Deciphering the regulation of germline ribosomal DNA maintenance

About This Grant

Project summary Protein synthesis is one of the most essential functions of all cells, so it is crucial that cells generate sufficient ribosomes to support robust protein production. In order to transcribe sufficient ribosomal RNAs (rRNAs) to sustain ribosome biogenesis, eukaryotic genomes consequently harbor hundreds of copies of rRNA sequences arranged in tandemly duplicated clusters called ribosomal DNA (rDNA). Curiously, the repetitive nature of these rDNA loci makes them inherently unstable and the number of rRNA sequence copies within an rDNA locus can decrease over time. Consequently, rDNA instability is associated with organismal aging and many diseases. Still, these unstable rDNA loci are maintained throughout populations by germline mechanisms that restore lost rDNA copies to ensure sufficient rDNA is inherited at each generation. Despite the importance of this germline rDNA maintenance to indefinitely propagate the genome, the cellular processes that accomplish rDNA restoration remain unknown. Unravelling these mechanisms that neutralize rDNA instability is crucial to fully comprehending the role of rDNA instability in aging and human health, however, the repetitiveness of these loci have made them largely difficult to study in most organisms. My lab has capitalized on using Drosophila rDNA deletion mutants and their convenient phenotypes to establish a system to rapidly investigate the genetic requirements for rDNA restoration activity. Using this system we have revealed that activation of the rDNA-specific retrotransposon R2 initiates germline rDNA expansion and that this activity is regulated by mTor signaling, securing a grasp on the first valuable threads needed to unravel the processes that govern rDNA maintenance. Over the next five years, my lab will capitalize on these foundational discoveries and the uniquely tractable system we have established to reveal how mTor activity directs germline rDNA copy number maintenance. In particular, we will seek to understand how rDNA copy number is sensed and in turn affects mTor activity, and how mTor directs transcription at rDNA loci to control expression of the R2 copies that are embedded within rDNA. Accomplishing these goals revealing how rDNA maintenance is orchestrated in the Drosophila germline will enable our future studies to directly investigate the impact of rDNA instability on organismal aging and serve as an entry point to study the mechanisms that maintain more complex rDNA in other organisms.