The POU transcription factor Oct-3/4 has been shown to be critical for maintaining embryonic stem (ES) cell character. However, the molecular mechanisms underlying its function remain elusive. We have previously shown that among the POU transcription factor family of proteins, Oct-3/4 alone is able to bind to the regulatory region of the UTF1 gene bearing a variant octamer sequence together with Sox-2. Here, we demonstrate using Oct-3/4-Oct-6 chimeras that there is a precise correlation between the ability of proteins to form a complex on the UTF1 enhancer with Sox-2 and the ability to maintain the stem cell state in ES cells. Different chimeric proteins show differential abilities to form a Sox-2-containing complex on the UTF1 regulatory region, with a decrease in efficiency of the complex formation accompanied by a decrease in the level of UTF1 expression and the rate of cell proliferation. Overexpression of UTF1 in these slow-growing cells was able to restore their proliferation rate to wild-type levels. Moreover, UTF1 was also observed to have an effect on teratoma formation. These results suggest a molecular pathway by which Oct-3/4 induces rapid proliferation and tumorigenic properties of ES cells through activation of the UTF1 gene.

BACKGROUND & AIMS Fibrosis is an abnormal extension of the wound healing process that follows tissue damage; it is involved in pathogenesis in a variety of chronic diseases. The formation of extracellular matrix is an essential response in wound healing. Although it has been proposed that collagen organization and assembly depend on the fibronectin matrix in culture, the contribution of fibronectin to these processes remains to be defined in vivo. METHODS We generated a conditional, fibronectin-deficient mouse model of liver injury and explored whether fibronectin would be a suitable target for preventing extensive collagen deposits and scar formation that could lead to liver fibrosis. RESULTS The lack of fibronectin did not interfere with reconstruction of collagen fibril organization in response to liver injury. Signaling by transforming growth factor (TGF)-β and type V collagen were required for collagen fibrillogenesis during remodeling of adult liver tissue. CONCLUSIONS TGF-β and type V collagen are targets for regulating the initial fibrogenic response to liver damage.

Many genes have been identified that are specifically expressed in multiple types of stem cells in their undifferentiated state. It is generally assumed that at least some of these putative "stemness" genes are involved in maintaining properties that are common to all stem cells. We compared gene expression profiles between undifferentiated and differentiated embryonic stem cells (ESCs) using DNA microarrays. We identified several genes with much greater signal in undifferentiated ESCs than in their differentiated derivatives, among them the putative stemness gene encoding junctional adhesion molecule B (Jam-B gene). However, in spite of the specific expression in undifferentiated ESCs, Jam-B mutant ESCs had normal morphology and pluripotency. Furthermore, Jam-B homozygous mutant mice are fertile and have no overt developmental defects. Moreover, we found that neural and hematopoietic stem cells recovered from Jam-B mutant mice are not impaired in their ability to self-renew and differentiate. These results demonstrate that Jam-B is dispensable for normal mouse development and stem cell identity in embryonic, neural, and hematopoietic stem cells.Embryonic stem cells (ESCs) are derived from mammalian preimplantation embryos and possess the remarkable ability to differentiate into all embryonic cell types. Moreover, they can grow indefinitely without losing this pluripotency if cultured under appropriate conditions. A number of key transcription factors, such as OCT-4, Nanog, and FOXD3 (5,7,12,22,25), have been shown to be essential for sustaining ESC properties. However, it is not known how these molecules contribute to maintenance of the pluripotent state.Somatic stem cells, including neural stem cells (NSCs) and hematopoietic stem cells (HSCs), share some of the properties of ESCs, including multipotency and self-renewal. In the event of severe injury, numerous types of tissue-specific stem cells can give rise to cells of heterologous lineages (39,42,43), although in some cases, fusion of stem cells with other cells appears to be involved in transdifferentiation (21, 29, 46). Thus, it is possible that ESCs and somatic stem cells share a common genetic program that maintains stem cell identity (20,37,40,42). Recently, Ivanova et al. (13) identified 283 genes or expressed sequence tags, including a gene encoding junctional adhesion molecule B (JAM-B) (nomenclature of the protein in NCBI Database is JAM2), that are expressed in three different stem cell lines, by means of DNA microarray analysis. Although it is assumed that at least some of these genes are involved in the maintenance of stem cell properties, no data confirming this have yet been reported.Here we investigate this possibility. We have focused on Jam-B, a putative "stemness" gene identified by Ivanova et al. (13), because of the extreme difference in expression levels between undifferentiated and differentiated ESCs. Jam-B encodes an immunoglobulin superfamily protein that is specific to tight junctions and mediates cell-cell contacts between T cel...

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The interphase nucleus is a highly ordered and compartmentalized organelle, yet it maintains dynamic flexibility with regard to both structure and function. Little is known regarding what elaborate mechanisms might exist to explain these properties of the nucleus. Also unresolved is whether some architectural components might facilitate the formation of functional intranuclear compartments or higher order chromatin structure. As the first step to address these questions, we performed an in-depth proteome analysis of nuclear insoluble fractions of human HeLa-S3 cells prepared by two different approaches: a high-salt/detergent/nuclease-resistant fraction and a lithium 3,5-diiodosalicylate/nuclease-resistant fraction. Proteins of the fractions were analyzed by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS), identifying 333 and 330 proteins from each fraction, respectively. Among the insoluble nuclear proteins, we identified 50 hitherto unknown or functionally uncharacterized proteins. The subcellular distribution of selected proteins, including DEK oncogene protein, and SON protein, demonstrated their novel associations with nuclear insoluble materials, corroborating our MS-based analysis. This study establishes a comprehensive catalog of the nuclear insoluble proteins in human cells. Further functional analysis of the proteins identified in our study will significantly improve our understanding of the dynamic organization of the interphase nucleus.

In female mammals, the dosage difference in X-linked genes between XX females and XY males is compensated for by inactivating one of the two X chromosomes during early development. Since the discovery of the X inactive-specific transcript (XIST) gene in humans and its subsequent isolation of the mouse homolog, Xist, in the early 1990s, the molecular basis of X chromosome inactivation (X-inactivation) has been more fully elucidated using genetically manipulated mouse embryos and embryonic stem cells. Studies on X-inactivation in other mammals, although limited when compared with those in the mice, have revealed that, while their inactive X chromosome shares many features with those in the mice, there are marked differences in not only some epigenetic modifications of the inactive X chromosome but also when and how X-inactivation is initiated during early embryonic development. Such differences raise the issue about what extent of the molecular basis of X-inactivation in the mice is commonly shared among others. Recognizing similarities and differences in X-inactivation among mammals may provide further insight into our understanding of not only the evolutionary but also the molecular aspects for the mechanism of X-inactivation. Here, we reviewed species-specific differences in X-inactivation and discussed what these differences may reveal.

The Src family kinases (SFKs) are believed to play critical roles in malignant transformation, as well as in growth, invasion and dissemination of neoplastic tissue. Inhibition of SFK-mediated signal transduction and activation of downstream targets inhibits tumor progression. To determine whether constitutive activity of SFK per se is sufficient to induce tumorigenesis in vivo, we have generated a mouse model with a keratinocyte-restricted deletion of the SFK-negative regulator csk (Csk-K5 mice). Even though expression levels of SFKs were lower in C-terminal Src kinase (Csk)-null keratinocytes, activity levels were higher than in control keratinocytes. At the age of 3 months, all Csk-K5 mice displayed signs of chronic inflammation in dermis and epidermal hyperplasia. About 19% of Csk-K5 mice (7 out of 36) developed papillomatous lesions. However, these lesions did not show any signs of neoplastic transformation over the next 8 months. Epidermal hyperplasia and hyperkeratosis in Csk-K5 mice were associated with an increased number of stem cells in the interfollicular epidermis, an increased proliferation of basal keratinocytes and a delayed terminal differentiation of the suprabasal keratinocytes. Our results clearly demonstrate that even though SFK-mediated signaling promotes tumor progression, elevated activity of SFKs in vivo alone is not sufficient to induce neoplastic transformation.

Stable silencing of the inactive X chromosome (Xi) in female mammals is critical for the development of embryos and their postnatal health. SmcHD1 is essential for stable silencing of the Xi, and its functional deficiency results in derepression of many X-inactivated genes. Although SmcHD1 has been suggested to play an important role in the formation of higher order chromatin structure of the Xi, the underlying mechanism is largely obscure. Here we explore the epigenetic state of the Xi in SmcHD1-deficient epiblast stem cells (EpiSCs) and mouse embryonic fibroblasts (MEFs) in comparison with their wild-type counterparts. The results suggest that SmcHD1 underlies the formation of H3K9me3-enriched blocks on the Xi, which, although the importance of H3K9me3 has been largely overlooked in mice, play a critical role in the establishment of the stably silenced state. We propose that the H3K9me3 blocks formed on the Xi facilitate robust heterochromatin formation in combination with H3K27me3, and the substantial loss of H3K9me3 caused by SmcHD1 deficiency leads to aberrant distribution of H3K27me3 on the Xi and derepression of X-inactivated genes.