Small RNA and whole chromosome recognition in Drosophila melanogaster.

描述(申请人提供)：真核生物使用一套表观遗传调控系统，这对基因组的稳定和正常的基因表达至关重要。表观遗传系统的破坏与广泛的病理有关，包括染色体不稳定、出生缺陷、癌症和发育异常。一种有趣的表观遗传调节类型，X染色体剂量补偿，调节X连锁基因在一个性别中的表达，以适应男性和女性不同数量的X染色体。剂量补偿在小鼠、线虫和果蝇中得到了广泛的研究。通常强调这些生物体在剂量补偿策略上的显著差异。然而，这三个系统都依赖于染色质调节复合体，它们被选择性地招募到X染色体上来调节表达。对这些络合物及其对染色质的作用进行了详细的研究。但在任何情况下，我们都不知道X染色质是如何被鉴定为具有必要的选择性的。我们的长期目标是了解整个染色体是如何识别和调控的。我们将检验的具体假设是，果蝇的X染色体识别涉及到小RNA。我们的研究表明，X染色体几乎独有的双向转录的卫星序列对一种有效的基因补偿修饰物做出反应。我们假设遗传修饰物是通过siRNA发挥作用的。拟议的实验将确定小RNA通路和X连锁卫星在剂量补偿中的作用。为了确定1)RNAi是否正常影响X染色质和剂量补偿，2)X连锁卫星是否是RNAi的来源和/或靶标，以及3)X连锁卫星是否有助于附近基因的剂量补偿，将寻求三个具体目标。我们认为，RNAi的作用先于或平行于先前发现的富含在X染色体上的元件，以确保对X染色质的唯一识别。

DESCRIPTION (provided by applicant): Eukaryotic organisms employ a suite of epigenetic regulatory systems that are essential for genome stability and normal gene expression. Disruptions in epigenetic systems are associated with a wide range of pathologies, including chromosome instability, birth defects, cancer and developmental abnormalities. An intriguing type of epigenetic regulation, X chromosome dosage compensation, adjusts the expression of X-linked genes in one sex to accommodate the different numbers of X chromosomes in males and females. Dosage compensation has been intensively studied in mice, C. elegans and Drosophila. The striking differences in the dosage compensation strategies of these organisms are usually emphasized. However, all three systems rely on chromatin regulatory complexes that are selectively recruited to the X chromosome to modulate expression. These complexes, and their actions on chromatin, have been studied in great detail. But in no case do we understand how X chromatin is identified with the requisite selectivity. Our long-term goal is to understand how an entire chromosome is identified and regulated. The specific hypothesis we will test is that X chromosome recognition in Drosophila involves small RNAs. Our studies reveal that bi-directionally transcribed satellite sequences that are near-exclusive to the X chromosome respond to a potent genetic modifier of compensation. We postulate that the genetic modifier exerts its effect through siRNA. The proposed experiments will determine the role of small RNA pathways and X-linked satellites in dosage compensation. Three specific aims will be pursued to determine if 1) RNAi normally influences X chromatin and dosage compensation, 2) if X-linked satellites are sources and/or targets of RNAi, and 3) if X- linked satellites contribute to the dosage compensation of genes situated nearby. We propose that RNAi acts prior to, or in parallel with previously identified elements, which are modestly enriched on the X chromosome, to ensure exclusive recognition of X chromatin.