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展和疾病都是至关重要的。多细胞生物在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会导致发育缺陷和癌症等疾病。剂量补偿是一种特殊的基因调节形式，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。在线虫体内，剂量补偿是通过凝集素样剂量补偿复合体(DCC)完成的，它结合了XX两性的两条X染色体，使基因表达减半。凝聚素因其在有丝分裂和减数分裂过程中包装和分离染色体的作用而广为人知。然而，来自多个系统的证据表明，凝聚素也参与了基因表达的调节。目前尚不清楚DCC以及凝聚素是如何调控基因表达的。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从机制上联系起来的。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转变的时候建立的，以及随后如何维持抑制。该方案验证了剂量补偿功能的假设，即通过重新招募染色质修饰复合体，在剂量补偿的X染色体上放置一组染色质标记。这些染色质修饰建立了一个染色质环境，这抑制了RNA聚合酶II的结合，并导致聚合酶在早期伸长过程中停滞不前。该建议还旨在通过研究转录机制在剂量补偿过程中是如何受到影响的，来阐明转录调控的机制。最后，通过研究剂量补偿介导的染色质标记在各种具有分化缺陷的突变体中出现的时间，通过研究触发剂量补偿的基因在早期发育中是如何调节的，以及通过使用条件突变体在初始敏感期之后关闭DCC功能，该建议还研究了DCC介导的抑制是如何启动和维持的。

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.