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Telomere resolution and genomic instability in mouse embryonic stem cells Lisaingo, Kathleen

Abstract

Proper segregation of replicated chromosomes is essential for cell division in all organisms. Linear eukaryotic chromosomes contain specialized protective structures at the chromosome ends, called telomeres, which are essential for maintaining genome stability. Telomere associations have been observed during key cellular processes including mitosis, meiosis and carcinogenesis. These telomere associations need to be resolved prior to cell division to avoid loss of telomere function. TRF1, a core component of the telomere protein complex shelterin, has been implicated as a mediator of telomere associations. To determine the effect of TRF1 protein levels on telomere associations, we used live-cell fluorescence microscopy to visualize telomeres and chromosome dynamics in cells expressing defined levels of TRF1. Elevated levels of TRF1 induced anaphase bridges containing thin “thread-like” stretches of TRF1 foci connecting segregating chromosomes. We also observed telomere aggregates, mitotic bypass, and TRF1 bridges persisting into the following cell cycle. To examine the role of TRF1 in these telomere associations, we generated a TRF1 protein which can be inducibly cleaved by TEV protease. Telomere aggregates appeared to resolve upon cleavage of TRF1 proteins, suggesting that telomere associations result primarily from protein interactions mediated by TRF1. The essential helicase RTEL1 was observed at the extremities of persistent TRF1 bridges, possibly indicating a function for RTEL1 in the resolution of TRF1-induced telomere associations. Taken together, our results demonstrate that precise regulation of TRF1 levels is essential for telomere resolution and mitotic segregation.

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