Project 458662

The preservation of genetic material is essential for cell proliferation and survival. Unstable or damaged DNA can result in mutations and subsequently contribute to diseases which include a multitude of human cancers. The nucleolus is a sub-compartment of the nucleus typically associated with ribosome biogenesis. However, recent studies have suggested that the nucleolus is also involved in maintaining genome stability. Nucleoli contain repeats of ribosomal DNA (rDNA) genes that encode ribosomal RNA, a key component of the ribosome. The rDNA genes are highly susceptible to DNA damage and replication stress due to their repetitive sequences and high frequency of transcription; consequently, the rDNA locus is a known chromosome recombination hotspot in lung and colorectal cancers. Notably, DNA double-strand breaks (DSBs) within rDNA result in nucleoli and rDNA reorganizing into cap structures at the nucleolar periphery. This nucleolar reorganization and cap formation is thought to facilitate efficient repair of DSBs and requires the nucleolar protein TCOF1. Cells that lack TCOF1 are unable to form cap structures and do not efficiently recruit DNA damage response proteins that are required for DSB resolution, ultimately resulting in genome instability and cell death. The goal of our project is to understand how and why TCOF1 is required for nucleolar cap formation and DSB repair utilizing both a proteomics and genetics approach. Altogether, our work aims to elucidate how the nucleolar protein TCOF1 maintains genome stability within nucleoli. Understanding the regulation of DNA damage at the highly repetitive and important rDNA can provide insight into how cells prevent chromosomal aberrations that can cause carcinogenesis.