Ruis, Phil;
(2020)
Closing the loop - tales from the end of the chromosome.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Mammalian telomeres protect chromosome ends from aberrant DNA repair. TRF2, a component of the telomere-specific shelterin protein complex, facilitates end protection through sequestration of the terminal telomere repeat sequence within a lariat t-loop structure. Deleting Trf2 in somatic cells abolishes t-loop formation, which coincides with telomere deprotection, chromosome end-to-end fusions, and inviability. In contrast, I establish here that TRF2 is dispensable for telomere protection in mouse pluripotent embryonic and epiblast stem cells. Embryonic stem cell (ESC) telomeres devoid of TRF2 instead activate an attenuated telomeric DNA Damage Response (DDR) without accompanying telomere fusions, and propagate for multiple generations. However, removal of the entire shelterin complex from ESCs induces a striking telomeric DDR, chromosome fusions and a rapid loss of viability, demonstrating the shelterin-dependence of end protection in ESCs. Consistent with TRF2 being dispensable for telomere protection specifically during early embryonic development, cells exiting from pluripotency rapidly switch to TRF2-dependent end protection, and TRF2 null embryos arrest prior to implantation with evidence of strong DDR signaling and apoptosis specifically in the non-pluripotent compartment. I show that ESCs form t-loops independently of TRF2, revealing why TRF2 is dispensable for end protection during pluripotency. I develop approaches to identify how t-loop formation and end protection might be achieved independently of TRF2 in ESCs and document progress using these approaches. Collectively, these data establish that telomere protection is solved by distinct mechanisms in pluripotent and somatic tissues.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Closing the loop - tales from the end of the chromosome |
| Event: | UCL |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| Keywords: | Telomeres, DNA Repair, Chromosome, Pluripotency, Stem cells, Aging, Cancer, Development, End protection, DNA |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10116732 |
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