A genome-wide screen identifies genes that suppress the accumulation of spontaneous mutations in young and aged yeast cells

Abstract

To ensure proper transmission of genetic information, cells need to preserve and faithfully replicate their genome, and failure to do so leads to genome instability, a hallmark of both cancer and aging. Defects in genes involved in guarding genome stability cause several human progeroid syndromes, and an age-dependent accumulation of mutations has been observed in different organisms, from yeast to mammals. However, it is unclear if the spontaneous mutation rate changes during aging, and if specific pathways are important for genome maintenance in old cells. We developed a high-throughput replica-pinning approach to screen for genes important to suppress the accumulation of spontaneous mutations during yeast replicative aging. We found 13 known mutation suppression genes, and 31 genes that had no previous link to spontaneous mutagenesis, and all acted independently of age. Importantly, we identified PEX19, encoding an evolutionarily conserved peroxisome biogenesis factor, as an age-specific mutation suppression gene. While wild-type and pex19{Delta} young cells have similar spontaneous mutation rates, aged cells lacking PEX19 display an elevated mutation rate. This finding suggests that functional peroxisomes are important to preserve genome integrity specifically in old cells, possibly due to their role in reactive oxygen species metabolism.\n\nAuthor SummarySpontaneous mutations arise as a consequence of improper repair of DNA damage caused by intracellular (i.e. toxic by-products of normal cellular metabolism or inaccurate DNA replication) or external (e.g. UV light or chemotherapy) sources. Elevated mutagenesis is implicated in tumorigenesis, and an age-dependent accumulation of mutations has been observed in many organisms. However, it is still unclear how and at which rate mutations accumulate during aging. It is also unknown if specific mechanisms exist that protect the genome of aged cells. We developed a high-throughput, genome-wide approach to identify genes that suppress the accumulation of mutations during yeast replicative aging. Yeast replicative aging refers to the decline in viability a single cell experiences with increasing number of mitotic divisions. We identified a number of new genes that counteract the accumulation of mutations independently of age. Moreover, we discovered that PEX19, a gene involved in the biogenesis of peroxisomes, is important to prevent the accumulation of mutations in aged cells. Since PEX19 is conserved in humans, our work might help understand how human cells could better protect their genome from mutations during aging.