Mechanisms of X chromosome dosage compensation in C. elegans

New York University, New York NY

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Abstract

DESCRIPTION (provided by applicant): Regulation of chromosome structure is important for normal cell function and is often disrupted in disease. Condensins are evolutionarily conserved, multi-subunit protein complexes that are essential for chromosome condensation and segregation during cell division and play key roles in transcription regulation and DNA repair. Most organisms contain two types of condensins, which perform different functions and localize to different chromosomal regions. C. elegans contains a third type of condensin that specifically binds to and represses X chromosome transcription to accomplish dosage compensation within the dosage compensation complex (DCC). It is not known how condensins are targeted to their binding sites, and how they regulate chromosome structure and transcription. Our goal is to address this significant gap in our knowledge by determining the mechanism of DCC binding and function in C. elegans. C. elegans DCC serves as an excellent experimental model to study condensin binding and function. DCC is recruited specifically to the X chromosome and represses transcription of both X chromosomes in XX hermaphrodites to equalize overall X-linked transcript levels to that of XO males. DCC is first targeted to X- specific recruitment site, and then spreads onto physically connected chromatin. Spreading gives rise to ~90% of the DCC binding sites along the X. Majority of these sites are at active gene promoters. There is no direct relationship between DCC binding and repression, thus DCC may regulate genes at long-range. Important gaps in our understanding of DCC mechanism is the relation between DCC binding and transcription at the local and global level, and the molecular mechanism by which the DCC spreads onto the chromosome. The objective of this application is to 1) test if DCC binding is sufficient and required for repression, 2) determine the role of H4K20me1 in DCC binding 3) determine how the DCC affects chromosome structure of the X. We will accomplish these objectives by analyzing the effects of ectopic DCC binding, DCC binding site deletions, X chromosome duplications and measure DCC localization, gene expression and chromosome structure genome-wide using ChIP-seq, RNA-seq and 4C-seq, respectively. At the completion of our project we will have a better understanding of a persistent question: how do condensins bind to chromosomes and affect its structure and function. This is relevant to health, because chromosome structure and condensin function is essential for proper chromosome segregation, transcription, and DNA repair, processes that are disrupted in cancers and developmental diseases.