Genomic Imprinting in Development and Disease

发育和疾病中的基因组印记

• 批准号: 6763664
• 负责人: COLIN STEWART
• 金额: --
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 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/6763664
• 关键词: cell growth regulation; cell proliferation; cyclin dependent kinase; developmental genetics; embryogenesis; enzyme inhibitors; gene expression; gene induction /repression; gene targeting; genetic disorder; genetically modified animals; genomic imprinting; growth factor receptors; insulinlike growth factor; laboratory mouse; mammalian embryology; tissue /cell culture

Unlike the majority of genes expressed in mammals, imprinted genes are expressed from only one parental allele- which allele depends on the particular gene. Thus the Insulin like growth factor 2 (Igf2) is expressed almost exclusively from the paternal allele, whereas p57Kip2, a CDK inhibitor is expressed from the maternal allele. This form of gene regulation is, among vertebrates, unique to mammals. Why it exists is still unclear. Much evidence has suggested that imprinted genes are involved in regulating cell proliferation and viability. Androgenetic embryos, in which the entire genome is paternal in origin, exhibit overgrowth of the extraembryonic membranes and in increase in fetal size at mid gestation. Parthenogenetic embryos, where the entire genome is maternal in origin show retarded embryonic growth. To facilitate an understanding of imprinting and to identify novel imprinted genes, we established fibroblast lines which are either exclusively androgenetic or parthenogenetic in origin. The lines show diametrically opposite patterns of growth with the androgenetic cells having a shorter cell cycle time, reaching a higher saturation density and forming tumors, whereas the parthenotes senesced and died. Using mouse lines deficient for imprinted genes such as Igf2, one of its receptors, the Igf2r, and p57Kip2 revealed that Igf2 was a major determinant regulating proliferation and viability of these cells. In addition to these growth studies, we have used these lines to identify novel imprinted genes. Using a suppressive subtractive screen we identified the nuclear receptor cofactor repressor/activator Zac1 and epsilon sarcoglycan as being imprinted genes expressed from the paternal allele, as well as an Est that is strongly expressed in the brain, and is transcribed from the maternal allele. Current studies are centered on determining the function of these genes in development and growth regulation. We are developing mouse models for a human congenital disease associated with a defect in imprinting called Prader-Willi syndrome. In this condition, newborns are hypotonic, have breathing difficulties and often fail to thrive. Those that survive develop an eating disorder and frequently become obese. The disease is associated with loss of part of the paternal chromosome 15. A homologous region is found on mouse chromosome 7. We recently described the derivation of mice lacking the paternal allele of a gene Necdin located in the Prader-Willi region. Such mice die shortly after birth due to respiratory problems and have mimicked one aspect of Prader-Willi syndrome. Their respiratory physiology is being studied in greater detail to determine the function of Necdin. Overall, a molecular analysis of imprinting should provide insights into the epigenetic control of gene expression, an aspect that is of increasing relevance to understanding the inactivation of certain tumor suppressor genes in cancer formation.

与大多数在哺乳动物中表达的基因不同，印记基因仅从一个亲本等位基因表达-哪个等位基因取决于特定的基因。因此，胰岛素样生长因子2（Igf 2）几乎完全由父本等位基因表达，而p57 Kip 2（CDK抑制剂）由母本等位基因表达。在脊椎动物中，这种形式的基因调控是哺乳动物所独有的。它为什么存在还不清楚。许多证据表明，印记基因参与调节细胞增殖和活力。雄激素胚胎，其中整个基因组是父系起源，表现出过度生长的胚外膜和增加胎儿的大小在中期妊娠。单性生殖胚胎，其中整个基因组都是母系起源，表现出胚胎生长迟缓。为了便于理解印迹和识别新的印迹基因，我们建立了成纤维细胞系，这是完全雄激素或孤雌生殖的起源。这些细胞系显示出完全相反的生长模式，雄激素细胞具有较短的细胞周期时间，达到较高的饱和密度并形成肿瘤，而单性生殖细胞衰老并死亡。使用缺乏印迹基因如Igf 2、其受体之一Igf 2 r和p57 Kip 2的小鼠品系，发现Igf 2是调节这些细胞增殖和活力的主要决定因素。 除了这些生长研究之外，我们还使用这些品系来鉴定新的印迹基因。使用抑制性消减筛选，我们确定了核受体辅因子阻遏物/激活剂Zac 1和β-肌聚糖作为从父亲等位基因表达的印记基因，以及在大脑中强烈表达的Est，并从母亲等位基因转录。目前的研究集中在确定这些基因在发育和生长调节中的功能。 我们正在开发一种与印记缺陷有关的人类先天性疾病的小鼠模型，称为普拉德-威利综合征。在这种情况下，新生儿是低渗，有呼吸困难，往往无法茁壮成长。那些幸存下来的人会患上饮食失调症，并经常变得肥胖。这种疾病与父亲15号染色体的部分丢失有关。在小鼠7号染色体上发现一个同源区域。我们最近描述了小鼠的起源缺乏位于Prader-Willi区域的基因Necdin的父系等位基因。这些小鼠在出生后不久就死于呼吸系统疾病，并模仿了普拉德-威利综合征的一个方面。他们的呼吸生理学正在进行更详细的研究，以确定Necdin的功能。 总体而言，印迹的分子分析应提供见解的基因表达的表观遗传控制，一个方面是越来越多的相关性，以了解某些肿瘤抑制基因在癌症形成中的失活。