Phylogenetic Comparisons of Imprinted Domains

描述（由申请人提供）：基因组印记是指导致亲本来源依赖性单等位基因表达的基因的表观遗传标记。印记基因在胚胎生长和行为中起着关键作用;许多基因也作为体细胞中的癌症易感基因座，因为它们的功能性单倍体状态使它们容易失活或过度表达。在印记中心的区域控制下，印记基因的位置聚集加剧了这种高度的易感性，当印记中心在遗传或表观遗传上被破坏时，会导致包括癌症在内的多遗传表型异常。印记基因也可能在机械上将营养扰动（如甲基化缺陷）直接与癌症病因联系起来，因为它们的顺式作用调控元件在表观遗传学上是不稳定的。我们建议使用系统发育比较的orthopathic序列从现存的三个哺乳动物的命令，Prototheria，Metatheria和真兽目的成员的印记域结构的演变特征和定义的基本顺式作用的印记调控元件，表观遗传区分父母的等位基因，也构成目标表观遗传失调。这项拨款申请的总体假设是，基因启动子沉默代表了原始的印记机制，而持续的双亲间遗传冲突导致了一些印记域的监管复杂性增加，因为母亲和父亲的基因组进化出了抵消策略来克服基因抑制。因此，印记机制被假定为在更古老的哺乳动物中不那么复杂。为了验证这一新的假设，我们最近制作了细菌人工染色体（BAC）文库，从印记负鼠（Didelphus virginiana）和非印记鸭嘴兽（Ornithorhynchus anatinus）检查印记域包含基因参与癌症，由三种不同的印记机制。表达的母体抑制将通过NNAT（神经元素）建模;反义转录物表达的父本抑制将通过M6 P/IGF 2 R建模，并且通过IGF 2/H19和DLK 1/MEG 3印迹结构域建模通过间插印迹中心对并置基因的相互亲本抑制。我们将测试在这些比较中确定的新的调控元件的功能相关性，确定它们是否可以直接收购的转基因小鼠的印记。这些比较系统发育研究的成功完成将大大提高我们对这种独特的哺乳动物形式的基因调控的进化的理解。这些研究也将是关键的识别新的印记基因，并表征已知的不太明确的印记域窝藏遗传和/或表观遗传突变，机械参与癌症和神经遗传性疾病，如精神分裂症，双相情感障碍和自闭症。

DESCRIPTION (provided by applicant): Genomic imprinting refers to an epigenetic marking of genes that results in parent-of-origin dependent, monoallelic expression. Imprinted genes have critical roles in embryonic growth and behavior; many also function as cancer susceptibility loci in somatic cells because their functionally haploid state makes them vulnerable to inactivation or overexpression. This heightened susceptibility is exacerbated by positional clustering of imprinted genes under the regional control of imprinting centers that, when disrupted genetically or epigenetically, lead to multigenetic phenotypic abnormalities including cancer. Imprinted genes may also mechanistically link nutritional perturbations like methylation deficiency directly to the etiology of cancer because their cis-acting regulatory elements are epigenetically labile. We propose to use phylogenetic comparisons of orthologous sequences from members of the three extant mammalian orders, Prototheria, Metatheria and Eutheria to characterize the evolution of imprinted domain structures and define the fundamental cis-acting imprint regulatory elements that epigenetically distinguish the parental alleles and also constitute targets for epigenetic dysregulation. The overall hypothesis of this grant application is that gene promoter silencing represents the primordial imprint mechanism, and that ongoing interparental genetic conflict has led to increased regulatory complexity for some imprinted domains, as the maternal and paternal genomes evolved counteracting strategies to overcome gene repression. Imprinting mechanisms are therefore postulated to be less complex in more ancestral mammals. To test this novel hypothesis we recently produced bacterial artificial chromosome (BAC) libraries from the imprinted opossum (Didelphus virginiana) and the non-imprinted platypus (Ornithorhynchus anatinus) to examine imprinted domains containing genes involved in cancer that are regulated by three different imprinting mechanisms. Maternal repression of expression will be modeled by NNAT (Neuronatin); paternal repression of expression with antisense transcripts will be modeled by M6P/IGF2R, and reciprocal parental repression of juxtapositioned genes by an intervening imprint center will be modeled by the IGF2/H19 and DLK1/MEG3 imprinted domains. We will test the functional relevance of novel regulatory elements identified in these comparisons by determining if they can direct acquisition of imprinting in transgenic mice. The successful completion of these comparative phylogenetic studies will significantly enhance our understanding of the evolution of this unique mammalian form of gene regulation. These studies will also be critical for identifying novel imprinted genes, and characterizing the less well-defined imprinted domains known to harbor genetic and/or epigenetic mutations mechanistically involved in cancer and neurogenetic disorders, such as schizophrenia, bipolar disease and autism.