Links between nucleolar activity, rDNA stability, aneuploidy and chronological aging in the yeast Saccharomyces cerevisiae

Abstract

The nucleolus is speculated to be a regulator of cellular senescence in numerous biological systems (Guarente, Genes Dev 11(19):2449–2455, 1997; Johnson et al., Curr Opin Cell Biol 10(3):332–338, 1998). In the budding yeast Saccharomyces cerevisiae, alterations in nucleolar architecture, the redistribution of nucleolar protein and the accumulation of extrachromosomal ribosomal DNA circles (ERCs) during replicative aging have been reported. However, little is known regarding rDNA stability and changes in nucleolar activity during chronological aging (CA), which is another yeast aging model used. In the present study, the impact of aberrant cell cycle checkpoint control (knock-out of BUB1, BUB2, MAD1 and TEL1 genes in haploid and diploid hemizygous states) on CA-mediated changes in the nucleolus was studied. Nucleolus fragmentation, changes in the nucleolus size and the nucleolus/nucleus ratio, ERC accumulation, expression pattern changes and the relocation of protein involved in transcriptional silencing during CA were revealed. All strains examined were affected by oxidative stress, aneuploidy (numerical rather than structural aberrations) and DNA damage. However, the bub1 cells were the most prone to aneuploidy events, which may contribute to observed decrease in chronological lifespan. We postulate that chronological aging may be affected by redox imbalance-mediated chromosome XII instability leading to both rDNA instability and whole chromosome aneuploidy. CA-mediated nucleolus fragmentation may be a consequence of nucleolus enlargement and/or Nop2p upregulation. Moreover, the rDNA content of chronologically aging cells may be a factor determining the subsequent replicative lifespan. Taken together, we demonstrated that the nucleolus state is also affected during CA in yeast.Electronic supplementary materialThe online version of this article (doi:10.1007/s10522-014-9499-y) contains supplementary material, which is available to authorized users.

Single-cell analysis of aneuploidy events using yeast whole chromosome painting probes (WCPPs)

“…4E). This is also in agreement with our previous observation that nucleolus is fragmented during chronological ageing in yeast and multiple chromosome XIIspecific signals may be documented (Lewinska et al, 2014).…”

“…The WCPP-based system was validated using disomic yeast cells with introduced disomy (cells with disomic chromosomes I, II, V, X and XII) (Torres et al, 2010). Discrimination between "normal" and aberrant signals was possible both with and without cell synchronisation, which agrees with our previous results on chronological ageing-mediated aneuploidy in budding yeast (Lewinska et al, 2014). Moreover, we were able to characterise typical and cell cycle phase-dependent signal shapes, after DNA cell cycle analysis, such as chromosome XII.…”

Stratification of yeast cells during chronological aging by size points to the role of trehalose in cell vitality

“…If trehalose interferes with aberrant protein refolding, it might in fact lead mother cells to segregate the damaged proteins into daughters. There is a well-documented concept of asymmetrical inheritance in replicative aging, where an aged mother during cell division selectively keeps damaged molecules to itself while generating a rejuvenated daughter cell (Lai et al 2002; Jazwinski 2005; Henderson and Gottschling 2008; Zadrag-Tecza et al 2009; Klinger et al 2010, Nystrom and Liu 2014, Lewinska et al 2014). In contrast, in chronological aging, this asymmetry is apparently reversed, as our results show.…”

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

“…In S. cerevisiae , the rDNA stability is suggested to regulate both replicative and chronological aging [26–28]. Sir2 and Fob1 play opposite role in rDNA recombination, i.e.…”

“…Sir2 inhibits, while Fob1 promotes rDNA recombination [29]. Multimer ERC accumulation is significantly enhanced in mutants that have aberrant cell cycle checkpoint control during chronological aging [26]. Sgs1 is a DNA helicase, whose deletion causes much higher gene mutation frequency and gross chromosomal rearrangement (GCR) frequency than wild-type cells during chronological aging [22], but does not result in elevated level of ERCs [30–32].…”