Tethering telomerase to telomeres increases genome instability and promotes chronological aging in yeast

Abstract

Chronological aging of the yeast Saccharomyces cerevisiae is attributed to multi-faceted traits especially those involving genome instability, and has been considered to be an aging model for post-mitotic cells in higher organisms. Telomeres are the physical ends of eukaryotic chromosomes, and are essential for genome integrity and stability. It remains elusive whether dysregulated telomerase activity affects chronological aging. We employed the CDC13-EST2 fusion gene, which tethers telomerase to telomeres, to examine the effect of constitutively active telomerase on chronological lifespan (CLS). The expression of Cdc13-Est2 fusion protein resulted in overlong telomeres (2 to 4 folds longer than normal telomeres), and long telomeres were stably maintained during long-term chronological aging. Accordingly, genome instability, manifested by accumulation of extra-chromosomal rDNA circle species, age-dependent CAN1 marker-gene mutation frequency and gross chromosomal rearrangement frequency, was significantly elevated. Importantly, inactivation of Sch9, a downstream kinase of the target of rapamycin complex 1 (TORC1), suppressed both the genome instability and accelerated chronological aging mediated by CDC13-EST2 expression. Interestingly, loss of the CDC13-EST2 fusion gene in the cells with overlong telomeres restored the regular CLS. Altogether, these data suggest that constitutively active telomerase is detrimental to the maintenance of genome stability, and promotes chronological aging in yeast.

Roles of Telomere Biology in Cell Senescence, Replicative and Chronological Ageing

“…Chronological lifespan is usually defined as the time period when cells remain viable at stationary phase (G 0 phase) [33]. The budding yeast post-mitotic cell ageing usually undergoes for 1–2 months of survival and has been widely used in ageing research [26,35,36,37,38,39,40,41,42]. It is believed that evolutionarily conserved key molecules in the polarization processes from yeast budding and mating to metazoan neuronal outgrowth and spinogenesis are homologous, potentially making the yeast chronological ageing process as a useful model for the non-dividing human cell ageing research [43,44,45,46,47,48,49].…”

“…More recently, no effect of long telomeres on vegetative cell division, meiosis or in cell chronological lifespan is observed in the yeast [57]. During chronological ageing, longer telomeres remain stable albeit without affecting chronological lifespan [42]. These strains with 2–4 folds longer telomeres do not carry any plasmids or gene deletions, potentially applicable to assess the relationship between overlong telomeres and chronological lifespan [42].…”

“…During chronological ageing, longer telomeres remain stable albeit without affecting chronological lifespan [42]. These strains with 2–4 folds longer telomeres do not carry any plasmids or gene deletions, potentially applicable to assess the relationship between overlong telomeres and chronological lifespan [42]. It thus appears that neither replicative nor chronological lifespan benefits from longer-than-normal telomeres.…”

“…Constitutive telomerase activity is observed by experimentally tethering the telomerase catalytic subunit Est2 to the single-stranded DNA binding protein Cdc13 with ectopic expression of the fusion gene CDC13-EST2 [42,87]. However, the constitutively increased telomerase activity results in shortened chronological lifespan [42].…”

Simultaneous visualisation of the complete sets of telomeres from the MmeI generated terminal restriction fragments in yeasts

“…One copy of RIF1 was deleted in BY4743 by a pRS306-rif1Δ cassette as descried previously (Liu et al, 2016;Wu et al, 2017). Rif1-5UTR-F & T7 and Rif1-orf-F& Rif1-orf-R were used to confirm RIF1 deletion.…”