The makings of TERRA R-loops at chromosome ends

Telomeres protect chromosome ends from nucleolytic degradation, uncontrolled recombination by DNA repair enzymes and checkpoint signaling, and they provide mechanisms for their maintenance by semiconservative DNA replication, telomerase and homologous recombination. The telomeric long noncoding RNA...

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Bibliographic Details
Published in:Cell cycle (Georgetown, Tex.) Tex.), 2021-09, Vol.20 (18), p.1745-1759
Main Authors: Fernandes, Rita Valador, Feretzaki, Marianna, Lingner, Joachim
Format: Article
Language:English
Subjects:
Animals
Cell Cycle
DNA - metabolism
homologous recombination
Humans
Neoplasms - metabolism
R-Loop Structures
R-loops
RAD51
Rad51 Recombinase - metabolism
Recombinational DNA Repair
Repetitive Sequences, Nucleic Acid
Review
RNA, Long Noncoding - metabolism
Shelterin Complex - metabolism
shelterin proteins
Signal Transduction
Telomerase - metabolism
Telomere Homeostasis
Telomere Shortening
Telomeres
TERRA
Transcription, Genetic
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Summary:Telomeres protect chromosome ends from nucleolytic degradation, uncontrolled recombination by DNA repair enzymes and checkpoint signaling, and they provide mechanisms for their maintenance by semiconservative DNA replication, telomerase and homologous recombination. The telomeric long noncoding RNA TERRA is transcribed from a large number of chromosome ends. TERRA has been implicated in modulating telomeric chromatin structure and checkpoint signaling, and in telomere maintenance by homology directed repair, and telomerase - when telomeres are damaged or very short. Recent work indicates that TERRA association with telomeres involves the formation of DNA:RNA hybrid structures that can be formed post transcription by the RAD51 DNA recombinase, which in turn may trigger homologous recombination between telomeric repeats and telomere elongation. In this review, we describe the mechanisms of TERRA recruitment to telomeres, R-loop formation and its regulation by shelterin proteins. We discuss the consequences of R-loop formation, with regard to telomere maintenance by DNA recombination and how this may impinge on telomere replication while counteracting telomere shortening in normal cells and in ALT cancer cells, which maintain telomeres in the absence of telomerase.
ISSN:1538-4101
1551-4005
DOI:10.1080/15384101.2021.1962638