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Epigenetic Modifications (epigenetic + modifications)
Selected AbstractsEpigenetic regulation of the imprinted U2af1-rs1 gene during retinoic acid-induced differentiation of embryonic stem cellsDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 6 2006Noelia Andollo Epigenetic modifications such as DNA methylation and changes in chromatin structure are changes in the chemical composition or structure of DNA that work by regulating gene expression. Their mechanisms of action have been generally studied in imprinted genes. The present work analyzes the involvement of these mechanisms in the expression of the U2af1-rs1 imprinted gene during the differentiation process of embryonic stem (ES) cells induced by retinoic acid. By DNA digestion with methylation-dependent or independent restriction enzymes and consecutive Southern blot, we have found that methylation of the U2af1-rs1 gene increases in differentiated ES cells and in embryoid bodies. However, northern blot and real-time reverse transcription,polymerase chain reaction analysis showed a higher expression of the U2af1-rs1 gene in differentiated ES cells and in embryoid bodies than in undifferentiated ones. On the other hand, the sensitivity to DNase-I assay demonstrated an open chromatin conformation for differentiated cells with regard to undifferentiated ES cells. Our results suggest that the expression of the U2af1-rs1 gene would be regulated by changes in chromatin structure rather than by DNA methylation during the RA-induced process of differentiation of ES cells. [source] Epigenetic modifications of SOX2 enhancers, SRR1 and SRR2, correlate with in vitro neural differentiation,JOURNAL OF NEUROSCIENCE RESEARCH, Issue 8 2008Marianna Sikorska Abstract SOX2 is a key neurodevelopmental gene involved in maintaining the pluripotency of stem cells and proliferation of neural progenitors and astroglia. Two evolutionally conserved enhancers, SRR1 and SRR2, are involved in controlling SOX2 expression during neurodevelopment; however, the molecular mechanisms regulating their activity are not known. We have examined DNA methylation and histone H3 acetylation at both enhancers in NT2-D1 progenitors, neurons and astrocytes, to establish the role of epigenetic mechanisms in cell-type-specific SOX2 expression. This study showed that 1) unmethylated DNA and acetylated histones at both enhancers correlated with a high level of SOX2 expression in proliferating neural progenitors and 2) reversible modifications of the SRR1 element were observed during gene reexpression in astrocytes, whereas permanent epigenetic marks on the SRR2 enhancer were seen in neurons where the gene was silenced. Taken together, these results are clear illustrations of cell-type-specific epigenomes and suggest mechanisms by which they may be created and maintained. © 2008 Wiley-Liss, Inc. [source] 5-azacitidine restores and amplifies the bicalutamide response on preclinical models of androgen receptor expressing or deficient prostate tumorsTHE PROSTATE, Issue 11 2010Giovanni Luca Gravina Abstract BACKGROUND Epigenetic modifications play a key role in the in prostate cancer (Pca) progression to a hormone refractory state (HRPC) and the current use of agents targeting epigenetic changes has become a topic of intense interest in cancer research. In this regard, 5-Azacitine (5-Aza) represents a promising epigenetic modulator. This study tested the hypothesis that 5-Aza may restore and enhance the responsiveness of HRPC cells to anti-hormonal therapy on Androgen receptor (AR) expressing (22rv1) and AR-deficient (PC3) cells. METHODS The effects were studied in vitro and in vivo models. This sequential treatment induced in vitro cell cycle arrest and apoptosis both in 22rv1 and PC3 tumor cell lines. RESULTS This combined treatment up-regulated the expression of FasL, phospho-FADD, p16INKA, Bax, Bak, and p21WAF1, and inhibited FLIP, Bcl-2, and Bcl-XL expression. The re-activation of hormonal response of AR-negative PC3 cell line was partially due to the AR re-expression mediated by 5-Aza treatment. In contrast, the increase in the response to anti-androgenic therapy in 22rv1 did not correlate with AR expression levels. Furthermore, xenograft studies revealed that the combined treatment of 5-Aza with AR-antagonist Bicalutamide had additive/synergistic effects in repressing tumor growth in vivo and the underlying mechanisms responsible for these effects seem to be in part mediated by induction of apoptosis. CONCLUSIONS So, this study strongly suggests a therapeutic potential of 5-Aza in combination with anti-androgen therapy in patients with in AR expressing and AR-deficient HRPC. Prostate 70: 1166,1178, 2010. © 2010 Wiley-Liss, Inc. [source] Setting and resetting of epigenetic marks in malignant transformation and developmentBIOESSAYS, Issue 8 2010Holger Richly Abstract Epigenetic modifications, such as DNA methylation and post-translation modifications of histones, have been shown to play an important role in chromatin structure, promoter activity, and cellular reprogramming. Large protein complexes, such as Polycomb and trithorax, often harbor multiple activities which affect histone tail modification. Nevertheless, the mechanisms underlying the deposition of these marks, their propagation during cell replication, and the alteration on their distribution during transformation still require further study. Here we review recent data on those processes in both normal and cancer cells, and we propose that the unscheduled expression of oncogenic transcription factors causes reprogramming of normal cells into cancer stem cells. [source] A challenge for regenerative medicine: Proper genetic programming, not cellular mimicryDEVELOPMENTAL DYNAMICS, Issue 12 2007Angie Rizzino Abstract Recent progress in stem cell biology and the reprogramming of somatic cells to a pluripotent phenotype has generated a new wave of excitement in regenerative medicine. Nonetheless, efforts aimed at understanding transdifferentiation, dedifferentiation, and the plasticity of cells, as well as the ability of somatic cells to be reprogrammed, has raised as many questions as those that have been answered. This review proffers the argument that many reports of transdifferentiation, dedifferentiation, and unexpected stem cell plasticity may be due to aberrant processes that lead to cellular look-alikes (cellular mimicry). In most cases, cellular look-alikes can now be identified readily by monitoring gene expression profiles, as well as epigenetic modifications of DNA and histone proteins of the cells involved. This review further argues that progress in regenerative medicine will be significantly hampered by failing to address the issue of cellular look-alikes. Developmental Dynamics 236:3199,3207, 2007. © 2007 Wiley-Liss, Inc. [source] Hormones as epigenetic signals in developmental programmingEXPERIMENTAL PHYSIOLOGY, Issue 6 2009Abigail L. Fowden In mammals, including man, epidemiological and experimental studies have shown that a range of environmental factors acting during critical periods of early development can alter adult phenotype. Hormones have an important role in these epigenetic modifications and can signal the type, severity and duration of the environmental cue to the developing feto-placental tissues. They affect development of these tissues both directly and indirectly by changes in placental phenotype. They act to alter gene expression, hence the protein abundance in a wide range of different tissues, which has functional consequences for many physiological systems both before and after birth. By producing an epigenome specific to the prevailing condition in utero, hormones act as epigenetic signals in developmental programming, with important implications for adult health and disease. This review examines the role of hormones as epigenetic signals by considering their responses to environmental cues, their effects on phenotypical development and the molecular mechanisms by which they programme feto-placental development, with particular emphasis on the glucocorticoids. [source] DNA methylation of Sleeping Beauty with transposition into the mouse genomeGENES TO CELLS, Issue 8 2005Chang Won Park The Sleeping Beauty transposon is a recently developed non-viral vector that can mediate insertion of transgenes into the mammalian genome. Foreign DNA elements that are introduced tend to invoke a host-defense mechanism resulting in epigenetic changes, such as DNA methylation, which may induce transcriptional inactivation of mammalian genes. To assess potential epigenetic modifications associated with Sleeping Beauty transposition, we investigated the DNA methylation pattern of transgenes inserted into the mouse genome as well as genomic regions flanking the insertion sites with bisulfite-mediated genomic sequencing. Transgenic mouse lines were created with two different Sleeping Beauty transposons carrying either the Agouti or eGFP transgene. Our results showed that DNA methylation in the keratin-14 promoter and Agouti transgene were negligible. In addition, two different genomic loci flanking the Agouti insertion site exhibited patterns of DNA methylation similar to wild-type mice. In contrast, high levels of DNA methylation were observed in the eGFP transgene and its ROSA26 promoter. These results indicate that transposition via Sleeping Beauty into the mouse genome may result in a significant level of de novo DNA methylation. This may depend on a number of different factors including the cargo DNA sequence, chromosomal context of the insertion site, and/or host genetic background. [source] Genetic redundancy in human cervical carcinoma cells: Identification of cells with "normal" propertiesINTERNATIONAL JOURNAL OF CANCER, Issue 10 2007Anastasia Bachmann Abstract Although it is generally assumed that cancer arises from a singular cell, a tumor must be considered as a dynamic and emergent biological structure, whose organizing principle is determined by genetic and epigenetic modifications, occurring variably in response to microenvironmental selection conditions. As previously shown, HPV-positive cervical carcinoma cells have lost their ability to induce IFN-, upon TNF-, treatment. However, regarding cancer as a non-linear system, which may, even in the absence of an apparent selection pressure, fluctuate between different "metastable" phenotypes, we demonstrate that TNF-, mediated IFN-, induction is not irreversibly disturbed in all cells. Using the IFN-, sensitive Encephalomyocarditis virus (EMCV) as a tool to monitor antiviral activity in long-term established malignant HeLa cells, rare IFN-, expressing clones were rescued from a population of non-responsive and EMCV-sensitive cells. Antiviral activity was mediated by the re-expression of IRF-1 and p48 (IRF-9), both key regulatory molecules normally found to be suppressed in cervical carcinoma cells. Upon inoculating of selected clones into immunocompromised animals, a reduced or even an absence of tumorigenicity of initially highly malignant cells could be discerned. These data indicate that both the absence of interferon signaling and the ability to form tumors were reversed in a minority of cells. We provide a paradigm for the existence of innate genetic redundancy mechanisms, where a particular phenotype persists and can be isolated without application of drugs generally changing the epigenetic context. © 2007 Wiley-Liss, Inc. [source] Programming the genome in embryonic and somatic stem cellsJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2007Philippe Collas ,,Introduction ,,Epigenetic makeup of embryonic stem cells: keeping chromatin loose -,DNA methylation and gene expression -,CpG methylation profiles in mouse ESCs -,CpG methylation patterns in human ESCs -,Both active and inactive histone modification marks on developmentally regulated genes in ESCs suggest transcriptional activation potential -,A regulatory role of histone H1 in gene expression in embryonic stem cells? -,Polycomb group proteins impose a transcriptional brake on lineage-priming genes ,,The epigenetic makeup of mesenchymal stem cells reflects restricted differentiation potential -,CpG methylation patterns on lineage-specific promoters in adipose stem cells -,CpG content affects the relationship between promoter DNA methylation and transcriptional activity -,Bivalent histone modifications on potentially active genes? ,,Linking DNA methylation to histone modifications, chromatin packaging and (re)organization of the nuclear compartment ,,Perspectives: towards remodelling the stem cell epigenome? Abstract In opposition to terminally differentiated cells, stem cells can self-renew and give rise to multiple cell types. Embryonic stem cells retain the ability of the inner cell mass of blastocysts to differentiate into all cell types of the body and have acquired in culture unlimited self-renewal capacity. Somatic stem cells are found in many adult tissues, have an extensive but finite lifespan and can differentiate into a more restricted array of cell types. A growing body of evidence indicates that multi-lineage differentiation ability of stem cells can be defined by the potential for expression of lineage-specification genes. Gene expression, or as emphasized here, potential for gene expression, is largely controlled by epigenetic modifications of DNA and chromatin on genomic regulatory and coding regions. These modifications modulate chromatin organization not only on specific genes but also at the level of the whole nucleus; they can also affect timing of DNA replication. This review highlights how mechanisms by which genes are poised for transcription in undifferentiated stem cells are being uncovered through primarily the mapping of DNA methylation, histone modifications and transcription factor binding throughout the genome. The combinatorial association of epigenetic marks on developmentally regulated and lineage-specifying genes in undifferentiated cells seems to define a pluripotent state. [source] X-linked mental retardation and epigeneticsJOURNAL OF CELLULAR AND MOLECULAR MEDICINE, Issue 4 2006Guy Froyen Abstract The search for the genetic defects in constitutional diseases has so far been restricted to direct methods for the identification of genetic mutations in the patients' genome. Traditional methods such as karyotyping, FISH, mutation screening, positional cloning and CGH, have been complemented with newer methods including array-CGH and PCR-based approaches (MLPA, qPCR). These methods have revealed a high number of genetic or genomic aberrations that result in an altered expression or reduced functional activity of key proteins. For a significant percentage of patients with congenital disease however, the underlying cause has not been resolved strongly suggesting that yet other mechanisms could play important roles in their etiology. Alterations of the ,native' epigenetic imprint might constitute such a novel mechanism. Epigenetics, heritable changes that do not rely on the nucleotide sequence, has already been shown to play a determining role in embryonic development, X-inactivation, and cell differentiation in mammals. Recent progress in the development of techniques to study these processes on full genome scale has stimulated researchers to investigate the role of epigenetic modifications in cancer as well as in constitutional diseases. We will focus on mental impairment because of the growing evidence for the contribution of epigenetics in memory formation and cognition. Disturbance of the epigenetic profile due to direct alterations at genomic regions, or failure of the epigenetic machinery due to genetic mutations in one of its components, has been demonstrated in cognitive derangements in a number of neurological disorders now. It is therefore tempting to speculate that the cognitive deficit in a significant percentage of patients with unexplained mental retardation results from epigenetic modifications. [source] DNA methylation pattern changes upon long-term culture and aging of human mesenchymal stromal cellsAGING CELL, Issue 1 2010Simone Bork Summary Within 2,3 months of in vitro culture-expansion, mesenchymal stromal cells (MSC) undergo replicative senescence characterized by cell enlargement, loss of differentiation potential and ultimate growth arrest. In this study, we have analyzed DNA methylation changes upon long-term culture of MSC by using the HumanMethylation27 BeadChip microarray assessing 27 578 unique CpG sites. Furthermore, we have compared MSC from young and elderly donors. Overall, methylation patterns were maintained throughout both long-term culture and aging but highly significant differences were observed at specific CpG sites. Many of these differences were observed in homeobox genes and genes involved in cell differentiation. Methylation changes were verified by pyrosequencing after bisulfite conversion and compared to gene expression data. Notably, methylation changes in MSC were overlapping in long-term culture and aging in vivo. This supports the notion that replicative senescence and aging represent developmental processes that are regulated by specific epigenetic modifications. [source] The emerging role of epigenetic modifications and chromatin remodeling in spinal muscular atrophyJOURNAL OF NEUROCHEMISTRY, Issue 6 2009Sebastian Lunke Abstract As the leading genetic cause for infantile death, Spinal Muscular Atrophy (SMA) has been extensively studied since its first description in the early 1890s. Though today much is known about the cause of the disease, a cure or effective treatment is not currently available. Recently the short chain fatty acid valproic acid, a drug used for decades in the management of epilepsy and migraine therapy, has been shown to elevate the levels of the essential survival motor neuron protein in cultured cells. In SMA mice, valproic acid diminished the severity of the disease phenotype. This effect was linked to the ability of the short chain fatty acid to suppress histone deacetylase activity and activate gene transcription. Since then, the study of different histone deacetylase inhibitors and their epigenetic modifying capabilities has been of high interest in an attempt to find potential candidates for effective treatment of SMA. In this review, we summarize the current knowledge about use of histone deacetylase inhibitors in SMA as well as their proposed effects on chromatin structure and discuss further implications for possible treatments of SMA arising from research examining epigenetic change. [source] Emerging Role of Epigenetics in the Actions of AlcoholALCOHOLISM, Issue 9 2008Shivendra D. Shukla This review deals with the recent developments on the epigenetic effects of ethanol. A large body of data have come from studies in liver and in neuronal systems and involve post-translational modifications in histones and methylations in DNA. Ethanol causes site selective acetylation, methylation, and phosphorylation in histone. With respect to methylations the methyl group donating system involving S-adenosyl methionine appears to play a central role. There is contrasting effect of acetylation versus methylation on the same site of histone, as it relates to the transcriptional activation. Epigenetic memory also appears to correlate with liver pathology and Mallory body formation. Experimental evidence supports transcriptional regulation of genes in the CNS by DNA methylations. These studies are contributing towards a better understanding of a novel epigenetic regulation of gene expression in the context of alcohol. The critical steps and the enzymes (e.g., histone acetyltransferase, histone deacetylase, DNA methyltransferase) responsible for the epigenetic modifications are prime targets for intense investigation. The emerging data are also beginning to offer novel insight towards defining the molecular actions of ethanol and may contribute to potential therapeutic targets at the nucleosomal level. These epigenetic studies have opened up a new avenue of investigation in the alcohol field. [source] Characterization of the methylation patterns of MS4A2 in atopic cases and controlsALLERGY, Issue 3 2010M. A. R. Ferreira To cite this article: Ferreira MAR, Oates NA, van Vliet J, Zhao ZZ, Ehrich M, Martin NG, Montgomery GW, Whitelaw E, Duffy DL. Characterization of the methylation patterns of MS4A2 in atopic cases and controls. Allergy 2010; 65: 333,337. Abstract Background:, It is largely unknown whether epigenetic modifications of key genes may contribute to the reported maternal effects in atopy. The aim of this study was to characterize the methylation patterns of the membrane-spanning 4-domains, subfamily A, member 2 gene (MS4A2) (,-chain of the IgE high-affinity receptor), a key gene in the allergic cascade. Methods:, Mass spectrometry and bisulphite sequencing were used to measure the methylation of two potential substrates for epigenetic regulation of MS4A2, namely a predicted promoter and a CpG-rich AluSp repeat. Methylation was measured in DNA extracted from peripheral blood lymphocytes of 38 atopic cases and 37 controls. Cases were positive for atopy, asthma, bronchial hyper-responsiveness and had high IgE levels. Both parents of eight atopic cases were also tested. Results:, The AluSp element was highly methylated across all individuals (mean 0.92, range 0.87,0.94), a pattern inconsistent with classical imprinting. Variation in methylation at this locus was not associated with age, sex, daily steroid use or atopic status, and there were no differences in methylation between mothers and fathers of atopic cases. Bisulphite sequencing analysis of the promoter region showed that it was also not imprinted, and there was no evidence for allele-specific methylation, but we were unable to test for association with atopy status. Conclusions:, Methylation levels at the AluSp repeat analysed in MS4A2 were inconsistent with classical imprinting mechanisms and did not associate with atopy status. The promoter region was less methylated but further analysis of this region in larger cohorts is warranted to investigate its role in allergic disease. [source] Microbial exposure, interferon gamma gene demethylation in naïve T-cells, and the risk of allergic diseaseALLERGY, Issue 3 2009P. J. Vuillermin The period of immune programming during early life presents a critical window of opportunity for the prevention of allergic diseases. There is mounting evidence that inappropriate immune programming may involve disruption of specific epigenetic modifications (switches) at immune-related genes. This novel area of research has great potential, as epigenetic changes are known to be sensitive to environmental factors and may therefore provide a mechanistic link for the observed association between specific environmental cues, faulty immune development, and the risk of allergic disease. In addition, the dynamic and potentially reversible nature of epigenetic modifications offers potentially novel targets for therapeutic and/or preventative interventions. We review the evidence that (1) failure to up-regulate the interferon gamma (IFN,) response during infancy is an important determinant of the risk of allergic disease, (2) expression of the IFN, gene in naïve T-cells is regulated by epigenetic mechanisms, and (3) failure to up-regulate IFN, gene expression of naïve T-cells associated with low early life microbial exposure. Taken together, these lines of evidence suggest that low microbial exposure during early life increases the risk of allergic disease by reducing demethylation (activation) of the IFN, gene of naive T-cells. [source] Molecular engineering of resveratrol in plantsPLANT BIOTECHNOLOGY JOURNAL, Issue 1 2009Bertrand Delaunois Summary The grapevine phytoalexin resveratrol, the synthesis of which is achieved by stilbene synthase (STS), displays a wide range of biological effects. Most interest has centred, in recent years, on STS gene transfer experiments from grapevine to the genome of numerous plants. This work presents a comprehensive review on plant molecular engineering with the STS gene. Gene and promoter options are discussed, namely the different promoters used to drive the transgene, as well as the enhancer elements and/or heterologous promoters used to improve transcriptional activity in the transformed lines. Factors modifying transgene expression and epigenetic modifications, for instance transgene copy number, are also presented. Resveratrol synthesis in plants, together with that of its glucoside as a result of STS expression, is described, as is the incidence of these compounds on plant metabolism and development. The ectopic production of resveratrol can lead to broad-spectrum resistance against fungi in transgenic lines, and to the enhancement of the antioxidant activities of several fruits, highlighting the potential role of this compound in health promotion and plant disease control. [source] In Vitro Compaction of Germinal Vesicle Chromatin is Beneficial to Survival of Vitrified Cat OocytesREPRODUCTION IN DOMESTIC ANIMALS, Issue 2009P Comizzoli Contents The immature cat oocyte contains a large-sized germinal vesicle (GV) with decondensed chromatin that is highly susceptible to cryo-damage. The aim of the study was to explore an alternative to conventional cryopreservation by examining the influence of GV chromatin compaction using resveratrol (Res) exposure (a histone deacetylase enhancer) on oocyte survival during vitrification. In Experiment 1, denuded oocytes were exposed to 0, 0.5, 1.0 or 1.5 mmol/l Res for 1.5 h and then evaluated for chromatin structure or cultured to assess oocyte meiotic and developmental competence in vitro. Exposure to 1.0 or 1.5 mmol/l Res induced complete GV chromatin deacetylation and the most significant compaction. Compared to other treatments, the 1.5 mmol/l Res concentration compromised the oocyte ability to achieve metaphase II (MII) or to form a blastocyst. In Experiment 2, denuded oocytes were exposed to Res as in Experiment 1 and cultured in vitro either directly (fresh) or after vitrification. Both oocyte types then were assessed for meiotic competence, fertilizability and ability to form embryos. Vitrification exerted an overall negative influence on oocyte meiotic and developmental competence. However, ability to reach MII, achieve early first cleavage, and develop to an advanced embryo stage (8,16 cells) was improved in vitrified oocytes previously exposed to 1.0 mmol/l Res compared to all counterpart treatments. In summary, results reveal that transient epigenetic modifications associated with GV chromatin compaction induced by Res is fully reversible and beneficial to oocyte survival during vitrification. This approach has allowed the production of the first cat embryos from vitrified immature oocytes. [source] The role of DNA methylation, nucleosome occupancy and histone modifications in paramutationTHE PLANT JOURNAL, Issue 3 2010Max Haring Summary Paramutation is the transfer of epigenetic information between alleles that leads to a heritable change in expression of one of these alleles. Paramutation at the tissue-specifically expressed maize (Zea mays) b1 locus involves the low-expressing B, and high-expressing B-I allele. Combined in the same nucleus, B, heritably changes B-I into B,. A hepta-repeat located 100-kb upstream of the b1 coding region is required for paramutation and for high b1 expression. The role of epigenetic modifications in paramutation is currently not well understood. In this study, we show that the B, hepta-repeat is DNA-hypermethylated in all tissues analyzed. Importantly, combining B, and B-I in one nucleus results in de novo methylation of the B-I repeats early in plant development. These findings indicate a role for hepta-repeat DNA methylation in the establishment and maintenance of the silenced B, state. In contrast, nucleosome occupancy, H3 acetylation, and H3K9 and H3K27 methylation are mainly involved in tissue-specific regulation of the hepta-repeat. Nucleosome depletion and H3 acetylation are tissue-specifically regulated at the B-I hepta-repeat and associated with enhancement of b1 expression. H3K9 and H3K27 methylation are tissue-specifically localized at the B, hepta-repeat and reinforce the silenced B, chromatin state. The B, coding region is H3K27 dimethylated in all tissues analyzed, indicating a role in the maintenance of the silenced B, state. Taken together, these findings provide insight into the mechanisms underlying paramutation and tissue-specific regulation of b1 at the level of chromatin structure. [source] Epigenetic changes in cancer,APMIS, Issue 10 2007KIRSTEN GRØNBÆK A cancer develops when a cell acquires specific growth advantages through the stepwise accumulation of heritable changes in gene function. Basically, this process is directed by changes in two different classes of genes: Tumor suppressor genes that inhibit cell growth and survival and oncogenes that promote cell growth and survival. Since several alterations are usually required for a cancer to fully develop, the malignant phenotype is determined by the compound status of tumor suppressor genes and oncogenes. Cancer genes may be changed by several mechanisms, which potentially alter the protein encoding nucleotide template, change the copy number of genes, or lead to increased gene transcription. Epigenetic alterations, which, by definition, comprise mitotically and meiotically heritable changes in gene expression that are not caused by changes in the primary DNA sequence, are increasingly being recognized for their roles in carcinogenesis. These epigenetic alterations may involve covalent modifications of amino acid residues in the histones around which the DNA is wrapped, and changes in the methylation status of cytosine bases (C) in the context of CpG dinucleotides within the DNA itself. Methylation of clusters of CpGs called "CpG-islands" in the promoters of genes has been associated with heritable gene silencing. The present review will focus on how disruption of the epigenome can contribute to cancer. In contrast to genetic alterations, gene silencing by epigenetic modifications is potentially reversible. Treatment by agents that inhibit cytosine methylation and histone deacetylation can initiate chromatin decondensation, demethylation and reestablishment of gene transcription. Accordingly, in the clinical setting, DNA methylation and histone modifications are very attractive targets for the development and implementation of new therapeutic approaches. Many clinical trials are ongoing, and epigenetic therapy has recently been approved by the United States Food and Drug Administration (US FDA) for use in the treatment of myelodysplastic syndrome (MDS) and primary cutaneous T-cell lymphoma (CTCL). [source] Imprinting and looping: epigenetic marks control interactions between regulatory elementsBIOESSAYS, Issue 1 2005Yuzuru Kato Gene regulation involves various cis -regulatory elements that can act at a distance. They may physically interact each other or with their target genes to exert their effects. Such interactions are beginning to be uncovered in the imprinted Igf2/H19 domain.1 The differentially methylated regions (DMRs), containing insulators, silencers and activators, were shown to have physical contacts between them. The interactions were changeable depending on their epigenetic state, presumably enabling Igf2 to move between an active and a silent chromatin domain. The study gives us a novel view on how regulatory elements influence gene expression and how epigenetic modifications modulate their long-range effects. BioEssays 27:1,4, 2005. © 2004 Wiley Periodicals, Inc. [source] | |||||||||||||||||||||||||