The Dosage Compensation Machinery of C. Elegans

描述（由申请人提供）：基因表达的调节对健康发育和疾病都至关重要。多细胞生物体在其大多数体细胞中包含相同的遗传信息，但每个细胞表达一组独特的基因并采用不同的细胞命运。基因表达的异常调节导致发育缺陷和疾病，如癌症。剂量补偿是一种特殊形式的基因调控，影响整个染色体上的许多或大多数基因，以平衡性别之间的基因表达。在线虫秀丽隐杆线虫中，剂量补偿是通过一种缩合蛋白样剂量补偿复合物（DCC）完成的，该复合物结合XX两性体中的两条X染色体，使基因表达减半。凝聚素最为人所知的是其在有丝分裂和减数分裂期间包装和分离染色体的作用。然而，来自几个系统的证据表明，凝聚素也参与基因表达的调节。DCC和扩展的缩合蛋白如何调节基因表达尚不清楚。这个项目的长期目标是破译凝聚素的基因调控和有丝分裂染色体分离作用是如何机械相关的。这一建议旨在阐明蠕虫剂量补偿过程中凝聚作用的机制，它是如何在细胞从可塑性向分化过渡时建立的，以及随后如何维持阻遏。该提案测试了剂量补偿功能涉及通过招募染色质修饰复合物在剂量补偿的X染色体上放置一组染色质标记的假设。这些染色质修饰建立了染色质环境，其抑制RNA聚合酶II结合以及导致聚合酶在早期延伸期间停滞。该提案还旨在通过研究剂量补偿过程中转录机制如何受到影响来阐明转录调控机制。最后，该提案还调查了如何DCC介导的阻遏启动和维持，通过研究的时间出现的剂量补偿介导的染色质标记在各种突变体的分化缺陷，通过研究如何在早期发展的基因触发剂量补偿调节，并关闭DCC功能后，使用条件突变体的初始敏感期。

DESCRIPTION (provided by applicant): Regulation of gene expression is critical to both healthy development and disease. Multicellular organisms contain the same genetic information in most of their somatic cells, yet each cell expresses a unique set of genes and adopts a distinct cell fate. Aberrant regulation of expression of genes leads to developmental defects and diseases such as cancer. Dosage compensation is a specialized form of gene regulation affecting many, or most, genes on entire chromosomes, to balance gene expression between the sexes. In the worm Caenorhabditis elegans, dosage compensation is accomplished by a condensin-like dosage compensation complex (DCC), which binds both X chromosomes in XX hermaphrodites, to halve gene expression. Condensin is best known for its role in packaging and segregating chromosomes during mitosis and meiosis. However, evidence from several systems indicates that condensin is also involved in the regulation of gene expression. How the DCC, and by extension condensin, regulates gene expression is not known. The long-term goals of this project is to decipher how the gene regulatory and mitotic chromosome segregation roles of condensin are mechanistically related. This proposal is aimed at elucidating the mechanism of condensin-action during worm dosage compensation, how it is established at the time when cells transition from plasticity to differentiation, and how repression is maintained subsequently. The proposal tests the hypothesis that dosage compensation function involves placing a set of chromatin marks on dosage compensated X chromosomes, via recruitment of chromatin modifying complexes. These chromatin modifications set up a chromatin environment, which inhibits RNA polymerase II binding as well causes polymerase to stall during early elongation. The proposal also aims to elucidate the mechanism of transcription regulation by studying how the transcription machinery is affected during dosage compensation. Finally, the proposal also investigates how DCC-mediated repression is initiated and maintained, by studying the timing of appearance of dosage compensation mediated chromatin marks in various mutants with defects in differentiation, by studying how the gene triggering dosage compensation is regulated in early development, and by turning off DCC function after the initial sensitivity period using conditional mutants.