DNA damage responses to loss of telomere integrity

Thesis

Linear genomes end in characteristic structures consisting of repetitive DNA and proteins: the telomeres. These play two critical roles: on one hand they avoid the of loss of genetic information due to the incomplete replication of the chromosome ends and on the other, they provide capping structures for chromosome termini, differentiating them from double strand breaks. Telomeres contain specialized proteins (the shelterin complex), as well as proteins present elsewhere on the chromosomes (chromatin remodelling, DNA damage repair and response factors). Interestingly, several DNA damage factors are required for proper telomere maintenance, drawing a thin line between telomere protection and their recognition as broken DNA ends.

Loss of telomere integrity has severe consequences for the cell, namely it can induce replicative senescence and cellular aging, or it can contribute to tumorigenesis. How telomeres are capped and how they are perceived by the cell when they become dysfunctional is essential for our understanding of the contribution of loss of telomere integrity to aging and disease. In order to unravel new factors involved in telomere maintenance, siRNA screens were performed. The optimization process has confirmed both telomeric foci and telomere dysfunction-induced foci (TIFs) as suitable readouts and the screens performed generated a list of potential candidate genes involved in telomere biology. Although some of the candidate genes tested in this work failed the validation process, other genes deserve further analysis.

In addition this work also studied the role of several DNA damage factors at uncapped telomeres. Furthermore, BRCA1, CtIP and EXO1 were found to be critical for the formation of end-to-end fusions generated after TRF2 inactivation. The requirement of this proteins in this process, suggests that not only that not only the classical non-homologous end joining (C-NHEJ) pathway is active at TRF2-depelted telomeres, but emphasises the multiplicity of mechanisms that act to repair dysfunctional telomeres.

Authors: Carlos, AR

• Publication date: 2013
• DOI: 10.5287/ora-n1dgjwpnq
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: BRCA1; EXO1; CtIP; Telomere integrity; DNA damage response
• Subjects: DNA damage signalling; Biology (medical sciences)