Context-dependent wiring of Sox2 regulatory networks for self-renewal of embryonic and trophoblast stem cells

Epigenetic memory of the first cell fate decision prevents complete ES cell reprogramming into trophoblast

Embryonic (ES) and trophoblast (TS) stem cells reflect the first, irrevocable cell fate decision in development that is reinforced by distinct epigenetic lineage barriers. Nonetheless, ES cells can seemingly acquire TS-like characteristics upon manipulation of lineage-determining transcription factors or activation of the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway. Here we have interrogated the progression of reprogramming in ES cell models with regulatable Oct4 and Cdx2 transgenes or conditional Erk1/2 activation. Although trans-differentiation into TS-like cells is initiated, lineage conversion remains incomplete in all models, underpinned by the failure to demethylate a small group of TS cell genes. Forced expression of these non-reprogrammed genes improves trans-differentiation efficiency, but still fails to confer a stable TS cell phenotype. Thus, even ES cells in ground-state pluripotency cannot fully overcome the boundaries that separate the first cell lineages but retain an epigenetic memory of their ES cell origin.

HIPPO pathway members restrict SOX2 to the inner cell mass where it promotes ICM fates in the mouse blastocyst

Pluripotent epiblast (EPI) cells, present in the inner cell mass (ICM) of the mouse blastocyst, are progenitors of both embryonic stem (ES) cells and the fetus. Discovering how pluripotency genes regulate cell fate decisions in the blastocyst provides a valuable way to understand how pluripotency is normally established. EPI cells are specified by two consecutive cell fate decisions. The first decision segregates ICM from trophectoderm (TE), an extraembryonic cell type. The second decision subdivides ICM into EPI and primitive endoderm (PE), another extraembryonic cell type. Here, we investigate the roles and regulation of the pluripotency gene Sox2 during blastocyst formation. First, we investigate the regulation of Sox2 patterning and show that SOX2 is restricted to ICM progenitors prior to blastocyst formation by members of the HIPPO pathway, independent of CDX2, the TE transcription factor that restricts Oct4 and Nanog to the ICM. Second, we investigate the requirement for Sox2 in cell fate specification during blastocyst formation. We show that neither maternal (M) nor zygotic (Z) Sox2 is required for blastocyst formation, nor for initial expression of the pluripotency genes Oct4 or Nanog in the ICM. Rather, Z Sox2 initially promotes development of the primitive endoderm (PE) non cell-autonomously via FGF4, and then later maintains expression of pluripotency genes in the ICM. The significance of these observations is that 1) ICM and TE genes are spatially patterned in parallel prior to blastocyst formation and 2) both the roles and regulation of Sox2 in the blastocyst are unique compared to other pluripotency factors such as Oct4 or Nanog.

Pluripotent stem cells can give rise to any cell type in the body, making them an attractive tool for regenerative medicine. Pluripotent stem cells can be derived from the mammalian embryo at the blastocyst stage or they can be created from mature adult cells by reprogramming. During reprogramming, SOX2 helps establish pluripotency, but it is not clear how SOX2 establishes pluripotency in the blastocyst. We evaluated where SOX2 is present, how SOX2 is regulated, and where SOX2 is active during blastocyst formation. Our data show that the roles and the regulation of SOX2 are unique compared to other pluripotency/reprogramming factors, such as OCT4 and NANOG. SOX2 marks pluripotent cells earlier than do other factors, but does not regulate pluripotency until several days later. Rather, the earlier role of SOX2 is to help establish the yolk sac lineage, which is essential for gestation.

Stat3 signaling regulates embryonic stem cell fate in a dose-dependent manner

Stat3 is essential for mouse embryonic stem cell (mESC) self-renewal mediated by LIF/gp130 receptor signaling. Current understanding of Stat3-mediated ESC self-renewal mechanisms is very limited, and has heretofore been dominated by the view that Stat3 signaling functions in a binary "on/off" manner. Here, in contrast to this binary viewpoint, we demonstrate a contextual, rheostat-like mechanism for Stat3's function in mESCs. Activation and expression levels determine whether Stat3 functions in a self-renewal or a differentiation role in mESCs. We also show that Stat3 induces rapid differentiation of mESCs toward the trophectoderm (TE) lineage when its activation level exceeds certain thresholds. Stat3 induces this differentiation phenotype via induction of Tfap2c and its downstream target Cdx2. Our findings provide a novel concept in the realm of Stat3, self-renewal signaling, and pluripotent stem cell biology. Ultimately, this finding may facilitate the development of conditions for the establishment of authentic non-rodent ESCs.

Transcriptional regulators of the trophoblast lineage in mammals with hemochorial placentation

Mammalian reproduction is critically dependent on the trophoblast cell lineage, which assures proper establishment of maternal-fetal interactions during pregnancy. Specification of trophoblast cell lineage begins with the development of the trophectoderm (TE) in preimplantation embryos. Subsequently, other trophoblast cell types arise with the progression of pregnancy. Studies with transgenic animal models as well as trophoblast stem/progenitor cells have implicated distinct transcriptional and epigenetic regulators in trophoblast lineage development. This review focuses on our current understanding of transcriptional and epigenetic mechanisms regulating specification, determination, maintenance and differentiation of trophoblast cells.

Histone variant H2A.X deposition pattern serves as a functional epigenetic mark for distinguishing the developmental potentials of iPSCs

For future application of induced pluripotent stem cell (iPSC) technology, the ability to assess the overall quality of iPSC clones will be an important issue. Here we show that the histone variant H2A.X is a functional marker that can distinguish the developmental potentials of mouse iPSC lines. We found that H2A.X is specifically targeted to and negatively regulates extraembryonic lineage gene expression in embryonic stem cells (ESCs) and prevents trophectoderm lineage differentiation. ESC-specific H2A.X deposition patterns are faithfully recapitulated in iPSCs that support the development of "all-iPS" animals via tetraploid complementation, the most stringent test available of iPSC quality. In contrast, iPSCs that fail to support all-iPS embryonic development show aberrant H2A.X deposition, upregulation of extraembryonic lineage genes, and a predisposition to extraembryonic differentiation. Thus, our work has highlighted an epigenetic mechanism for maintaining cell lineage commitment in ESCs and iPSCs that can be used to distinguish the quality of iPSC lines.

Sox2, a key factor in the regulation of pluripotency and neural differentiation

Sex determining region Y-box 2 (Sox2), a member of the SoxB1 transcription factor family, is an important transcriptional regulator in pluripotent stem cells (PSCs). Together with octamer-binding transcription factor 4 and Nanog, they co-operatively control gene expression in PSCs and maintain their pluripotency. Furthermore, Sox2 plays an essential role in somatic cell reprogramming, reversing the epigenetic configuration of differentiated cells back to a pluripotent embryonic state. In addition to its role in regulation of pluripotency, Sox2 is also a critical factor for directing the differentiation of PSCs to neural progenitors and for maintaining the properties of neural progenitor stem cells. Here, we review recent findings concerning the involvement of Sox2 in pluripotency, somatic cell reprogramming and neural differentiation as well as the molecular mechanisms underlying these roles.

Downregulation of miR-638 promotes invasion and proliferation by regulating SOX2 and induces EMT in NSCLC

Aberrant expression of microRNAs has been shown to regulate the biological processes of lung cancer cells. However, the role of miR-638 in the development of NSCLC is still unclear. In this study, low miR-638 and high SOX2 were shown to be associated with tumor size and metastasis of NSCLC patients. Downregulated miR-638 could promote cell invasion and proliferation, while high miR-638 expression reversed the effect. Furthermore, miR-638 could regulate SOX2 by directly binding to its 3'-UTR. Silencing of SOX2 by siRNA partially abolished the enhancement of cell invasion and proliferation induced by downregulated miR-638. Aberrant miR-638 expression could modulate the expression levels of markers of epithelial-to-mesenchymal transition. Our results indicate that miR-638 may play a pivotal role in the development of NSCLC.

Mechanisms for enhancing cellular reprogramming

During development, the genome adopts specific chromatin states to establish and maintain functionally distinct cell types in a well-controlled environment. A select group of transcription factors have the ability to drive the transition of the genome from a pluripotent to a more specialized chromatin state. The same set of factors can be used as reprogramming factors to reset the already established chromatin state back to pluripotency or directly to an alternative cell type. However, under the suboptimal reprogramming conditions, these factors fall short in guiding the majority of cells to their new fate. In this review, we visit the recent findings addressing the manipulation of chromatin structure to enhance the performance of transcription factors in reprogramming. The main emphasis is on the mechanisms underlying the conversion of somatic cells to pluripotency using OSKM. This review is intended to highlight the windows of opportunities for developing mechanistically based approaches to replace the phenotypically guided methods currently employed in reprogramming, in an attempt to move the field of cell conversion towards using next generation technologies.

miR-625 down-regulation promotes proliferation and invasion in esophageal cancer by targeting Sox2

miR-625 has been reported to exhibit abnormal expression in esophageal cancer (EC), but the mechanism and functions of miR-625 in esophageal cancer remain unclear. miR-625 down-regulation and Sox2 up-regulation were validated by qRT-PCR in 158 EC samples. Low expression of miR-625 promotes cell proliferation and invasion, while high expression of miR-625 has the opposite effect. Sox2, a target gene of miR-625, was examined by luciferase assay and western blot. Our data suggest that miR-625 may regulate the biological processes of EC via controlling Sox2 expression.