Student Theses and Dissertations

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

de Lange Laboratory


Telomeres are the key structures that protect the ends of linear chromosomes. Although they are often thought about in the context of cellular aging, their most important role is actually to protect the end of the DNA from being mis-interpreted as a site of DNA damage. Telomeres are thought to accomplish this through the action of shelterin. Shelterin is a multi-protein complex where each subunit is dedicated to a specific role in repressing a form of DNA damage signaling, repair, or recruiting telomerase to extend the telomere end. One of the critical anchor points of shelterin is a protein known as TRF2. TRF2 is necessary to protect telomeres from becoming fused by non-homologous end-joining, and from one of the two main DNA damage signaling pathways, in this case the one driven by ATM and CHK2. It is thought to do this by rearranging the very 3’ end of the DNA into a duplex loop – known as the t-loop. Together, TRF2 and t-loops are the main pillars of the t-loop model of end-protection, which is the focus of this thesis. The first part of this thesis presents an overview of telomere protection and focuses specifically on what is known about end-protection in mammalian cells. From there, we test an alternative model of telomere end-protection, and find it to be unsubstantiated. We next analyze how TRF2 contributes to t-loop formation, including whether TRF2 cooperates with other shelterin components, uses non-shelterin factors, and which domains of TRF2 contribute. Finally, we try to understand how t-loops are made, and whether there are any external factors that assist TRF2, or whether TRF2 is self-sufficient in repressing signaling, fusions, and forming t-loops. We then discuss the evolution of telomeres which serves as an important reference point towards understanding the greater context of the t-loop model, and its plausibility. The appendix discusses attempts to push the resolution of t-loop imaging in the context of whole cells. The work presented here is of relevance to understanding the central mechanism of telomere end protection. What t-loops do – if anything – and how they are made is a question that is at the heart of telomere biology.


A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

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