Both genome instability and replicative senescence stem from the shortest telomere in telomerase-negative cells

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• Telomere shortening in the absence of telomerase induces replicative senescence, a tumor suppressor mechanism.
• This senescence is paradoxically linked to oncogenic genomic instability, with the connecting mechanism being unclear.

Purpose of the Study:

• To elucidate the interplay between telomere dynamics, senescence, and genomic instability.
• To identify the threshold at which telomeres become dysfunctional and trigger senescence.

Main Methods:

• Developed a system in Saccharomyces cerevisiae to generate and track telomeres of precise lengths without telomerase.
• Employed single-telomere and single-cell analyses coupled with mathematical modeling.
• Utilized fluctuation assays to study genomic instability at the population level.

Main Results:

• Identified a critical telomere length threshold that triggers telomere dysfunction.
• A single shortest telomere below this threshold is sufficient to initiate replicative senescence.
• Genomic instability, specifically Pol32-dependent translocations, arises near the shortest telomere, leading to its re-elongation and potential senescence escape.

Conclusions:

• Telomere dysfunction serves as the mechanistic link between replicative senescence and genomic instability in telomerase-negative cells.
• This process initiates post-senescence survival pathways.
• The findings provide insight into tumor suppression and oncogenic processes.