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Epigenetic mechanisms regulating the Igf2/H19 and Kcnq1 locus

调节 Igf2/H19 和 Kcnq1 位点的表观遗传机制

基本信息

批准号：
8736854
负责人：
Karl Eric Pfeifer
金额：
$ 141.41万
依托单位：
EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH & HUMAN DEVELOPMENT
依托单位国家：
美国
项目类别：
财政年份：
资助国家：
美国
起止时间：
至
项目状态：
未结题

来源：
https://reporter.nih.gov/project-details/8736854
关键词：
11p15.5 7-dehydrocholesterol reductase Address Adrenergic Agents Affect Age Alleles Animals Area Arrhythmia Beckwith-Wiedemann Syndrome Behavior Biological Models Biological Process Calcium ion Calsequestrin Cardiac Cardiac Myocytes Cell Differentiation process Cell Nucleus Cell physiology Cells Cholesterol Chromatin Structure Chromosomes Chromosomes, Human, Pair 7 Clinical Collaborations Coupling DNA Modification Process Defect Deletion Mutagenesis Development Developmental Process Disease Distal Drug usage Elements Epigenetic Process Fathers Fibroblasts Functional RNA Gene Cluster Gene Expression Gene Expression Profile Gene Expression Regulation Gene Mutation Genes Genetic Genetic Enhancer Element Genetic Transcription Genomics Germ Cells Goals Growth and Development function H19 gene Heart Human In Vitro Inherited Insertional Mutagenesis Intervention Ion Channel Late Effects Mammals Metabolism Methylation Modeling Molecular Mothers Mus Muscle Cells Mutation National Institute of Child Health and Human Development Nephroblastoma Parents Pathway interactions Patients Pattern Phenotype Pilot Projects Proteins Protocols documentation Regulation Research Role Sarcoplasmic Reticulum Smith-Lemli-Opitz Syndrome Structure Surface Testing Therapeutic Intervention Tissues Transcriptional Silencer Elements Work adrenergic base cancer type cell growth cell type cholesterol biosynthesis coping mechanism developmental disease disease phenotype efficacy testing enzyme activity epigenome gain of function gene function gene therapy genetic analysis human disease imprint induced pluripotent stem cell mouse model muscle regeneration mutant novel premature prevent programs promoter relating to nervous system research study restoration small molecule stem cell technology therapeutic target transcription factor transcriptome sequencing voltage

项目摘要

Imprinting represents a curious defiance of normal Mendelian genetics. Mammals inherit two complete sets of chromosomes, one from the mother and one from the father, and most autosomal genes will be expressed equally from maternal and paternal alleles. Imprinted genes, however, are expressed from only one chromosome in a parent-of-origin dependent manner. Because silent and active promoters are present in a single nucleus, the differences in activity cannot be explained by transcription factor abundance. Thus the transcription of imprinted genes represents a clear situation in which epigenetic mechanisms restrict gene expression. Therefore imprinted genes are good models for understanding the role of DNA modifications and chromatin structure in maintaining appropriate patterns of gene expression. Further, because of parent-of-origin restricted expression, phenotypes determined by imprinted genes are not only susceptible to mutations of the genes themselves but also to disruptions in the epigenetic programs controlling regulation. Thus imprinted genes are frequently associated with human diseases, including disorders affecting cell growth, development, and behavior. Our Section is investigating a cluster of genes on the distal end of mouse chromosome 7. The syntenic region in humans on chromosome 11p15.5 is conserved in genomic organization and in monoallelic expression patterns. Especially, we are focusing on the molecular basis for the maternal specific expression of the H19 gene and the paternal specific expression of the Igf2 gene. Loss of imprinting mutations in these two genes is associated with Beckwith Wiedemann Syndrome (BWS) and with Wilms tumor. Expression of both H19 and Igf2 is dependent upon a shared set of enhancer elements downstream of both genes. We have identified a 2.4 kb ICR (for Imprinting Control Region) upstream of the H19 promoter. Using conditional deletion and insertional mutagenesis we have identified three functions associated with this element. First, this element acts to distinguish the parental origin of any chromosome into which it is inserted. Specifically, the CpGs within this region become hypermethylated upon paternal inheritance. Second, this element functions as a CTCF-dependent, methylation-sensitive transcriptional insulator. By reorganizing the long-range interactions of nearby promoter and enhancer elements, this insulator is able to direct parental-specific activation of nearby genes. Finally, this ICR also acts as a developmentally regulated silencer element when paternally inherited. Specifically, the methylated ICR induces changes in chromatin structure of neighboring sequences that impacts gene expression. Our current goals are to identify and characterize the protein factors and non-coding RNAs that interact with the ICR and establish the chromatin structures associated with the maternal and paternal chromosomes. We are addressing these issues both in germ cells, where the imprints are established, and in somatic tissues where expression of Igf2 and H19 are most critical for normal, healthy cell function. Finally, we are also working to establish mouse models that mimic diseases phenotypes associated with loss of imprinting in humans. Most recently we have demonstrated defects in muscle cell differentiation and in muscle regeneration in cells where Igf2/H19 imprinting is disrupted. Through RNA-seq experiments we are characterizing the molecular pathways downstream of the imprinting defect that are responsible for the disease phenotye. A second research goal is to generate mouse models for cardiac arrhythmias. We first focused on uncovering the biological function of the imprinted Kcnq1 gene, located just upstream of Igf2. More recently, we have generated mouse models for Calsequestrin2 deficiency. We demonstrated that calsequestrin2 is not essential for cardiac calcium ion storage, which can be maintained by an expansion of the sarcoplasmic reticulum (SR) volume and surface area. Rather, the primary function of calsequestrin appears to be the regulation of the SR calcium ion release channel during conditions of beta-adrenergic stimulation. The loss of calsequestrin2 thus results in premature calcium ion release from the SR, leading to voltage changes that result in premature contraction of cardiomyocytes and thus arrhythmia. The validity of this mouse model has been recently confirmed by demonstration that drugs that we used to successfully ameliorate the mouse arrhythmias were highly effective in pilot studies on human patients. In the past year, we have demonstrated that the arrhythmias associated with calsequestrin2-deficiency worsen signficantly with age. We have recently generated and are now analyzing conditional alleles of calsequestrin 2. Using these models we have analyzed the effect of late-onset loss of calsequestrin 2 gene function, thus modeling a common human condition. Our results indicate that the phenotypes associated with loss of gene function late in development are much more severe. Thus we we believe that the the developing heart has mechanisms for coping aberrant regulation of Ca++ metabolism that can permanently protect the heart. We are initiating genomic approaches that will identify these mechanism and then evaluate whether these mechanisms represent therapeutic targets. We are also now determining the effect of restoration of calsequestrin 2 gene function to animals that have developed in the absence of any active calsequestrin 2 gene. Together these experiments will help us understand how calsequestin 2 gene activity regulates sarcoplasmic reticulum structure and also help us develop novel therapies for human patients with both congenital and acquired deficiencies in Ca++ excitation-contraction coupling. Finally, to make full use of our expertise in stem cell technologies, we recently began a collaboration with FD Porter, also at the NICHD, to establish and characterize iPSC cells established using fibroblasts isolated from patients carrying mutations in the gene encoding 7-dehydrocholesterol reductase (DHCR7). Mutations in DHCR7 are associated with Smith-Lemli-Opitz syndrome (SLOS). Disruption in DHCR7 enzyme activity prevents the final steps in cholesterol biosynthesis and therefore leads to decreased cholesterol levels as well as the accumulation of cholesterol precursors. In the presence of exogenous cholesterol, wild type and DHCR7-mutant iPSCs are not distinguishable in terms of their in vitro differentiation capabilities. However, in the absence of added cholesterol, mutant cells show high levels of spontaneous differentiation to neural progeny. Rescue of the differentiation defect occurs not only with adding cholesterol but with several small molecules. Current studies focus on identifying the relevant genetic pathways and on identifying small molecules that can rescue the phenotype fully and therefore might be candidates for SLOS therapies.

印记是对正常孟德尔遗传学的一种奇特的挑战。哺乳动物遗传了两套完整的染色体，一套来自母亲，一套来自父亲，大多数常染色体基因将从母亲和父亲的等位基因中平等地表达。然而，印迹基因仅在一条染色体上以依赖于亲本的方式表达。由于沉默启动子和活跃启动子存在于单个细胞核中，活性的差异不能用转录因子丰度来解释。因此，印迹基因的转录代表了表观遗传机制限制基因表达的明确情况。因此，印迹基因是理解DNA修饰和染色质结构在维持适当的基因表达模式中的作用的良好模型。此外，由于亲本的限制性表达，由印迹基因决定的表型不仅容易受到基因本身突变的影响，而且还容易受到控制调控的表观遗传程序的破坏。因此，印迹基因经常与人类疾病有关，包括影响细胞生长、发育和行为的疾病。