Chromosome inverted fusions, dicentrics and genome instability

描述(申请人提供)：基因组重排是细胞染色体的改变，可导致病理改变。基因组重排普遍存在于细胞中，由细胞复制错误引起。一种称为大规模重排的类型对细胞特别有害；它可以改变某些基因的数量，可以突变基因，还可以产生持续重排的不稳定染色体。很明显，在人类中，大规模重排确实会导致重大的病理变化，最著名的例子是费城的染色体，在那里，Chr22和Ch9的部分融合，形成了导致白血病的基因融合。最近对癌症基因组的深度测序揭示了一系列令人眼花缭乱的大规模变化；在一些染色体中，似乎发生了爆炸，然后随机拼凑起来，在另一些染色体中，有染色体链连接在一起。正如前面提到的，大规模的重排也形成了固有的不稳定的染色体，包括包含两个着丝粒的双着丝粒，因此是不稳定的。一种特殊的重排在胰腺癌细胞中出现的频率很高。这被称为折返倒位，染色体与自身融合，形成双着丝粒。为什么我们对折回反转特别感兴趣？我们开发了一种发芽酵母染色体不稳定系统，使我们能够研究大规模重排。我们现在已经在酵母中鉴定出一种折回倒置型染色体变化(我们称之为倒置融合)，它确实形成了双着丝粒。这种融合似乎经常发生在酵母基因组中，尽管我们还不知道在哪里或以多大的频率发生。我们研究了这种酵母反向融合/折叠反向转化的形成机制，并提出了一个可以检验的模型。在这项提案中，我们将在酵母中鉴定融合形成双着丝粒的序列。这将提供有关融合在人类基因组中可能有多常见的信息。我们将研究融合是如何发生的，这对于了解胰腺细胞如何发生融合以及在正常人类细胞中如何避免融合很重要。最后，我们将在分裂酵母和人类细胞中建立遗传系统来研究折叠倒置。这将使我们开始直接了解折叠反转类型的重排是如何在胰腺癌中发生的。

DESCRIPTION (provided by applicant): Genome rearrangements are changes to cells chromosomes that can cause pathology. Genome rearrangements common in cells, and arise due to errors in cell duplication. One type, called a large scale rearrangement, is particularly deleterious to a cell; it can change the number of certain genes, can mutate a gene, and can generate unstable chromosomes that continue to rearrange. In humans it is clear that large scale rearrangements indeed cause significant pathology, a most famous case being the Philadelphia Chromosome where parts of Chr22 and Ch9 fuse, forming a gene fusion that causes leukemia. Recent deep sequencing of cancer genomes reveals a bewildering array of large scale changes; in some chromosomes appear to have exploded and pieced back together randomly, in others there are chains of chromosomes joined together. As mentioned, large scale rearrangements also form inherently unstable chromosomes, including dicentrics that contain two centromeres and are thus unstable. One particular rearrangement arises at a high frequency in pancreatic cancer cells. It's called a fold back inversion, where a chromosome fuses with itself such that it should form a dicentric. Why are fold back inversions of particular interest to us? We have developed a budding yeast chromosome instability system allows us to study large scale rearrangements. We have now identified a fold back inversion type chromosome change (that we call an inverted fusion), in yeast, that indeed forms dicentrics. Such fusions appear to occur frequently in the yeast genome, though we do not yet know where or how frequently. We have studied the mechanism of how this yeast inverted fusion/fold back inversion forms, and propose a model we can test. In this proposal, we will identify sequences in yeast that fuse to form dicentrics. This will provide information on how common fusions may be in the human genome. We will study how fusions occur, important for knowing how fusions occur in pancreatic cells and how they are avoided in normal human cells. Finally, we will establish genetic systems in fission yeast and in human cells to study fold back inversions. This will allow us to begin to directly understand how foldback inversion types of rearrangements arise in pancreatic cancer.