Author Correction: Contrasting roles of histone 3 lysine 27 demethylases in acute lymphoblastic leukaemia.
Explore the source record for details and available documents.
Published Erratum↗
Biomedical subjects
Rudolf Jaenisch
Publications and source records attributed to Rudolf Jaenisch.
Contrasting roles of histone 3 lysine 27 demethylases in acute lymphoblastic leukaemia.
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.
Animals↗
Molecular control of pluripotency.
Transcriptional regulators and epigenetic modifiers play crucial roles throughout development to ensure that proper gene expression patterns are established and maintained in any given cell type. Recent genome-wide studies have begun to unravel how genetic and epigenetic factors maintain the undifferentiated state of embryonic stem cells while allowing these cells to remain poised to differentiate into somatic cells in response to developmental cues. These studies provide a conceptual framework for understanding pluripotency and lineage-specification at the molecular level.
Animals↗
Nuclear reprogramming and pluripotency.
The cloning of mammals from differentiated donor cells has refuted the old dogma that development is an irreversible process. It has demonstrated that the oocyte can reprogramme an adult nucleus into an embryonic state that can direct development of a new organism. The prospect of deriving patient-specific embryonic stem cells by nuclear transfer underscores the potential use of this technology in regenerative medicine. The future challenge will be to study alternatives to nuclear transfer in order to recapitulate reprogramming in a Petri dish without the use of oocytes.
Animals↗
Reprogramming efficiency following somatic cell nuclear transfer is influenced by the differentiation and methylation state of the donor nucleus.
Reprogramming of a differentiated cell nucleus by somatic cell nuclear transplantation is an inefficient process. Following nuclear transfer, the donor nucleus often fails to express early embryonic genes and establish a normal embryonic pattern of chromatin modifications. These defects correlate with the low number of cloned embryos able to produce embryonic stem cells or develop into adult animals. Here, we show that the differentiation and methylation state of the donor cell influence the efficiency of genomic reprogramming. First, neural stem cells, when used as donors for nuclear transplantation, produce embryonic stem cells at a higher efficiency than blastocysts derived from terminally differentiated neuronal donor cells, demonstrating a correlation between the state of differentiation and cloning efficiency. Second, using a hypomorphic allele of DNA methyltransferase-1, we found that global hypomethylation of a differentiated cell genome improved cloning efficiency. Our results provide functional evidence that the differentiation and epigenetic state of the donor nucleus influences reprogramming efficiency.
Animals↗
NT-3 facilitates hippocampal plasticity and learning and memory by regulating neurogenesis.
In the adult brain, the expression of NT-3 is largely confined to the hippocampal dentate gyrus (DG), an area exhibiting significant neurogenesis. Using a conditional mutant line in which the NT-3 gene is deleted in the brain, we investigated the role of NT-3 in adult neurogenesis, hippocampal plasticity, and memory. Bromodeoxyuridine (BrdU)-labeling experiments demonstrated that differentiation, rather than proliferation, of the neuronal precursor cells (NPCs) was significantly impaired in DG lacking NT-3. Triple labeling for BrdU, the neuronal marker NeuN, and the glial marker GFAP indicated that NT-3 affects the number of newly differentiated neurons, but not glia, in DG. Field recordings revealed a selective impairment in long-term potentiation (LTP) in the lateral, but not medial perforant path-granule neuron synapses. In parallel, the NT-3 mutant mice exhibited deficits in spatial memory tasks. In addition to identifying a novel role for NT-3 in adult NPC differentiation in vivo, our study provides a potential link between neurogenesis, dentate LTP, and spatial memory.
Animals↗
A bivalent chromatin structure marks key developmental genes in embryonic stem cells.
The most highly conserved noncoding elements (HCNEs) in mammalian genomes cluster within regions enriched for genes encoding developmentally important transcription factors (TFs). This suggests that HCNE-rich regions may contain key regulatory controls involved in development. We explored this by examining histone methylation in mouse embryonic stem (ES) cells across 56 large HCNE-rich loci. We identified a specific modification pattern, termed "bivalent domains," consisting of large regions of H3 lysine 27 methylation harboring smaller regions of H3 lysine 4 methylation. Bivalent domains tend to coincide with TF genes expressed at low levels. We propose that bivalent domains silence developmental genes in ES cells while keeping them poised for activation. We also found striking correspondences between genome sequence and histone methylation in ES cells, which become notably weaker in differentiated cells. These results highlight the importance of DNA sequence in defining the initial epigenetic landscape and suggest a novel chromatin-based mechanism for maintaining pluripotency.
Animals↗
Control of developmental regulators by Polycomb in human embryonic stem cells.
Polycomb group proteins are essential for early development in metazoans, but their contributions to human development are not well understood. We have mapped the Polycomb Repressive Complex 2 (PRC2) subunit SUZ12 across the entire nonrepeat portion of the genome in human embryonic stem (ES) cells. We found that SUZ12 is distributed across large portions of over two hundred genes encoding key developmental regulators. These genes are occupied by nucleosomes trimethylated at histone H3K27, are transcriptionally repressed, and contain some of the most highly conserved noncoding elements in the genome. We found that PRC2 target genes are preferentially activated during ES cell differentiation and that the ES cell regulators OCT4, SOX2, and NANOG cooccupy a significant subset of these genes. These results indicate that PRC2 occupies a special set of developmental genes in ES cells that must be repressed to maintain pluripotency and that are poised for activation during ES cell differentiation.
Animals↗
Polycomb complexes repress developmental regulators in murine embryonic stem cells.
The mechanisms by which embryonic stem (ES) cells self-renew while maintaining the ability to differentiate into virtually all adult cell types are not well understood. Polycomb group (PcG) proteins are transcriptional repressors that help to maintain cellular identity during metazoan development by epigenetic modification of chromatin structure. PcG proteins have essential roles in early embryonic development and have been implicated in ES cell pluripotency, but few of their target genes are known in mammals. Here we show that PcG proteins directly repress a large cohort of developmental regulators in murine ES cells, the expression of which would otherwise promote differentiation. Using genome-wide location analysis in murine ES cells, we found that the Polycomb repressive complexes PRC1 and PRC2 co-occupied 512 genes, many of which encode transcription factors with important roles in development. All of the co-occupied genes contained modified nucleosomes (trimethylated Lys 27 on histone H3). Consistent with a causal role in gene silencing in ES cells, PcG target genes were de-repressed in cells deficient for the PRC2 component Eed, and were preferentially activated on induction of differentiation. Our results indicate that dynamic repression of developmental pathways by Polycomb complexes may be required for maintaining ES cell pluripotency and plasticity during embryonic development.
Animals↗
Politically correct human embryonic stem cells?
Explore the source record for details and available documents.
Animals↗
The disease progression of Mecp2 mutant mice is affected by the level of BDNF expression.
Mutations in the MECP2 gene cause Rett syndrome (RTT). Bdnf is a MeCP2 target gene; however, its role in RTT pathogenesis is unknown. We examined Bdnf conditional mutant mice for RTT-relevant pathologies and observed that loss of BDNF caused smaller brain size, smaller CA2 neurons, smaller glomerulus size, and a characteristic hindlimb-clasping phenotype. BDNF protein level was reduced in Mecp2 mutant mice, and deletion of Bdnf in Mecp2 mutants caused an earlier onset of RTT-like symptoms. To assess whether this interaction was functional and potentially therapeutically relevant, we increased BDNF expression in the Mecp2 mutant brain with a conditional Bdnf transgene. BDNF overexpression extended the lifespan, rescued a locomotor defect, and reversed an electrophysiological deficit observed in Mecp2 mutants. Our results provide in vivo evidence for a functional interaction between Mecp2 and Bdnf and demonstrate the physiological significance of altered BDNF expression/signaling in RTT disease progression.
Action Potentials↗
ES cells derived from cloned and fertilized blastocysts are transcriptionally and functionally indistinguishable.
Reproductive cloning is uniformly rejected as a valid technology in humans because of the severely abnormal phenotypes seen in cloned animals. Gene expression aberrations observed in tissues of cloned animals have also raised concerns regarding the therapeutic application of "customized" embryonic stem (ES) cells derived by nuclear transplantation (NT) from a patient's somatic cells. Although previous experiments in mice have demonstrated that the developmental potential of ES cells derived from cloned blastocysts (NT-ES cells) is identical to that of ES cells derived from fertilized blastocysts, a systematic molecular characterization of NT-ES cell lines is lacking. To investigate whether transcriptional aberrations, similar to those observed in tissues of cloned mice, also occur in NT-ES cells, we have compared transcriptional profiles of 10 mouse NT- and fertilization-derived-ES cell lines. We report here that the ES cell lines derived from cloned and fertilized mouse blastocysts are indistinguishable based on their transcriptional profiles, consistent with their normal developmental potential. Our results indicate that, in contrast to embryonic and fetal development of clones, the process of NT-ES cell derivation rigorously selects for those immortal cells that have erased the "epigenetic memory" of the donor nucleus and, thus, become functionally equivalent. Our findings support the notion that ES cell lines derived from cloned or fertilized blastocysts have an identical therapeutic potential.
Animals↗
Mammalian nuclear transfer.
During development, the genetic content of each cell remains, with a few exceptions, identical to that of the zygote. Differentiated cells, therefore, retain all the genetic information necessary to generate an entire organism (nuclear totipotency). Nuclear transfer (NT) was initially developed to test experimentally this concept by cloning animals from differentiated cells. It has, since then, been used to study the role of genetic and epigenetic alterations during development and disease. In this review, we highlight some of the milestones in mammalian NT reached in the 50 years after the first nuclear transplantations in frogs. We also address problems associated with mammalian nuclear transfer and provide a survey on current NT and stem cell technology. In the long term, nuclear transfer or alternative strategies aim to generate customized pluripotent cells, which would be invaluable to medical research and therapy.
Animals↗
Efficient method to generate single-copy transgenic mice by site-specific integration in embryonic stem cells.
Transgenic and gene-targeted mutant mice provide powerful tools for analysis of the cellular processes involved in early development and in the pathogenesis of many diseases. Here we describe a transgene integration strategy mediated by site-specific recombination that allows establishment of multiple embryonic stem (ES) cell lines carrying tetracycline-inducible genes targeted to a specific locus to assure predictable temporal and spatial expression in ES cells and mice. Using homologous recombination we inserted an frt homing site into which tetracycline-inducible transgenes can be integrated efficiently in the presence of FLPe recombinase. This strategy and the vectors described here are generally applicable to any locus in ES cells and should allow for the rapid production of mice with transgenes efficiently targeted to a defined site.
Alleles↗
Severe deficits in 5-HT2A -mediated neurotransmission in BDNF conditional mutant mice.
BDNF is thought to provide critical trophic support for serotonin neurons. In order to determine postnatal effects of BDNF on the serotonin system, we examined a line of conditional mutant mice that have normal brain content of BDNF during prenatal development but later depletion of this neurotrophin in the postnatal period. These mice show a behavioral phenotype that suggests serotonin dysregulation. However, as shown here, the presynaptic serotonin system in the adult conditional mutant mice appeared surprisingly normal from histological, biochemical, and electrophysiological perspectives. By contrast, a dramatic and unexpected postsynaptic 5-HT2A deficit in the mutant mice was found. Electrophysiologically, serotonin neurons appeared near normal except, most notably, for an almost complete absence of expected 5-HT2A -mediated glutamate and GABA postsynaptic potentials normally displayed by these neurons. Further analysis showed that BDNF mutants had much reduced 5-HT2A receptor protein in dorsal raphe nucleus and a similar deficit in prefrontal cortex, a region that normally shows a high level of 5-HT2A receptor expression. Recordings in prefrontal slice showed a marked deficit in 5-HT2A -mediated excitatory postsynaptic currents, similar to that seen in the dorsal raphe. These findings suggest that postnatal levels of BDNF play a relatively limited role in maintaining presynaptic aspects of the serotonin system and a much greater role in maintaining postsynaptic 5-HT2A and possibly other receptors than previously suspected.
Animals↗
Hematopoietic precursor cells transiently reestablish permissiveness for X inactivation.
Xist is the trigger for X inactivation in female mammals. The long noncoding Xist RNA localizes along one of the two female X chromosomes and initiates chromosome-wide silencing in the early embryo. In differentiated cells, Xist becomes dispensable for the maintenance of the inactive X, and its function for initiation of silencing is lost. How Xist mediates gene repression remains an open question. Here, we use an inducible Xist allele in adult mice to identify cells in which Xist can cause chromosome-wide silencing. We show that Xist has the ability to initiate silencing in immature hematopoietic precursor cells. In contrast, hematopoietic stem cells and mature blood cells are unable to initiate ectopic X inactivation. This indicates that pathways critical for silencing are transiently activated in hematopoietic differentiation. Xist-responsive cell types in normal female mice show a change of chromatin marks on the inactive X. However, dosage compensation is maintained throughout hematopoiesis. Therefore, Xist can initiate silencing in precursors with concomitant maintenance of dosage compensation. This suggests that Xist function is restricted in development by the limited activity of epigenetic pathways rather than by a change in the responsiveness of chromatin between embryonic and differentiated cell types.
Alleles↗
Suppression of intestinal neoplasia by deletion of Dnmt3b.
Aberrant gene silencing accompanied by DNA methylation is associated with neoplastic progression in many tumors that also show global loss of DNA methylation. Using conditional inactivation of de novo methyltransferase Dnmt3b in Apc(Min/+) mice, we demonstrate that the loss of Dnmt3b has no impact on microadenoma formation, which is considered the earliest stage of intestinal tumor formation. Nevertheless, we observed a significant decrease in the formation of macroscopic colonic adenomas. Interestingly, many large adenomas showed regions with Dnmt3b inactivation, indicating that Dnmt3b is required for initial outgrowth of macroscopic adenomas but is not required for their maintenance. These results support a role for Dnmt3b in the transition stage between microadenoma formation and macroscopic colonic tumor growth and further suggest that Dnmt3b, and by extension de novo methylation, is not required for maintaining tumor growth after this transition stage has occurred.
Adenoma↗
Generation of nuclear transfer-derived pluripotent ES cells from cloned Cdx2-deficient blastocysts.
The derivation of embryonic stem (ES) cells by nuclear transfer holds great promise for research and therapy but involves the destruction of cloned human blastocysts. Proof of principle experiments have shown that 'customized' ES cells derived by nuclear transfer (NT-ESCs) can be used to correct immunodeficiency in mice. Importantly, the feasibility of the approach has been demonstrated recently in humans, bringing the clinical application of NT-ESCs within reach. Altered nuclear transfer (ANT) has been proposed as a variation of nuclear transfer because it would create abnormal nuclear transfer blastocysts that are inherently unable to implant into the uterus but would be capable of generating customized ES cells. To assess the experimental validity of this concept we have used nuclear transfer to derive mouse blastocysts from donor fibroblasts that carried a short hairpin RNA construct targeting Cdx2. Cloned blastocysts were morphologically abnormal, lacked functional trophoblast and failed to implant into the uterus. However, they efficiently generated pluripotent embryonic stem cells when explanted into culture.
Animals↗