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Authors: Misino, Stefano
Title: Towards a mechanistic understanding of the role of TERRA in the alternative lengthening mechanism of telomeres
Online publication date: 22-Sep-2021
Language: english
Abstract: Telomeres are the nucleoprotein structures that shelter the chromosome ends from illegitimate repair and degradation. Due to the inability of replication to fully duplicate DNA molecules, telomeres shorten with every cell cycle, causing replicative senescence. To counteract telomere erosion, different mechanisms of telomere maintenance are adopted. The most common one is via telomerase, a reverse transcriptase that synthesizes de novo telomeric DNA. In the absence of telomerase, an alternative lengthening mechanism of telomeres, namely ALT, promotes telomere maintenance via homology-directed repair (HDR). Both telomerase and ALT are used by human cancer cells to lengthen their telomeres with the former being adopted in 85-90% of the cases and the latter in the remaining portion. Because of this, the two mechanisms represent potential targets for anti-cancer therapies. TERRA is the long non-coding RNA transcribed at telomeres by RNA pol II in a variety of organisms. The exact function of the transcript is still unknown but gathering evidence proposes its involvement in several processes, including telomere maintenance. Emerging data validate the importance of TERRA, and the RNA-DNA hybrids it forms at telomeres, especially in ALT. Indeed, the transcript is upregulated in this type of cancer cells and telomeric RNA-DNA hybrids appear to be key triggers of telomeric HDR. Little is known about the source of the lncRNA increased abundance in ALT and how TERRA RNA-DNA hybrids promote telomere lengthening via recombination. Uncovering these hidden aspects might be relevant to further understand the alternative lengthening mechanism of telomeres and develop more efficient therapeutics against cancer. In this study, Saccharomyces cerevisiae post-senescent ALT-survivors, which lengthen their telomeres in a similar manner to human ALT, were employed to address the questions: is TERRA required for ALT and why is it required? In this regard, TERRA levels were measured in survivors to see if they upregulate the transcript like their human counterpart. Following, the regulation of the lncRNA expression was characterized. Interestingly, TERRA abundance resulted to be increased in survivors in a manner that resembled human ALT. The main source of this upregulation seemed to be impaired degradation. Moreover, TERRA expression was regulated in a cell cycle- and telomere length-dependent manner, with the transcript peaking in early S-phase and at short telomeres, respectively. The increase of the lncRNA at short telomeres is believed to trigger HDR and telomere elongation. In pre-survivor cells, telomere erosion triggers senescence, whose rate is negatively influenced by the abundance of TERRA RNA-DNA hybrids. Since survivors likewise shorten their telomeres, they were monitored for the presence of a senescence-like phenotype and how telomeric hybrids might affect it. Surprisingly, ALT-survivors senesced in response to telomere shortening and the pace was negatively regulated by the amount of TERRA RNA-DNA hybrids. This phenomenon is named hereafter “post-crisis senescence”. Overall, this study shows that TERRA might be relevant in ALT to promote lengthening via HDR and avert senescence. The data here presented are expected to broaden the current knowledge of telomere transcription in ALT and emphasize its relevance as target for therapeutic applications.
DDC: 000 Allgemeines
000 Generalities
500 Naturwissenschaften
500 Natural sciences and mathematics
570 Biowissenschaften
570 Life sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 10 Biologie
Place: Mainz
URN: urn:nbn:de:hebis:77-openscience-928433da-bd91-4836-bfc7-952ab645a7a30
Version: Original work
Publication type: Dissertation
License: In Copyright
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Extent: viii, 120 Seiten
Appears in collections:JGU-Publikationen

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