Chromatin Diminution in Ascaris

描述(申请人提供)：基因组的维护和稳定至关重要，生物体的基因组很少发生变化。与之形成鲜明对比的是，染色质减少是一个程序化的过程，它会从基因组中消除特定的DNA序列。在寄生线虫中，25%的基因组在第三到第五次卵裂(4到16细胞期)期间在体细胞谱系中被消除，而种系基因组保持完整。在染色质减少的过程中，重复和独特的序列(基因)都会丢失。这种消除会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，但这种程序性消除是如何在蛔虫早期发育的生殖系向体细胞过渡的过程中发挥作用的，在它被发现100多年后仍然是一个谜。此外，如何将染色体区域作为消除的目标，染色体断裂的位置在哪里，DNA断裂是如何进行的，丢失了哪些序列，以及如何选择丢失或保留特定的序列，这些机制仍不清楚。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和定义消除和重新排列的序列，检查与减少相关的染色质修改，测试关于消除的DNA如何在细胞分裂过程中不分离的新假说，以及进一步了解小RNA在染色质减少中的潜在作用。我们建议，对蛔虫的体细胞和生殖系基因组进行全面的比较，将使我们能够第一次解决一些关于减数的核心问题，包括：发生了什么重排？哪些基因丢失了？断点之间是否有共同的特性可供深入了解断点是如何定义的？染色体断裂点在所有个体中是在相同的大致位置还是在不同的个体中有所不同？此外，我们认为表观遗传的染色质变化与染色质的减少过程有关，蛔虫22G Endo-siRNAs和相关的ArgAerte CSR-1 RISC复合体通过标记蛔虫染色体上的区域来保留或消除染色质的减少。蛔虫是一种重要的人类病原体，因为它感染了超过10亿人。了解蛔虫的基因维持、改变和基因表达改变的作用对于了解这种人类寄生虫的生物学很重要。此外，了解DNA减少的分子调控、机制和后果不仅有助于深入了解DNA消除及其在线虫中的重要性，而且可能增加我们对这一现象以及生殖系、染色体和基因组生物学的总体理解。 公共卫生相关性：在世界许多地区，寄生线虫仍然是一个严重的公共卫生问题。仅蛔虫一项就感染了超过10亿人，并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消除进行研究，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.