Search

Direct conversion from fibroblasts to generate hepatocyte like-cells (iHeps) bypassing the pluripotent state has been described in previous reports as an attractive method acquiring hepatocytes for cell-based therapy. The limited proliferation of iHeps, however, has hampered it uses in cell-based therapy. Since hepatic stem cells (HepSCs) possess self-renewal and bipotency with the capacity to differentiate into both hepatocytes and cholangiocytes, they have therapeutic potential for treating liver disease. Here, we investigated the therapeutic effects of induced HepSCs (iHepSCs) on a carbon tetrachloride (CCl4)-induced liver fibrosis model. We demonstrate that Oct4 and Hnf4a are sufficient to convert fibroblasts into expandable iHepSCs. Hepatocyte-like cells derived from iHepSCs (iHepSC-HEPs) exhibit the typical morphology of hepatocytes and hepatic functions, including glycogen storage, low-density lipoprotein (LDL) uptake, Indocyanine green (ICG) detoxification, drug metabolism, urea production, and albumin secretion. iHepSCs-derived cholangiocyte-like cells (iHepSC-CLCs) expressed cholangiocyte-specific markers and formed cysts and tubule-like structures with apical-basal polarity and secretory function in three-dimensional culture condition. Furthermore, iHepSCs showed anti-inflammatory and anti-fibrotic effects in CCl4-induced liver fibrosis. This study demonstrates that Oct4 and Hnf4α-induced HepSCs show typical hepatic and biliary functionality in vitro. It also presents the therapeutic effect of iHepSCs in liver fibrosis. Therefore, directly converting iHepSCs from somatic cells may facilitate the development of patient-specific cell-based therapy for chronic liver damage. [ABSTRACT FROM AUTHOR]

Expression of germ cell nuclear factor (GCNF; Nr6a1), an orphan member of the nuclear receptor gene family of transcription factors, during gastrulation and neurulation is critical for normal embryogenesis in mice. Gcnf represses the expression of the POU-domain transcription factor Oct4 (Pou5f1) during mouse post-implantation development. Although Gcnf expression is not critical for the embryonic segregation of the germ cell lineage, we found that sexually dimorphic expression of Gcnf in germ cells correlates with the expression of pluripotency-associated genes, such as Oct4, Sox2, and Nanog, as well as the early meiotic marker gene Stra8. To elucidate the role of Gcnf during mouse germ cell differentiation, we generated an ex vivo Gcnf-knockdown model in combination with a regulated CreLox mutation of Gcnf. Lack of Gcnf impairs normal spermatogenesis and oogenesis in vivo, as well as the derivation of germ cells from embryonic stem cells (ESCs) in vitro. Inactivation of the Gcnf gene in vivo leads to loss of repression of Oct4 expression in both male and female gonads. [ABSTRACT FROM AUTHOR]

Many of the structural and mechanistic requirements of oocyte-mediated nuclear reprogramming remain elusive. Previous accounts that transcriptional reprogramming of somatic nuclei in mouse zygotes may be complete in 24–36 hours, far more rapidly than in other reprogramming systems, raise the question of whether the mere exposure to the activated mouse ooplasm is sufficient to enact reprogramming in a nucleus. We therefore prevented DNA replication and cytokinesis, which ensue after nuclear transfer, in order to assess their requirement for transcriptional reprogramming of the key pluripotency genes Oct4 (Pou5f1) and Nanog in cloned mouse embryos. Using transcriptome and allele-specific analysis, we observed that hundreds of mRNAs, but not Oct4 and Nanog, became elevated in nucleus-transplanted oocytes without DNA replication. Progression through the first round of DNA replication was essential but not sufficient for transcriptional reprogramming of Oct4 and Nanog, whereas cytokinesis and thereby cell-cell interactions were dispensable for transcriptional reprogramming. Responses similar to clones also were observed in embryos produced by fertilization in vitro. Our results link the occurrence of reprogramming to a previously unappreciated requirement of oocyte-mediated nuclear reprogramming, namely DNA replication. Nuclear transfer alone affords no immediate transition from a somatic to a pluripotent gene expression pattern unless DNA replication is also in place. This study is therefore a resource to appreciate that the quest for always faster reprogramming methods may collide with a limit that is dictated by the cell cycle. [ABSTRACT FROM AUTHOR]

Maintenance and maturation of primordial germ cells is controlled by complex genetic and epigenetic cascades, and disturbances in this network lead to either infertility or malignant aberration. Transcription factor TFAP2C has been described to be essential for primordial germ cell maintenance and to be upregulated in several human germ cell cancers. Using global gene expression profiling, we identified genes deregulated upon loss of Tfap2c in embryonic stem cells and primordial germ cell-like cells. We show that loss of Tfap2c affects many aspects of the genetic network regulating germ cell biology, such as downregulation of maturation markers and induction of markers indicative for somatic differentiation, cell cycle, epigenetic remodeling and pluripotency. Chromatin-immunoprecipitation analyses demonstrated binding of TFAP2C to regulatory regions of deregulated genes (Sfrp1, Dmrt1, Nanos3, c-Kit, Cdk6, Cdkn1a, Fgf4, Klf4, Dnmt3b and Dnmt3l) suggesting that these genes are direct transcriptional targets of TFAP2C in primordial germ cells. Since Tfap2c deficient primordial germ cell-like cells display cancer related deregulations in epigenetic remodeling, cell cycle and pluripotency control, the Tfap2c-knockout allele was bred onto 129S2/Sv genetic background. There, mice heterozygous for Tfap2c develop with high incidence germ cell cancer resembling human pediatric germ cell tumors. Precursor lesions can be observed as early as E16.5 in developing testes displaying persisting expression of pluripotency markers. We further demonstrate that mice with a heterozygous deletion of the TFAP2C target gene Nanos3 are also prone to develop teratomas. These data highlight TFAP2C as a critical and dose-sensitive regulator of germ cell fate. [ABSTRACT FROM AUTHOR]

To know the map between transcription factors (TFs) and their binding sites is essential to reverse engineer the regulation process. Only about 10%-20% of the transcription factor binding motifs (TFBMs) have been reported. This lack of data hinders understanding gene regulation. To address this drawback, we propose a computational method that exploits never used TF properties to discover the missing TFBMs and their sites in all human gene promoters. The method starts by predicting a dictionary of regulatory "DNA words." From this dictionary, it distills 4098 novel predictions. To disclose the crosstalk between motifs, an additional algorithm extracts TF combinatorial binding patterns creating a collection of TF regulatory syntactic rules. Using these rules, we narrowed down a list of 504 novel motifs that appear frequently in syntax patterns. We tested the predictions against 509 known motifs confirming that our system can reliably predict ab initio motifs with an accuracy of 81%--far higher than previous approaches. We found that on average, 90% of the discovered combinatorial binding patterns target at least 10 genes, suggesting that to control in an independent manner smaller gene sets, supplementary regulatory mechanisms are required. Additionally, we discovered that the new TFBMs and their combinatorial patterns convey biological meaning, targeting TFs and genes related to developmental functions. Thus, among all the possible available targets in the genome, the TFs tend to regulate other TFs and genes involved in developmental functions. We provide a comprehensive resource for regulation analysis that includes a dictionary of "DNA words," newly predicted motifs and their corresponding combinatorial patterns. Combinatorial patterns are a useful filter to discover TFBMs that play a major role in orchestrating other factors and thus, are likely to lock/unlock cellular functional clusters. [ABSTRACT FROM AUTHOR]

Transcription factor-based reprogramming can lead to the successful switching of cell fates. We have recently reported that mouse embryonic fibroblasts (MEFs) can be directly reprogrammed into induced neural stem cells (iNSCs) after the forced expression of Brn4, Sox2, Klf4, and Myc. Here, we tested whether iNSCs could be further reprogrammed into induced pluripotent stem cells (iPSCs). The two factors Oct4 and Klf4 were sufficient to induce pluripotency in iNSCs. Immunocytochemistry and gene expression analysis showed that iNSC-derived iPSCs (iNdiPSCs) are similar to embryonic stem cells at the molecular level. In addition, iNdiPSCs could differentiate into cells of all three germ layers, both in vitro and in vivo, proving that iNdiPSCs are bona fide pluripotent cells. Furthermore, analysis of the global gene expression profile showed that iNdiPSCs, in contrast to iNSCs, do not retain any MEF transcriptional memory even at early passages after reprogramming. Overall, our results demonstrate that iNSCs can be reprogrammed to pluripotency and suggest that cell fate can be redirected numerous times. Importantly, our findings indicate that the induced pluripotent cell state may erase the donor-cell type epigenetic memory more efficiently than other induced somatic cell fates. [ABSTRACT FROM AUTHOR]

Epiblast stem cells (EpiSCs) and embryonic stem cells (ESCs) differ in their in vivo differentiation potential. While ESCs form teratomas and efficiently contribute to the development of chimeras, EpiSCs form teratomas but very rarely chimeras. In contrast to their differentiation potential, the reprogramming potential of EpiSCs has not yet been investigated. Here we demonstrate that the epiblast-derived pluripotent stem cells EpiSCs and P19 embryonal carcinoma cells (ECCs) exhibit a lower reprogramming potential than ESCs and F9 ECCs. In addition, we show that the low reprogramming ability is due to the lower levels of Sox2 in epiblast-derived stem cells. Consistent with this observation, overexpression of Sox2 enhances reprogramming efficiency. In summary, these findings suggest that a low reprogramming potential is a general feature of epiblast-derived stem cells and that the Sox2 level is a determinant of the cellular reprogramming potential. [ABSTRACT FROM AUTHOR]

Neurosphere cell culture is a commonly used model to study the properties and potential applications of neural stem cells (NSCs). However, standard protocols to culture NSCs have yet to be established, and the mechanisms underlying NSC survival and maintenance of their undifferentiated state, in response to the growth factors FGF-2 and EGF are not fully understood. Using cultures of embryonic and adult olfactory bulb stem cells (eOBSCs and aOBSCs), we analyzed the consequences of FGF-2 and EGF addition at different intervals on proliferation, cell cycle progression, cell death and differentiation, as well as on global gene expression. As opposed to cultures supplemented daily, addition of FGF-2 and EGF every 4 days significantly reduced the neurosphere volume and the total number of cells in the spheres, mainly due to increased cell death. Moreover, partial FGF-2 and EGF deprivation produced an increase in OBSC differentiation during the proliferative phase. These changes were more evident in aOBSC than eOBSC cultures. Remarkably, these effects were accompanied by a significant upregulation in the expression of endogenous Fgf-2 and genes involved in cell death and survival (Cryab), lipid catabolic processes (Pla2g7), cell adhesion (Dscaml1), cell differentiation (Dscaml1, Gpr17, S100b, Ndrg2) and signal transduction (Gpr17, Ndrg2). These findings support that a daily supply of FGF-2 and EGF is critical to maintain the viability and the undifferentiated state of NSCs in culture, and they reveal novel molecular hallmarks of NSC death, survival and the initiation of differentiation.