differentiated tumors. In contrast, antibodies to Nanog mainly stained the growing edges of carcinoma cells, leaving the poorly differentiated tumor cells unlabeled, including the clustered stem cells that could be detected even by direct morphological examination. In polyp tissues, scattered labeled cells were immunostained with antibodies to Nanog and to a much lesser extent with antibodies to LGR5. We conclude that expression of LGR5 is probably specific to stem cells of poorly differentiated tumors, whereas Nanog is mainly expressed at the edges of highly differentiated tumors. However, some of the cell layers adjacent to the carcinoma cell layers that still remained undifferentiated, expressed mainly Nanog with only a few cells labeled with antibodies to LGR5. Considering the different sites and pattern of expression in the tumor, our data imply that targeting the clustered stem cells expressing LGR5 in poorly differentiated colon cancer may require different strategies than targeting the stem cells expressing Nanog in the highly differentiated tumors. Alternatively, combined application of specific inhibitory miRNAs to Nanog and to LGR5 expression may assist therapeutically.

Localization of the stem cell markers LGR5 and Nanog in the normal and the cancerous human ovary and their inter-relationship

LGR5 and Nanog were recently characterized as stem cell markers in various embryonic, adult and cancer stem cells. However, there are no data on their precise localization in the normal adult ovary, which may be important for the initial steps of development of ovarian cancer, the most lethal gynecological cancer. We analyzed by immunocytochemistry the precise localization of these markers in normal ovary (11 specimens, age range 43-76), in borderline specimens (12 specimens), and in serous ovarian cancer (12 specimens of stage II) which comprises the vast majority (80%) of all ovarian cancer. Surprisingly, we revealed that both Nanog and LGR5 are clearly localized in the epithelial cells of the normal ovary. However, in 5 of 12 ovaries there was no labeling at all, while in 3 ovaries staining of Nanog was more prominent with only weak labeling of LGR5. In addition, we found in 3 of 11 ovaries clear labeling in foci of both LGR5 and Nanog antibodies, with partial overlapping. Occasionally, we also found in the stroma foci labeled by either Nanog or LGR5 antibodies. In general, the stroma area of tissue sections labeled with LGR5 was much greater than that labeled with Nanog. In borderline tumors a significant portion of the specimens (7 of 12) was labeled exclusively with Nanog and not with LGR5. In ovarian carcinomas almost 100% of the cells were exclusively labeled only with Nanog (6 of 12 of the specimens) with no labeling of LGR5. These data may suggest the potential of ovaries from postmenopausal women, which express Nanog, to undergo transformation, since Nanog was shown to be oncogenic. We conclude that Nanog, which probably plays an important role in ovarian embryonic development, may be partially silenced in fertile and post-menopausal women, but is re-expressed in ovarian cancer, probably by epigenetic activation of Nanog gene expression. Expression of Nanog and LGR5 in normal ovaries and in borderline tumors may assist in the early detection and improved prognosis of ovarian cancer. Moreover, targeting of Nanog by inhibitory miRNA or other means may assist in treating this disease.

Differential expression of ID4 and its association with TP53 mutation, SOX2, SOX4 and OCT-4 expression levels

Inhibitor of DNA Binding 4 (ID4) is a member of the helix-loop-helix ID family of transcription factors, mostly present in the central nervous system during embryonic development, that has been associated with TP53 mutation and activation of SOX2. Along with other transcription factors, ID4 has been implicated in the tumorigenic process of astrocytomas, contributing to cell dedifferentiation, proliferation and chemoresistance. In this study, we aimed to characterize the ID4 expression pattern in human diffusely infiltrative astrocytomas of World Health Organization (WHO) grades II to IV of malignancy (AGII-AGIV); to correlate its expression level to that of SOX2, SOX4, OCT-4 and NANOG, along with TP53 mutational status; and to correlate the results with the clinical end-point of overall survival among glioblastoma patients. Quantitative real time PCR (qRT-PCR) was performed in 130 samples of astrocytomas for relative expression, showing up-regulation of all transcription factors in tumor cases. Positive correlation was found when comparing ID4 relative expression of infiltrative astrocytomas with SOX2 (r = 0.50; p<0.005), SOX4 (r = 0.43; p<0.005) and OCT-4 (r = 0.39; p<0.05). The results from TP53 coding exon analysis allowed comparisons between wild-type and mutated status only in AGII cases, demonstrating significantly higher levels of ID4, SOX2 and SOX4 in mutated cases (p<0.05). This pattern was maintained in secondary GBM and further confirmed by immunohistochemistry, suggesting a role for ID4, SOX2 and SOX4 in early astrocytoma tumorigenesis. Combined hyperexpression of ID4, SOX4 and OCT-4 conferred a much lower (6 months) median survival than did hypoexpression (18 months). Because both ID4 alone and a complex of SOX4 and OCT-4 activate SOX2 transcription, it is possible that multiple activation of SOX2 impair the prognosis of GBM patients. These observational results of associated expression of ID4 with SOX4 and OCT-4 may be used as a predictive factor of prognosis upon further confirmation in a larger GBM series.

Willin, an upstream component of the hippo signaling pathway, orchestrates mammalian peripheral nerve fibroblasts

Willin/FRMD6 was first identified in the rat sciatic nerve, which is composed of neurons, Schwann cells, and fibroblasts. Willin is an upstream component of the Hippo signaling pathway, which results in the inactivation of the transcriptional co-activator YAP through Ser127 phosphorylation. This in turn suppresses the expression of genes involved in cell growth, proliferation and cancer development ensuring the control of organ size, cell contact inhibition and apoptosis. Here we show that in the mammalian sciatic nerve, Willin is predominantly expressed in fibroblasts and that Willin expression activates the Hippo signaling cascade and induces YAP translocation from the nucleus to the cytoplasm. In addition within these cells, although it inhibits cellular proliferation, Willin expression induces a quicker directional migration towards scratch closure and an increased expression of factors linked to nerve regeneration. These results show that Willin modulates sciatic nerve fibroblast activity indicating that Willin may have a potential role in the regeneration of the peripheral nervous system.

Immunohistochemical localization and characterization of putative mesenchymal stem cell markers in the retinal capillary network of rodents

Perivascular cells of microvascular niches are the prime candidates for being a reservoire of mesenchymal stem cell (MSC)-like cells in many tissues and organs that could serve as a potential source of cells and a target of novel cell-based therapeutic approaches. In the present study, by utilising typical markers of pericytes (neuronal-glial antigen 2, NG2, a chondroitin sulphate proteoglycan) and those of MSCs (CD146 and CD105) and primitive pluripotent cells (sex-determining region Y-box 2, Sox2), the phenotypic traits and the distribution of murine and rat retinal perivascular cells were investigated in situ. Our findings indicate that retinal microvessels of juvenile rodents are highly covered by NG2-positive branching processes of pericytic (perivascular) cells that are less prominent in mature capillary networks of the adult retina. In the adult rodent retinal vascular bed, NG2 labeling is mainly confined to membranes of the cell body resulting in a pearl-chain-like distribution along the vessels. Retinal pericytes, which were identified by their morphology and NG2 expression, simultaneously express CD146. Furthermore, CD146-positive cells located at small arteriole-to-capillary branching points appear more intensely stained than elsewhere. Evidence for a differential expression of the two markers around capillaries that would hint at a clonal heterogeneity among pericytic cells, however, is lacking. In contrast, the expression of CD105 is exclusively restricted to vascular endothelial cells and Sox2 is detected neither in perivascular nor in endothelial cells. In dissociated retinal cultures, however, simultaneous expression of NG2 and CD105 was observed. Collectively, our data indicate that vascular wall resident retinal pericytes share some phenotypic features (i.e. CD146 expression) with archetypal MSCs, which is even more striking in dissociated retinal cultures (i.e. CD105 expression). These findings might have implications for the treatment of retinal pathologies.

Forced expression of OCT4 influences the expression of pluripotent genes in human mesenchymal stem cells and fibroblasts

Genetic reprogramming of adult cells to generate induced pluripotent stem (iPS) cells is a new and important step in sidestepping some of the ethical issues and risks involved in the use of embryonic stem cells. iPS cells can be generated by introduction of transcription factors, such as OCT4, SOX2, KLF4, and CMYC. iPS cells resemble embryonic stem cells in their properties and differentiation potential. The mechanisms that lead to induced pluripotency and the effect of each transcription factor are not completely understood. We performed a critical evaluation of the effect of overexpressing OCT4 in mesenchymal stem cells and fibroblasts and found that OCT4 can activate the expression of other stemness genes, such as SOX2, NANOG, CMYC, FOXD3, KLF4, and βCATENIN, which are not normally or are very weakly expressed in mesenchymal stem cells. Transient expression of OCT4 was also performed to evaluate whether these genes are affected by its overexpression in the first 48 h. Transfected fibroblast cells expressed around 275-fold more OCT4 than non-transfected cells. In transient expression, in which cells were analyzed after 48 h, we detected only the up-regulation of FOXD3, SOX2, and KLF4 genes, suggesting that these genes are the earlier targets of OCT4 in this cellular type. We conclude that forced expression of OCT4 can alter cell status and activate the pluripotent network. Knowledge gained through study of these systems may help us to understand the kinetics and mechanism of cell reprogramming.

Generation of embryonic stem cell lines from immature rabbit ovarian follicles

In mammalian ovaries, many immature follicles remain after the dominant follicles undergo ovulation. Here we report the successful production of rabbit embryonic stem cells (ESCs) from oocytes produced by in vitro culture of immature follicles and subsequent in vitro maturation treatment. In total, we obtained 53 blastocysts from oocytes that received intracytoplasmic sperm injection followed by in vitro culture. Although only weak expression of POU5f1 was observed in the inner cell masses of in-vitro-cultured follicle-derived embryos, repeated careful cloning enabled establishment of 3 stable ESC lines. These ESC lines displayed the morphological characteristics of primed pluripotent stem cells. The ESC lines also expressed the pluripotent markers Nanog, POU5f1, and Sox2. Further, these ESCs could be differentiated into each of the 3 different germ layers both in vitro and in vivo. These results demonstrate that immature follicles from rabbits can be used to generate ESCs. Moreover, the use of rabbit oocytes as a cell source provides an experimental system that closely matches human reproductive and stem cell physiology.

Tcf7l1 prepares epiblast cells in the gastrulating mouse embryo for lineage specification

The core gene regulatory network (GRN) in embryonic stem cells (ESCs) integrates activities of the pro-self-renewal factors Oct4 (Pou5f1), Sox2 and Nanog with that of an inhibitor of self-renewal, Tcf7l1 (Tcf3). The inhibitor function of Tcf7l1 causes dependence on extracellular Wnt/β-catenin signaling activity, making its embryonic role within the ESC GRN unclear. By analyzing intact mouse embryos, we demonstrate that the function of Tcf7l1 is necessary for specification of cell lineages to occur concomitantly with the elaboration of a three-dimensional body plan during gastrulation. In Tcf7l1(-/-) embryos, specification of mesoderm is delayed, effectively uncoupling it from the induction of the primitive streak. Tcf7l1 repressor activity is necessary for a rapid switch in the response of pluripotent cells to Wnt/β-catenin stimulation, from one of self-renewal to a mesoderm specification response. These results identify Tcf7l1 as a unique factor that is necessary in pluripotent cells to prepare them for lineage specification. We suggest that the role of Tcf7l1 in mammals is to inhibit the GRN to ensure the coordination of lineage specification with the dynamic cellular events occurring during gastrulation.

Esrrb is a direct Nanog target gene that can substitute for Nanog function in pluripotent cells

Embryonic stem cell (ESC) self-renewal efficiency is determined by the level of Nanog expression. However, the mechanisms by which Nanog functions remain unclear, and in particular, direct Nanog target genes are uncharacterized. Here we investigate ESCs expressing different Nanog levels and Nanog^−/− cells with distinct functionally inducible Nanog proteins to identify Nanog-responsive genes. Surprisingly, these constitute a minor fraction of genes that Nanog binds. Prominent among Nanog-reponsive genes is Estrogen-related receptor b (Esrrb). Nanog binds directly to Esrrb, enhances binding of RNAPolII, and stimulates Esrrb transcription. Overexpression of Esrrb in ESCs maintains cytokine-independent self-renewal and pluripotency. Remarkably, this activity is retained in Nanog^−/− ESCs. Moreover, Esrrb can reprogram Nanog^−/− EpiSCs and can rescue stalled reprogramming in Nanog^−/− pre-iPSCs. Finally, Esrrb deletion abolishes the defining ability of Nanog to confer LIF-independent ESC self-renewal. These findings are consistent with the functional placement of Esrrb downstream of Nanog.

A small molecule (pluripotin) as a tool for studying cancer stem cell biology: proof of concept

BACKGROUND

Cancer stem cells (CSC) are thought to be responsible for tumor maintenance and heterogeneity. Bona fide CSC purified from tumor biopsies are limited in supply and this hampers study of CSC biology. Furthermore, purified stem-like CSC subpopulations from existing tumor lines are unstable in culture. Finding a means to overcome these technical challenges would be a useful goal. In a first effort towards this, we examined whether a chemical probe that promotes survival of murine embryonic stem cells without added exogenous factors can alter functional characteristics in extant tumor lines in a fashion consistent with a CSC phenotype.

METHODOLOGY/PRINCIPAL FINDINGS

The seven tumor lines of the NCI60 colon subpanel were exposed to SC-1 (pluripotin), a dual kinase and GTPase inhibitor that promotes self-renewal, and then examined for tumorigenicity under limiting dilution conditions and clonogenic activity in soft agar. A statistically significant increase in tumor formation following SC-1 treatment was observed (p<0.04). Cloning efficiencies and expression of putative CSC surface antigens (CD133 and CD44) were also increased. SC-1 treatment led to sphere formation in some colon tumor lines. Finally, SC-1 inhibited in vitro kinase activity of RSK2, and another RSK2 inhibitor increased colony formation implicating a role for this kinase in eliciting a CSC phenotype.

CONCLUSIONS/SIGNIFICANCE

These findings validate a proof of concept study exposure of extant tumor lines to a small molecule may provide a tractable in vitro model for understanding CSC biology.

SOX2 co-occupies distal enhancer elements with distinct POU factors in ESCs and NPCs to specify cell state

SOX2 is a master regulator of both pluripotent embryonic stem cells (ESCs) and multipotent neural progenitor cells (NPCs); however, we currently lack a detailed understanding of how SOX2 controls these distinct stem cell populations. Here we show by genome-wide analysis that, while SOX2 bound to a distinct set of gene promoters in ESCs and NPCs, the majority of regions coincided with unique distal enhancer elements, important cis-acting regulators of tissue-specific gene expression programs. Notably, SOX2 bound the same consensus DNA motif in both cell types, suggesting that additional factors contribute to target specificity. We found that, similar to its association with OCT4 (Pou5f1) in ESCs, the related POU family member BRN2 (Pou3f2) co-occupied a large set of putative distal enhancers with SOX2 in NPCs. Forced expression of BRN2 in ESCs led to functional recruitment of SOX2 to a subset of NPC-specific targets and to precocious differentiation toward a neural-like state. Further analysis of the bound sequences revealed differences in the distances of SOX and POU peaks in the two cell types and identified motifs for additional transcription factors. Together, these data suggest that SOX2 controls a larger network of genes than previously anticipated through binding of distal enhancers and that transitions in POU partner factors may control tissue-specific transcriptional programs. Our findings have important implications for understanding lineage specification and somatic cell reprogramming, where SOX2, OCT4, and BRN2 have been shown to be key factors.

In mammals, a few thousand transcription factors regulate the differential expression of more than 20,000 genes to specify ∼200 functionally distinct cell types during development. How this is accomplished has been a major focus of biology. Transcription factors bind non-coding DNA regulatory elements, including proximal promoters and distal enhancers, to control gene expression. Emerging evidence indicates that transcription factor binding at distal enhancers plays an important role in the establishment of tissue-specific gene expression programs during development. Further, combinatorial binding among groups of transcription factors can further increase the diversity and specificity of regulatory modules. Here, we report the genome-wide binding profile of the HMG-box containing transcription factor SOX2 in mouse embryonic stem cells (ESCs) and neural progenitor cells (NPCs), and we show that SOX2 occupied a distinct set of binding sites with POU homeodomain family members, OCT4 in ESCs and BRN2 in NPCs. Thus, transitions in SOX2-POU partners may control tissue-specific gene networks. Ultimately, a global analysis detailing the combinatorial binding of transcription factors across all tissues is critical to understand cell fate specification in the context of the complex mammalian genome.

Sox2 is an androgen receptor-repressed gene that promotes castration-resistant prostate cancer

Despite advances in detection and therapy, castration-resistant prostate cancer continues to be a major clinical problem. The aberrant activity of stem cell pathways, and their regulation by the Androgen Receptor (AR), has the potential to provide insight into novel mechanisms and pathways to prevent and treat advanced, castrate-resistant prostate cancers. To this end, we investigated the role of the embryonic stem cell regulator Sox2 [SRY (sex determining region Y)-box 2] in normal and malignant prostate epithelial cells. In the normal prostate, Sox2 is expressed in a portion of basal epithelial cells. Prostate tumors were either Sox2-positive or Sox2-negative, with the percentage of Sox2-positive tumors increasing with Gleason Score and metastases. In the castration-resistant prostate cancer cell line CWR-R1, endogenous expression of Sox2 was repressed by AR signaling, and AR chromatin-IP shows that AR binds the enhancer element within the Sox2 promoter. Likewise, in normal prostate epithelial cells and human embryonic stem cells, increased AR signaling also decreases Sox2 expression. Resistance to the anti-androgen MDV3100 results in a marked increase in Sox2 expression within three prostate cancer cell lines, and in the castration-sensitive LAPC-4 prostate cancer cell line ectopic expression of Sox2 was sufficient to promote castration-resistant tumor formation. Loss of Sox2 expression in the castration-resistant CWR-R1 prostate cancer cell line inhibited cell growth. Up-regulation of Sox2 was not associated with increased CD133 expression but was associated with increased FGF5 (Fibroblast Growth Factor 5) expression. These data propose a model of elevated Sox2 expression due to loss of AR-mediated repression during castration, and consequent castration-resistance via mechanisms not involving induction of canonical embryonic stem cell pathways.

Induced pluripotent stem cells in reproductive medicine

Despite recent advances in reproductive medicine, there are still no effective treatments for severe infertility caused by congenital absence of germ cells or gonadotoxic treatments during prepubertal childhood. However, the development of technologies for germ cell formation from stem cells in vitro, induction of pluripotency from somatic cells, and production of patient-specific pluripotent stem cells may provide new solutions for treating these severe fertility problems. It may be possible to produce germ cells in vitro from our own somatic cells that can be used to restore fertility. In addition, these technologies may also bring about novel therapies by helping to elucidate the mechanisms of human germ cell development. In this review, we describe the current approaches for obtaining germ cells from pluripotent stem cells, and provide basic information about induction of pluripotency and germ cell development.

Involvement of histone demethylase LSD1 in short-time-scale gene expression changes during cell cycle progression in embryonic stem cells

The histone demethylase LSD1, a component of the CoREST (corepressor for element 1-silencing transcription factor) corepressor complex, plays an important role in the downregulation of gene expression during development. However, the activities of LSD1 in mediating short-time-scale gene expression changes have not been well understood. To reveal the mechanisms underlying these two distinct functions of LSD1, we performed genome-wide mapping and cellular localization studies of LSD1 and its dimethylated histone 3 lysine 4 (substrate H3K4me2) in mouse embryonic stem cells (ES cells). Our results showed an extensive overlap between the LSD1 and H3K4me2 genomic regions and a correlation between the genomic levels of LSD1/H3K4me2 and gene expression, including many highly expressed ES cell genes. LSD1 is recruited to the chromatin of cells in the G(1)/S/G(2) phases and is displaced from the chromatin of M-phase cells, suggesting that LSD1 or H3K4me2 alternatively occupies LSD1 genomic regions during cell cycle progression. LSD1 knockdown by RNA interference or its displacement from the chromatin by antineoplastic agents caused an increase in the levels of a subset of LSD1 target genes. Taken together, these results suggest that cell cycle-dependent association and dissociation of LSD1 with chromatin mediates short-time-scale gene expression changes during embryonic stem cell cycle progression.

Defining stem cell types: understanding the therapeutic potential of ESCs, ASCs, and iPS cells

Embryonic, adult, artificially reprogrammed, and cancer…- there are various types of cells associated with stemness. Do they have something fundamental in common? Are we applying a common name to very different entities? In this review, we will revisit the characteristics that define 'pluripotency', the main property of stem cells (SCs). For each main type of physiological (embryonic and adult) or synthetic (induced pluripotent) SCs, markers and functional behavior in vitro and in vivo will be described. We will review the pioneering work that has led to obtaining human SC lines, together with the problems that have arisen, both in a biological context (DNA alterations, heterogeneity, tumors, and immunogenicity) and with regard to ethical concerns. Such problems have led to proposals for new operative procedures for growing human SCs of sufficiently high quality for use as models of disease and in human therapy. Finally, we will review the data from the first clinical trials to use various types of SCs.

Ncoa3 functions as an essential Esrrb coactivator to sustain embryonic stem cell self-renewal and reprogramming

Embryonic stem cell (ESC) pluripotency depends on a well-characterized gene regulatory network centered on Oct4, Sox2, and Nanog. In contrast, little is known about the identity of the key coregulators and the mechanisms by which they may potentiate transcription in ESCs. Alongside core transcription factors, the orphan nuclear receptor Esrrb (estrogen-related receptor β) is vital for the maintenance of ESC identity and furthermore is uniquely associated with the basal transcription machinery. Here, we show that Ncoa3, an essential coactivator, is required to mediate Esrrb function in ESCs. Ncoa3 interacts with Esrrb via its ligand-binding domain and bridges Esrrb to RNA polymerase II complexes. Functionally, Ncoa3 is critical for both the induction and maintenance of pluripotency. Through chromatin immunoprecipitation (ChIP) sequencing and microarray experiments, we further demonstrate that Ncoa3 shares overlapping gene regulatory functions with Esrrb and cooperates genome-wide with the Oct4-Sox2-Nanog circuitry at active enhancers to up-regulate genes involved in self-renewal and pluripotency. We propose an integrated model of transcriptional and coactivator control, mediated by Ncoa3, for the maintenance of ESC self-renewal and somatic cell reprogramming.

Stem cells for reprogramming: could hUMSCs be a better choice?

Human umbilical cord mesenchymal stem cells (hUMSC) are primitive multipotent cells capable of differentiating into cells of different lineages. They can be an alternative source of pluripotent cells since they are ethically and regulatory approved, are easily obtained and have low immunogenicity compared to embryonic stem cells which are dogged with numerous controversies. hUMSC can be a great source for cell and transplantation therapy.

Sorafenib inhibits growth, migration, and angiogenic potential of ectopic endometrial mesenchymal stem cells derived from patients with endometriosis

OBJECTIVE

To characterize the proliferation, migration, and angiogenic properties of mesenchymal stem cells (MSC) from ectopic and eutopic endometrial tissue and to investigate the effect of the tyrosine kinase inhibitor sorafenib.

DESIGN

In vitro studies.

SETTING

University hospital and research center.

PATIENT(S)

Patients receiving surgical treatment of endometriosis (n = 4) and control patients without endometriosis (n = 2) undergoing surgery for benign gynecologic diseases.

INTERVENTION(S)

Mesenchymal stem cell lines were isolated from ectopic and eutopic endometrial tissue, and sorafenib was administered to them.

MAIN OUTCOME MEASURE(S)

Proliferation, migration, invasion of endometrial MSC, and expression of ezrin, vascular endothelial growth factor, and hypoxia-inducible factor-1α (HIF-1α) were measured.

RESULT(S)

Ectopic endometrial MSC from patients with endometriosis showed a higher proliferation, migration, and angiogenic ability than eutopic MSC from the same patient or control MSC from patients without endometriosis. Sorafenib reduced the proliferation, motility, ezrin phosphorylation, vascular endothelial growth factor release, and HIF-1α expression of ectopic MSC.

CONCLUSION(S)

The increased proliferative, migratory, and angiogenic phenotype of ectopic MSC may be reverted by treatment with sorafenib. Targeting of the MSC population involved in sustaining the ectopic lesions might be useful in eradicating endometriotic implants.

On the role of Wnt/β-catenin signaling in stem cells

BACKGROUND

Stem cells are mainly characterized by two properties: self-renewal and the potency to differentiate into diverse cell types. These processes are regulated by different growth factors including members of the Wnt protein family. Wnt proteins are secreted glycoproteins that can activate different intracellular signaling pathways.

SCOPE OF REVIEW

Here we summarize our current knowledge on the role of Wnt/β-catenin signaling with respect to these two main features of stem cells.

MAJOR CONCLUSIONS

A particular focus is given on the function of Wnt signaling in embryonic stem cells. Wnt signaling can also improve reprogramming of somatic cells towards iPS cells highlighting the importance of this pathway for self-renewal and pluripotency. As an example for the role of Wnt signaling in adult stem cell behavior, we furthermore focus on intestinal stem cells located in the crypts of the small intestine.

GENERAL SIGNIFICANCE

A broad knowledge about stem cell properties and the influence of intrinsic and extrinsic factors on these processes is a requirement for the use of these cells in regenerative medicine in the future or to understand cancer development in the adult. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

ZFX controls the self-renewal of human embryonic stem cells

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) offer great promise in regenerative medicine and disease modeling due to their unlimited self-renewal and broad differentiation capacity. There is evidence that the growth properties and critical signaling pathways differ between murine and human ESCs; therefore, it is essential to perform functional studies to test the putatively conserved mechanisms of pluripotent stem cell self-renewal between species. Previously, we identified the transcription factor Zfx as a key regulator of self-renewal in murine ESCs. Here we extend those findings to human ESCs. ZFX knockdown in hESCs hindered clonal growth and decreased colony size after serial replating. ZFX overexpression enhanced clone formation in the presence of Y-27632, increased colony size at low density and decreased expression of differentiation-related genes in human ESCs. ZFX-overexpressing hESCs resisted spontaneous differentiation but could be directed to differentiate into endodermal and neural cell fates when provided with the appropriate cues. Thus, ZFX acts as a molecular rheostat regulating the balance between self-renewal and differentiation in hESCs, revealing the close evolutionary conservation of the self-renewal mechanisms in murine and human ESCs.

[DNA-binding profiles of mammalian transcription factors]

The differential gene expression is the molecular base of development and responses to stimuli of organisms. Transcription factors (TFs) play important regulatory roles in this kind of differential gene expression. Therefore, to elucidate how these TFs regulate the complex differential gene expression, it is necessary to identify all target genes of them and construct the gene transcription regulatory network controlled by them. DNA binding is a key step for TFs regulating gene transcription. Therefore, in order to identify their target genes, it is indispensable to identify all possible DNA sequences that can be recognized and bound by TFs at the molecular level of their interactions with DNA, i.e., construction of the DNA-binding profiles of TFs. In recent years, along with the development of DNA microarray and high-throughput DNA sequencing techniques, there appeared some revolutionary new techniques for constructing DNA-binding profiles of TFs, which greatly promotes studies in this field. These techniques include ChIP-chip and ChIP-Seq for constructing in vivo DNA-binding profiles of TFs, dsDNA microarray, SELEX-SAGE, Bind-n-Seq, MMP-SELEX, EMSA-Seq, and HiTS-FLIP for constructing in vitro DNA-binding profiles of TFs. This paper reviewed these techniques.

Pluripotency in the embryo and in culture

Specific cells within the early mammalian embryo have the capacity to generate all somatic lineages plus the germline. This property of pluripotency is confined to the epiblast, a transient tissue that persists for only a few days. In vitro, however, pluripotency can be maintained indefinitely through derivation of stem cell lines. Pluripotent stem cells established from the newly formed epiblast are known as embryonic stem cells (ESCs), whereas those generated from later stages are called postimplantation epiblast stem cells (EpiSCs). These different classes of pluripotent stem cell have distinct culture requirements and gene expression programs, likely reflecting the dynamic development of the epiblast in the embryo. In this chapter we review current understanding of how the epiblast forms and relate this to the properties of derivative stem cells. We discuss whether ESCs and EpiSCs are true counterparts of different phases of epiblast development or are culture-generated phenomena. We also consider the proposition that early epiblast cells and ESCs may represent a naïve ground state without any prespecification of lineage choice, whereas later epiblasts and EpiSCs may be primed in favor of particular fates.

Understanding cardiovascular disease: a journey through the genome (and what we found there)

Cardiovascular disease (CVD) is a major cause of mortality and hospitalization worldwide. Several risk factors have been identified that are strongly associated with the development of CVD. However, these explain only a fraction of cases, and the focus of research into the causes underlying the unexplained risk has shifted first to genetics and more recently to genomics. A genetic contribution to CVD has long been recognized; however, with the exception of certain conditions that show Mendelian inheritance, it has proved more challenging than anticipated to identify the precise genomic components responsible for the development of CVD. Genome-wide association studies (GWAS) have provided information about specific genetic variations associated with disease, but these are only now beginning to reveal the underlying molecular mechanisms. To fully understand the biological implications of these associations, we need to relate them to the exquisite, multilayered regulation of protein expression, which includes chromatin remodeling, regulatory elements, microRNAs and alternative splicing. Understanding how the information contained in the DNA relates to the operation of these regulatory layers will allow us not only to better predict the development of CVD but also to develop more effective therapies.

The developmental dismantling of pluripotency is reversed by ectopic Oct4 expression

The transcription factors Nanog and Oct4 regulate pluripotency in the pre-implantation epiblast and in derivative embryonic stem cells. During post-implantation development, the precise timing and mechanism of the loss of pluripotency is unknown. Here, we show that in the mouse, pluripotency is extinguished at the onset of somitogenesis, coincident with reduced expression and chromatin accessibility of Oct4 and Nanog regulatory regions. Prior to somitogenesis expression of both Nanog and Oct4 is regionalized. We show that pluripotency tracks the in vivo level of Oct4 and not Nanog by assessing the ability to reactivate or maintain Nanog expression in cell culture. Enforced Oct4 expression in somitogenesis-stage tissue provokes rapid reopening of Oct4 and Nanog chromatin, Nanog re-expression and resuscitates moribund pluripotency. Our data suggest that decreasing Oct4 expression is converted to a sudden drop in competence to maintain pluripotency gene regulatory network activity that is subsequently stabilized by epigenetic locks.

Efficient stem cell isolation from under vacuum preserved tissue samples

Different approaches for the isolation of stem/progenitor cells have been reported, including stem cell selection in stringent culture conditions. We evaluated the possibility of isolating human progenitor cells from surgical specimens preserved by under vacuum sealing and cooling, a clinical practice approached by several hospitals as alternative to formalin. Renal tissue samples (n = 20) maintained under vacuum from 6 to 48 h at 4°C were used to isolate human renal CD133⁺ progenitor cells. We obtained CD133⁺ progenitors from unsorted cells derived from disaggregated tissues from each sample. Phenotypic characterization as well as in vitro and in vivo differentiation of the obtained CD133⁺ lines showed results comparable with sorted CD133⁺ cells obtained from fresh tissue. These results indicate that the process of sealing under vacuum and cooling appears as a suitable tissue treatment to isolate hypoxia resistant cells, such as human stem/progenitor cells, and that this procedure can be exploited to render the extraction of stem cells from human samples more practical and feasible.

MINIYO and transcriptional elongation: lifting the roadblock to differentiation

Inhibiting transcriptional elongation is a recurrent mechanism to keep cells in an undifferentiated, pluripotent state in metazoans. It remains, however, unclear whether lifting the barrier to transcriptional elongation acts as the switch to initiate differentiation in those organisms. Recent results suggest that such a mechanism for turning on differentiation does exist in plants. We argue that targeting the elongation phase of transcription may be a solution adopted widely in evolution to allow for the global transcriptional changes needed in cellular differentiation.

LIF-dependent signaling: new pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.

Transgenic mouse analysis of Sry expression during the pre- and peri-implantation stage

BACKGROUND

The SRY/Sry gene is expressed in pre-Sertoli cells of the male genital ridge and functions as the mammalian testis determining factor (TDF). In addition, expression of SRY/Sry outside the genital ridge has been reported, including preimplantation embryos, although the functional significance of this is not well understood.

RESULTS

Using Cre-mediated lineage studies and transgenic reporter mouse models, we now show that promoter sequences of human, pig and mouse SRY drive robust reporter gene expression in epiblast cells of peri-implantation embryos between embryonic day (E) 4.5 and E6.5. Analysis of endogenous Sry expression revealed that linear transcripts are produced by means of multiple polyadenylation sites in E4.5 embryos. Within the epiblast, SRY reporter expression mimics the expression seen using a Gata4 reporter model, but is dissimilar to that seen using an Oct4 reporter model. In addition, we report that overexpression of mouse Sry in embryonic stem cells leads to down-regulation of the core pluripotency markers Sox2 and Nanog.

CONCLUSION

We propose that SRY/Sry may function as a male-specific maturation factor in the peri-implantation mammalian embryo, providing a genetic mechanism to help explain the observation that male embryos are developmentally more advanced compared with female embryos, and suggesting a role for SRY beyond that of TDF.