Rejuvenation of ribosomal RNA gene repeats at the nuclear pore

The ribosomal RNA genes (rDNA) exist as tandem repeats in eukaryotes and are, therefore, highly unstable. Each rDNA unit includes a replication fork barrier site to avoid collisions between DNA replication forks and transcriptional machinery. However, because of this barrier, DNA double-strand breaks are induced at a relatively high frequency. If damage is repaired by the homologous recombination in rDNAs, it may result in frequent copy number changes and the production of extrachromosomal ribosomal DNA circles, both of which are closely linked to the regulation of lifespan. Here, we review recent progress in elucidating a multi-layered repair process of rDNA that occurs in the nucleolus, nucleoplasm and nuclear pores. Binding to nuclear pores appears to be the final strategy for repairing any remaining damage to the rDNA. Here, we propose the possible contribution of nuclear pores to the asymmetric distribution of damaged rDNA between mother and daughter cells as well as its possible impact on aging/rejuvenation.