A two-step model for senescence triggered by a single critically short telomere

Area of Science:

• Cellular biology
• Genetics
• Molecular biology

Background:

• Telomeres protect chromosome ends from degradation and fusion.
• Progressive telomere shortening with replication leads to replicative senescence in the absence of telomere maintenance.
• The shortest telomere is a key factor influencing the timing of cellular senescence.

Purpose of the Study:

• To investigate the role of the shortest telomere in triggering cellular senescence.
• To identify the molecular mechanisms involved in pre-senescence cell division and senescence signaling.

Main Methods:

• Utilized telomerase-deficient cells with a single, very short telomere.
• Investigated the role of Mec1p-ATR, RAD52, and MMS1 in senescence.
• Analyzed cell division and telomere length dynamics before senescence.

Main Results:

• Cells with a single, very short telomere senesced earlier than controls.
• Mec1p-ATR specifically recognized the critically short telomere, initiating senescence.
• Cells underwent several divisions in a pre-senescence state, dependent on RAD52 and MMS1, without significant inter-telomeric recombination.

Conclusions:

• The length of the shortest telomere is a primary determinant of senescence onset.
• A RAD52-MMS1-dependent pathway maintains cells in a pre-senescence state.
• Mec1p-ATR signaling ultimately triggers senescence following telomere erosion.