The THO complex component Thp2 counteracts telomeric R-loops and telomere shortening

In human somatic cells or yeast cells lacking telomerase, telomeres are shortened upon each cell division. This gradual shortening of telomeres eventually leads to senescence. However, a small population of telomerase-deficient cells can survive by bypassing senescence through the activation of alternative recombination pathways to maintain their telomeres. Although genes involved in telomere recombination have been identified, mechanisms that trigger telomere recombination are less known. The THO (suppressor of the transcriptional defects of Hpr1 mutants by overexpression) complex is involved in transcription elongation and mRNA export. Here we demonstrate that mutations in THO complex components can stimulate early senescence and type II telomere recombination in cells lacking telomerase. The accumulation of telomere-associated noncoding telomere repeat-containing RNA (TERRA) is required for the observed telomere effects in THO complex mutants; reduced transcriptional efficiency, or overexpression of RNase H or C 1-3 A RNA can severely impair the type II telomere recombination. The results highlight a unique function for telomere-associated TERRA, in the formation of type II survivors. Moreover, because TERRA is a long noncoding RNA, these results reveal a function for long noncoding RNA in regulating recombination.

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“…While this work was under review for publication, two papers also published similar conclusions (46,47).…”

Section: Methodsmentioning

confidence: 77%

Telomeric transcripts stimulate telomere recombination to suppress senescence in cells lacking telomerase

Yu¹,

Kao

Lin

2014

Proc. Natl. Acad. Sci. U.S.A.

109

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“…The THO complex is involved in RNA maturation 18 and its presence at telomeres suggests roles in TERRA biogenesis. We were so far unable to confirm this notion for human TERRA but our laboratory has recently obtained data in S. cerevisiae, which demonstrate that telomere association of THO is conserved in yeast and that THO removes DNA-RNA hybrids from yeast telomeres 19 .…”

Section: Discussionmentioning

confidence: 85%

“…THO has roles in mRNP biogenesis, connecting transcription elongation with RNA maturation and nuclear export, and preventing genetic instability 18 . Its function in the regulation of the long noncoding RNA TERRA at telomeres and telomere stability in Saccharomyces cerevisiae is characterized in a separate paper 19 . We validated the presence of the human Thoc1 subunit at telomeres in chromatin immunoprecipitation (ChIP) experiments with an antibody (Fig.…”

Section: Implementation Of Qtipmentioning

confidence: 99%

A quantitative telomeric chromatin isolation protocol identifies different telomeric states

et al. 2013

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Telomere composition changes during tumourigenesis, aging and in telomere syndromes in a poorly defined manner. Here we develop a quantitative telomeric chromatin isolation protocol (QTIP) for human cells, in which chromatin is cross-linked, immunopurified and analysed by mass spectrometry. QTIP involves stable isotope labelling by amino acids in cell culture (SILAC) to compare and identify quantitative differences in telomere protein composition of cells from various states. With QTIP, we specifically enrich telomeric DNA and all shelterin components. We validate the method characterizing changes at dysfunctional telomeres, and identify and validate known, as well as novel telomere-associated polypeptides including all THO subunits, SMCHD1 and LRIF1. We apply QTIP to long and short telomeres and detect increased density of SMCHD1 and LRIF1 and increased association of the shelterins TRF1, TIN2, TPP1 and POT1 with long telomeres. Our results validate QTIP to study telomeric states during normal development and in disease.

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“…The existence of telomeric R-loops has been recently shown in budding yeast in two independent studies. Interestingly, those telomeric R-loops were significantly increased in THO mutants, which suffer from short telomeres (Pfeiffer et al 2013), indicating that proper TERRA biogenesis is important for telomere maintenance. Noticeably, THO subunits were identified at A. Aguilera and H. Gaillard human telomeres as well .…”

Section: Telomeres As a Putative Region Prone To Terra-mediated Tarmentioning

confidence: 99%

Transcription and Recombination: When RNA Meets DNA

Aguilera

Gaillard

2014

Cold Spring Harbor Perspectives in Biology

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Correspondence: aguilo@us.es A particularly relevant phenomenon in cell physiology and proliferation is the fact that spontaneous mitotic recombination is strongly enhanced by transcription. The most accepted view is that transcription increases the occurrence of double-strand breaks and/or singlestranded DNA gaps that are repaired by recombination. Most breaks would arise as a consequence of the impact that transcription has on replication fork progression, provoking its stalling and/or breakage. Here, we discuss the mechanisms responsible for the cross talk between transcription and recombination, with emphasis on (1) the transcription -replication conflicts as the main source of recombinogenic DNA breaks, and (2) the formation of cotranscriptional R-loops as a major cause of such breaks. The new emerging questions and perspectives are discussed on the basis of the interference between transcription and replication, as well as the way RNA influences genome dynamics.H omologous recombination (HR) is a conserved pathway responsible for the repair of double-strand breaks (DSBs). In mitotic cells, DSBs may be induced by genotoxic agents, such as g irradiation or may occur spontaneously, in most of the cases in association with replication. Although HR represents one of the two main mechanisms of DSB repair, the other being nonhomologous end joining (NHEJ), eukaryotic cells favor HR as the preferential DSB repair pathway during the S/G 2 phases of the cell cycle, when the sister chromatid is available as template for error-free repair. Thus, HR events are regulated at different steps along the cell cycle, among others by the cyclin-dependent kinase 1 during 5 0 -end resection to guarantee its occurrence at S/G 2 (Heyer et al. 2010;Huertas 2010). Consequently, spontaneous mitotic recombination events are generally interpreted as the result of DSB repair during S/G 2 , although it cannot be disregarded that recombination could also be initiated by singlestranded DNA (ssDNA) gaps generated during replication.Spontaneous mitotic recombination might, in principle, take place anywhere in the genome with similar probability. However, as for mutations, both recombination and chromosome breakages occur more frequently in particular regions, referred to as hot spots. Those hot spots might arise from different local features, including the formation of non-B secondary structures, chromatin compaction, DNA-protein barriers to replication, or low-replication initi- . Nevertheless, the most extended and physiological relevant feature enhancing the probability of recombination is likely to be transcription (Aguilera 2002;Kim and Jinks-Robertson 2012;Gaillard et al. 2013). From bacteria to humans, a large body of evidence has accumulated showing that transcription stimulates spontaneous recombination, a phenomenon referred to as transcription-associated recombination (TAR). As replication failures seem to be the main source of recombinogenic DSBs, our actual view is that the major mechanism by which transcription stimulates recom...

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The THO complex component Thp2 counteracts telomeric R-loops and telomere shortening

Cited by 128 publications

References 49 publications

Telomeric transcripts stimulate telomere recombination to suppress senescence in cells lacking telomerase

Telomeric transcripts stimulate telomere recombination to suppress senescence in cells lacking telomerase

A quantitative telomeric chromatin isolation protocol identifies different telomeric states

Transcription and Recombination: When RNA Meets DNA

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