We compared two genetically highly defined transgenic systems to identify parameters affecting reprogramming of somatic cells to a pluripotent state. Our results demonstrate that the level and ...stoichiometry of reprogramming factors during the reprogramming process strongly influence the resulting pluripotency of iPS cells. High expression of Oct4 and Klf4 combined with lower expression of c-Myc and Sox2 produced iPS cells that efficiently generated “all-iPSC mice” by tetraploid (4n) complementation, maintained normal imprinting at the
Dlk1-
Dio3 locus, and did not create mice with tumors. Loss of imprinting (LOI) at the
Dlk1-Dio3 locus did not strictly correlate with reduced pluripotency though the efficiency of generating “all-iPSC mice” was diminished. Our data indicate that stoichiometry of reprogramming factors can influence epigenetic and biological properties of iPS cells. This concept complicates efforts to define a “generic” epigenetic state of iPSCs and ESCs and should be considered when comparing different iPS and ES cell lines.
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► Optimal reprogramming factor stoichiometry yields high-quality iPSCs ► Infrequent loss of imprinting (LOI) of Dlk1-Dio3 iPSCs seen in Col1a-OSKM mice ► Adult mice from Col1a1-OSKM iPSCs do not develop tumors ► Dlk1-Dio3 LOI is not an absolute marker for reduced pluripotency
Genome editing using the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated 9 (Cas9) technology is revolutionizing the study of gene function and likely will give ...rise to an entire new class of therapeutics for a wide range of diseases. Achieving this goal requires not only characterization of the technology for efficacy and specificity but also optimization of its delivery to the target cells for each disease indication. In this review we survey the various methods by which the CRISPR-Cas9 components have been delivered to cells and highlight some of the more clinically relevant approaches. Additionally, we discuss the methods available for assessing the specificity of Cas9 editing; an important safety consideration for development of the technology.
Developmental programs are controlled by transcription factors and chromatin regulators, which maintain specific gene expression programs through epigenetic modification of the genome. These ...regulatory events at enhancers contribute to the specific gene expression programs that determine cell state and the potential for differentiation into new cell types. Although enhancer elements are known to be associated with certain histone modifications and transcription factors, the relationship of these modifications to gene expression and developmental state has not been clearly defined. Here we interrogate the epigenetic landscape of enhancer elements in embryonic stem cells and several adult tissues in the mouse. We find that histone H3K27ac distinguishes active enhancers from inactive/poised enhancer elements containing H3K4me1 alone. This indicates that the amount of actively used enhancers is lower than previously anticipated. Furthermore, poised enhancer networks provide clues to unrealized developmental programs. Finally, we show that enhancers are reset during nuclear reprogramming.
Pluripotency can be induced in differentiated murine and human cells by retroviral transduction of Oct4, Sox2, Klf4, and c-Myc. We have devised a reprogramming strategy in which these four ...transcription factors are expressed from doxycycline (dox)-inducible lentiviral vectors. Using these inducible constructs, we derived induced pluripotent stem (iPS) cells from mouse embryonic fibroblasts (MEFs) and found that transgene silencing is a prerequisite for normal cell differentiation. We have analyzed the timing of known pluripotency marker activation during mouse iPS cell derivation and observed that alkaline phosphatase (AP) was activated first, followed by stage-specific embryonic antigen 1 (SSEA1). Expression of Nanog and the endogenous Oct4 gene, marking fully reprogrammed cells, was only observed late in the process. Importantly, the virally transduced cDNAs needed to be expressed for at least 12 days in order to generate iPS cells. Our results are a step toward understanding some of the molecular events governing epigenetic reprogramming.
T-cell acute lymphoblastic leukaemia (T-ALL) is a haematological malignancy with a dismal overall prognosis, including a relapse rate of up to 25%, mainly because of the lack of non-cytotoxic ...targeted therapy options. Drugs that target the function of key epigenetic factors have been approved in the context of haematopoietic disorders, and mutations that affect chromatin modulators in a variety of leukaemias have recently been identified; however, 'epigenetic' drugs are not currently used for T-ALL treatment. Recently, we described that the polycomb repressive complex 2 (PRC2) has a tumour-suppressor role in T-ALL. Here we delineated the role of the histone 3 lysine 27 (H3K27) demethylases JMJD3 and UTX in T-ALL. We show that JMJD3 is essential for the initiation and maintenance of T-ALL, as it controls important oncogenic gene targets by modulating H3K27 methylation. By contrast, we found that UTX functions as a tumour suppressor and is frequently genetically inactivated in T-ALL. Moreover, we demonstrated that the small molecule inhibitor GSKJ4 (ref. 5) affects T-ALL growth, by targeting JMJD3 activity. These findings show that two proteins with a similar enzymatic function can have opposing roles in the context of the same disease, paving the way for treating haematopoietic malignancies with a new category of epigenetic inhibitors.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The presence of two active X chromosomes (XaXa) is a hallmark of the ground state of pluripotency specific to murine embryonic stem cells (ESCs). Human ESCs (hESCs) invariably exhibit signs of X ...chromosome inactivation (XCI) and are considered developmentally more advanced than their murine counterparts. We describe the establishment of XaXa hESCs derived under physiological oxygen concentrations. Using these cell lines, we demonstrate that (1) differentiation of hESCs induces random XCI in a manner similar to murine ESCs, (2) chronic exposure to atmospheric oxygen is sufficient to induce irreversible XCI with minor changes of the transcriptome, (3) the Xa exhibits heavy methylation of the
XIST promoter region, and (4) XCI is associated with demethylation and transcriptional activation of
XIST along with H3K27-me3 deposition across the Xi. These findings indicate that the human blastocyst contains pre-X-inactivation cells and that this state is preserved in vitro through culture under physiological oxygen.
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► Conventional human ESCs (hESCs) have undergone X chromosome inactivation (XiXa) ► hESCs with two active X chromosomes (XaXa) can be isolated in 5% oxygen ► Oxidative and cellular stress induces irreversible epigenetic changes in hESCs ► Human blastocysts likely contain cells with two active X chromosomes (XaXa)
Embryogenesis requires the timely and coordinated activation of developmental regulators. It has been suggested that the recently discovered class of histone demethylases (UTX and JMJD3) that ...specifically target the repressive H3K27me3 modification play an important role in the activation of “bivalent” genes in response to specific developmental cues. To determine the requirements for UTX in pluripotency and development, we have generated Utx -null ES cells and mutant mice. The loss of UTX had a profound effect during embryogenesis. Utx -null embryos had reduced somite counts, neural tube closure defects and heart malformation that presented between E9.5 and E13.5. Unexpectedly, homozygous mutant female embryos were more severely affected than hemizygous mutant male embryos. In fact, we observed the survival of a subset of UTX-deficient males that were smaller in size and had reduced lifespan. Interestingly, these animals were fertile with normal spermatogenesis. Consistent with a midgestation lethality, UTX-null male and female ES cells gave rise to all three germ layers in teratoma assays, though sex-specific differences could be observed in the activation of developmental regulators in embryoid body assays. Lastly, ChIP-seq analysis revealed an increase in H3K27me3 in Utx -null male ES cells. In summary, our data demonstrate sex-specific requirements for this X-linked gene while suggesting a role for UTY during development.
Sertoli cells are considered the “supporting cells” of the testis that play an essential role in sex determination during embryogenesis and in spermatogenesis during adulthood. Their essential roles ...in male fertility along with their immunosuppressive and neurotrophic properties make them an attractive cell type for therapeutic applications. Here we demonstrate the generation of induced embryonic Sertoli-like cells (ieSCs) by ectopic expression of five transcription factors. We characterize the role of specific transcription factor combinations in the transition from fibroblasts to ieSCs and identify key steps in the process. Initially, transduced fibroblasts underwent a mesenchymal to epithelial transition and then acquired the ability to aggregate, formed tubular-like structures, and expressed embryonic Sertoli-specific markers. These Sertoli-like cells facilitated neuronal differentiation and self-renewal of neural progenitor cells (NPCs), supported the survival of germ cells in culture, and cooperated with endogenous embryonic Sertoli and primordial germ cells in the generation of testicular cords in the fetal gonad.
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► Nr5a1, Wt1, and Dmrt1 induce proliferation and mesenchymal to epithelial transition ► Nr5a1, Wt1, and Sox9 promote cell aggregation in various cell types ► Nr5a1, Wt1, Dmrt1, Gata4, Sox9 convert fibroblasts to embryonic Sertoli-like cells ► Induced cells contribute to fetal cord formation and to germ cell and NPC survival
Transcription-factor-mediated conversion of fibroblasts yields Sertoli-like cells with appropriate functional properties in vitro and after transplantation. Sertoli cells have a variety of potential applications for the treatment of fertility and neurological disorders.
The Pou domain containing transcription factor Oct4 is a well-established regulator of pluripotency in the inner cell mass of the mammalian blastocyst as well as in embryonic stem cells. While it has ...been shown that the Oct4 gene is inactivated through a series of epigenetic modifications following implantation, recent studies have detected Oct4 activity in a variety of somatic stem cells and tumor cells. Based on these observations it has been suggested that Oct4 may also function in maintaining self-renewal of somatic stem cells and, in addition, may promote tumor formation. We employed a genetic approach to determine whether Oct4 is important for maintaining pluripotency in the stem cell compartments of several somatic tissues including the intestinal epithelium, bone marrow (hematopoietic and mesenchymal lineages), hair follicle, brain, and liver. Oct4 gene ablation in these tissues revealed no abnormalities in homeostasis or regenerative capacity. We conclude that Oct4 is dispensable for both self-renewal and maintenance of somatic stem cells in the adult mammal.
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