Yeast Npl3 regulates replicative senescence outside of TERRA R-loop resolution and co-transcriptional processing

Area of Science:

• * Molecular Biology
• * Genetics
• * Cell Biology

Background:

• Eukaryotic cells without telomerase exhibit telomere shortening, leading to replicative senescence.
• Telomerase RNA (TERRA) expression increases during senescence in yeast lacking the telomerase RNA template (TLC1).
• Npl3, an RNA-processing protein, influences telomere maintenance and its deletion exacerbates senescence in telomerase-deficient cells.

Purpose of the Study:

• To investigate the role of Npl3 in regulating TERRA expression and telomere homeostasis.
• To elucidate the mechanisms by which Npl3 impacts cellular senescence.

Main Methods:

• Genetic manipulation in yeast models, including gene deletions (tlc1Δ, npl3Δ, dot1Δ) and analysis of recombination.
• Measurement of TERRA levels and assessment of cell cycle arrest and senescence phenotypes.
• Investigation of Npl3's interaction with RNA:DNA hybrid resolution pathways (RNase H1/H2) and the THO/TREX complex.

Main Results:

• Npl3 deletion accelerates senescence in tlc1Δ yeast and significantly increases TERRA levels.
• Npl3 does not appear to resolve TERRA RNA:DNA hybrids via RNase H1/H2 pathways, and Rad52 remains essential for senescence escape.
• Npl3 functions independently of the THO/TREX pathway for RNA processing, but Dot1 deletion rescues the accelerated senescence phenotype in npl3Δ cells.

Conclusions:

• Npl3 plays a critical role in regulating cellular senescence beyond its known functions in RNA processing and RNA:DNA hybrid resolution.
• Npl3's function in telomere maintenance is linked to telomere tethering at the nuclear periphery, potentially involving Dot1.
• This study reveals a novel role for Npl3 in preventing premature senescence through mechanisms independent of established pathways.