Epigenetic Regulation of Kidney Development

描述（由申请人提供）：如何解释人类基因组以产生体内所有不同类型的细胞仍然是生物学和医学中的一个基本问题。尽管所有细胞都含有相同的基因，但细胞分化需要在高度特化的细胞中选择性地激活和抑制基因。如果不能正确调节这一基因选择过程，就会导致癌症、发育异常、细胞退化和许多其他疾病状态。细胞分化过程中的基因激活和抑制模式是由表观遗传机制指定的，这些机制是可遗传的，并受到修饰。真核染色质由包裹在组蛋白八聚体上的DMA组成。通过乙酰化、磷酸化、甲基化或泛素化对核心组蛋白尾部进行修饰可以显著改变局部染色质结构和基因表达的潜力。积累的生化和遗传证据表明，组蛋白H3和H4特定赖氨酸残基的甲基化可以决定一个基因是否仍然可被转录机制访问，或者它是否被沉默成紧密包装的异染色质。组蛋白的这种表观遗传修饰可以解释胚胎发育期间的遗传细胞记忆，并可以极大地影响病变和衰老细胞的基因表达模式。转录因子Pax2是肾脏发育所必需的，可以扩大注定成为肾脏的中胚层区域。Pax2具有早期发育开关的特性，有助于确定肾上皮细胞谱系。Pax蛋白从蠕虫到人类都是保守的，并直接结合DNA，但其作用机制尚不清楚。我们已经确定了一种叫做PTIP的蛋白质，它与Pax2的转激活结构域相互作用。如初步数据所述，PTIP是一种与组蛋白甲基转移酶（HMT）活性相关的必需蛋白。本课题将在多种遗传和生化系统中测试PTIP和Pax2在染色质表观遗传修饰中的功能。小鼠条件PTIP突变体和果蝇PTIP亚型将用于在体内测试PTIP的作用。生化纯化和基于细胞的组蛋白甲基转移酶检测将检测PTIP及其相关蛋白的活性。PTIP可能是发育调节因子（如Pax2）与决定和固定细胞谱系的表观遗传修饰机制之间的直接联系。

DESCRIPTION (provided by applicant): How the human genome is interpreted to generate all the diverse cell types in the body remains a fundamental question in biology and medicine. Even though all cells contain the same genes, cellular differentiation requires the selective activation and suppression of genes in highly specialized cells. Failure to correctly regulate this process of gene selectivity results in cancer, developmental abnormalities, cellular degeneration, and many other disease states. Gene activation and suppression patterns during cellular differentiation are specified by epigenetic mechanisms that are heritable and subject to modifications. Eukaryotic chromatin consists of DMA wrapped around a histone octamer. Modification of the core histone tails by acetylation, phosphorylation, methylation or ubiquitination can dramatically alter the local chromatin structure and the potential for gene expression. Accumulated biochemical and genetic evidence indicates that methylation at specific lysine residues of histones H3 and H4 can determine whether a gene remains accessible to the transcription machinery or whether it is silenced into tightly packaged heterochromatin. Such epigentic modifications of histones could account for a heritable cellular memory during embryonic development and could greatly affect gene expression patterns in diseased and aging cells. The transcription factor Pax2 is essential for kidney development and can expand the region of mesoderm fated to become kidney. Pax2 has the properties of an early developmental switch that helps to specify the kidney epithelial cell lineage. Pax proteins are conserved from worms to humans and bind DNA directly, yet their mechanisms of action remain obscure. We have identified a protein called PTIP that interacts with the transactivation domain of Pax2. As outlined in the preliminary data, PTIP is an essential protein that associates with histone methyltransferase (HMT) activity. In this proposal, the function of PTIP and Pax2 in epigenetic modification of chromatin will be tested in a variety of genetic and biochemical systems. Mouse conditional PTIP mutants and Drosophila PTIP hypomorphs will be used to test the role of PTIP in vivo. Biochemical purification and cell based histone methyltransferase assays will examine the activity of PTIP and its associated proteins. PTIP may be a direct link between developmental regulatory factors such as Pax2 and the mechanism of epigenetic modifications that determine and fix cell lineages.