Telomere shortening causes distinct cell division regimes during replicative senescence in Saccharomyces cerevisiae

Abstract

Background Telomerase-negative cells have limited proliferation potential. In these cells, telomeres shorten until they reach a critical length and induce a permanently arrested state. This process called replicative senescence is associated with genomic instability and participates in tissue and organismal ageing. Experimental data using single-cell approaches in the budding yeast model organism show that telomerase-negative cells often experience abnormally long cell cycles, which can be followed by cell cycles of normal duration, before reaching the terminal senescent state. These series of non-terminal cell cycle arrests contribute to the heterogeneity of senescence and likely magnify its genomic instability. Due to their apparent stochastic nature, investigating the dynamics and the molecular origins of these arrests has been difficult. In particular, whether the non-terminal arrests series stem from a mechanism similar to the one that triggers terminal senescence is not known. Results Here, we provide a mathematical description of sequences of non-terminal arrests to understand how they appear. We take advantage of an experimental data set of cell cycle duration measurements performed in individual telomerase-negative yeast cells that keep track of the number of generations since telomerase inactivation. Using numerical simulations, we show that the occurrence of non-terminal arrests is a generation-dependent process that can be explained by the shortest telomere reaching a probabilistic threshold length. While the onset of senescence is also triggered by telomere shortening, we highlight differences in the laws that describe the number of consecutive arrests in non-terminal arrests compared to senescence arrests, suggesting distinct underlying mechanisms and cellular states. Conclusions Replicative senescence is a complex process that affects cell divisions earlier than anticipated, as exemplified by the frequent occurrence of non-terminal arrests early after telomerase inactivation. The present work unravels two kinetically and mechanistically distinct generation-dependent processes underlying non-terminal and terminal senescence arrests. We suggest that these two processes are responsible for two consequences of senescence at the population level, the increase of genome instability on the one hand, and the limitation of proliferation capacity on the other hand.

Individual cell fate and population dynamics revealed by a mathematical model linking telomere length and replicative senescence

“…The mathematical model is largely based on our data from single cell lineages observed in microfluidic experiments and accounts for a number of already well-characterized types of cell-to-cell variability, as described in ( 16, 18, 24 ). In the microfluidic experiments, the consecutive cell cycle durations are measured from telomerase inactivation to cell death in individual cell lineages (Fig.1B-C).…”

“…S1B-D). The probabilities to exit a sequence of arrests (𝑝 /.0-&/ and 𝑝 ).-( 1) were assumed to be constant, as demonstrated (24). For senescence onset, 𝑝 ,.'…”

“…We used S. cerevisiae, in which telomerase can be inactivated, as a well-documented experimental model of replicative senescence (25)(26)(27). We thus exploited the wealth of information and molecular models derived from S. cerevisiae regarding telomere shortening pathways, the molecular mechanism underlying replicative senescence, and the data from single-cell lineages in microfluidics experiments (11,14,16,18,23,24), to track in depth the state of each individual cell of the population, including the length of each telomere over time. We managed to delineate hidden components of replicative senescence mechanism beyond the scope of experimental observations.…”

“…Specifically, a subset of individual cells, so-called type B cells, undergo several switches between non-terminal arrests and normal proliferation prior to terminal senescence, in contrast to type A cells, which undergo the switch in a single step. Even though both terminal and non-terminal arrests are abnormally long cycles associated with the activation of the DNA damage checkpoint, their manifestation corresponds to distinct probability laws, thus possibly arising from distinct molecular origins ( 23, 24 ). In non-terminal arrests of type B cells, the cells either recover upon repair of a damage, presumably stemming from a yet unidentified telomere defect, or adapt to the damage, forcing mitosis until successful repair.…”

Senescence-associated secretory phenotypes in rat-derived dedifferentiated fat cells with replicative senescence

“…Indeed, other researchers have reported that replicative senescence can be distinguished from induced senescence by analyzing rDNA or methylation of its promoter 41) . Telomerase shortening, the main phenotype of cell replication, is thought to be the main trigger for inducing replicative senescence 42,43) . Recently, various studies have shown that telomere shortening causes constant DNA damage response, leading to stress-induced premature senescence 44) .…”