RNA-DNA hybrids prevent resection at dysfunctional telomeres

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Telomeres shorten with each cell division, eventually triggering replicative senescence.
• TERRA RNA-DNA hybrids are known to play a role in homology-directed repair (HDR) at critically short telomeres.
• Transient telomeric RNA-DNA hybrids also form at longer telomeres, suggesting roles beyond HDR.

Purpose of the Study:

• To investigate the function of telomeric RNA-DNA hybrids at non-critically short telomeres.
• To determine the role of RNA-DNA hybrids in preventing or promoting telomere resection.
• To understand the dynamic regulation of TERRA RNA-DNA hybrids in cellular processes.

Main Methods:

• Utilized the temperature-sensitive cdc13-1 yeast mutant to control telomere resection.
• Assessed the impact of stabilizing or destabilizing RNA-DNA hybrids on single-stranded DNA (ssDNA) generation.
• Monitored cell viability in response to altered RNA-DNA hybrid levels.

Main Results:

• Telomeric RNA-DNA hybrids were found to prevent Exo1-mediated resection of telomeres.
• Stabilizing hybrids inhibited ssDNA generation, while destabilizing them augmented it.
• Cell viability of cdc13-1 mutants correlated with the presence or absence of RNA-DNA hybrids.
• Bulk telomere shortening rates were unaffected by telomeric hybrid levels.

Conclusions:

• Telomeric RNA-DNA hybrids act as a barrier to Exo1-mediated resection at non-functional telomeres.
• Dynamic regulation of TERRA RNA-DNA hybrids is essential; their presence may initiate HDR, while their removal permits resection.
• These findings reveal a novel role for telomeric hybrids in maintaining telomere integrity and regulating DNA repair pathways.