Chromatin Diminution in Ascaris

描述（由申请人提供）：基因组的维持和稳定性是必不可少的，生物体的基因组很少发生变化。与此形成鲜明对比的是，染色质减少是一个程序化的过程，它从基因组中消除特定的DNA序列。在寄生线虫蛔虫中，25%的基因组在第3至第5次分裂（4至16个细胞阶段）期间在体细胞谱系中被消除，而种系基因组保持完整。重复和独特的序列（基因）在染色质减少过程中丢失。消除导致染色体断裂和染色体末端的丢失以及新染色体的产生。这一过程被认为是发育和生殖系建立所必需的一种基因沉默形式，但这种程序化消除如何有助于早期蛔虫发育中的生殖系向体细胞过渡，在发现100多年后仍然是一个谜。此外，染色体区域如何被靶向消除、染色体断裂的位点位于何处、DNA断裂如何产生、丢失了什么序列以及如何选择特定序列以丢失或保留的机制仍然未知。新的技术和方法将被用来利用蛔虫独特的生物学和工具来检查染色质减少并定义消除和重新排列的序列，检查与减少相关的染色质修饰，测试细胞分裂期间消除的DNA如何不分离的新假设，并获得对小RNA在染色质减少中的潜在作用的额外见解。我们建议，全面比较蛔虫的体细胞和生殖细胞基因组将使我们能够解决第一次的一些核心问题，包括减少：什么重排发生？哪些基因丢失了？断点之间是否有共同的特性，这些特性提供了对断点如何定义的深入了解？染色体断裂点是在所有个体中大致相同的位置，还是在不同个体中有所不同？此外，我们提出，表观遗传染色质的变化与减少的过程中，蛔虫22 G内切siRNA和相关的Argonaute CSR-1 RISC复合物有助于染色质减少标记区域的蛔虫染色体保留或消除。蛔虫是一种重要的人类病原体，因为它感染了超过10亿人。了解基因的维持，改变，以及改变在蛔虫基因表达中的作用，对于了解这种人类寄生虫的生物学非常重要。此外，了解减少的分子调节剂，机制和后果不仅可以深入了解DNA消除及其在线虫中的重要性，而且可能会增加我们对这种现象以及生殖系，染色体和基因组生物学的理解。 公共卫生相关性：寄生线虫在世界许多地方仍然是一个重大的公共卫生问题。仅蛔虫就感染了10亿多人，阻碍了流行地区的社会经济发展。我们将对蛔虫中一种不寻常的程序性DNA消除形式进行研究，即染色质减少，这在生物体的生物学中很重要。

DESCRIPTION (provided by applicant): Genome maintenance and stability are essential, and an organism's genome rarely changes. In striking contrast, chromatin diminution is a programmed process that eliminates specific DNA sequences from the genome. In the parasitic nematode, Ascaris, 25% of the genome is eliminated in the somatic lineages during the 3rd through 5th cleavage (4 to 16 cell stage), while the germline genome remains intact. Both repetitive and unique sequences (genes) are lost during chromatin diminution. The elimination results in chromosome breakage and the loss of chromosome termini as well as the generation of new chromosomes. This process is thought to be a form of gene silencing necessary for development and germline establishment, yet how this programmed elimination contributes to the germline to somatic transition in early Ascaris development remains a mystery more than 100 years after it was discovered. Furthermore, the mechanisms for how chromosomal regions are targeted for elimination, where the sites of chromosomal breakage are located, how DNA breaks are made, what sequences are lost, and how specific sequences are selected to be lost or retained remain unknown. New technologies and approaches will be leveraged to exploit the unique biology and tools in Ascaris to examine chromatin diminution and define eliminated and re-arranged sequences, to examine chromatin modifications associated with diminution, to test a new hypothesis for how eliminated DNA is not segregated during cell division, and to gain additional insight into the potential role of small RNAs in chromatin diminution. We propose that a comprehensive comparison of the somatic and germline genome in Ascaris will permit us to address for the first time a number of central questions regarding diminution including: What rearrangements occur? What genes are lost? Are there common features among the breakpoints that provide insight into how the breakpoints are defined? Are the chromosomal breakpoints at the same approximate location in all individuals or do they vary in different individuals? Furthermore, we propose that epigenetic chromatin changes are associated with the process of diminution and that Ascaris 22G endo-siRNAs and the associated Argonaute CSR-1 RISC complex contribute to chromatin diminution by marking regions of Ascaris chromosomes for retention or elimination. Ascaris is an important human pathogen as it infects over a billion people. Understanding gene maintenance, alterations, and the role of alterations in gene expression in Ascaris is important in understanding the biology of this human parasite. Furthermore, understanding the molecular regulators, mechanism, and consequences of diminution will not only provide insight into DNA elimination and its importance in nematodes, but is likely to increase our understanding of this phenomenon and germline, chromosome, and genome biology in general. PUBLIC HEALTH RELEVANCE: Parasitic nematodes remain a significant public health problem in many parts of the world. Ascaris alone infects upwards of 1 billion people and hinders socioeconomic development in endemic areas. We will carry out studies on an unusual form of programmed DNA elimination in Ascaris, chromatin diminution, important in the biology of the organism.