Human Telomeres Are Tethered to the Nuclear Envelope during Postmitotic Nuclear Assembly

Telomeres are essential for nuclear organization in yeast and during meiosis in mice. Exploring telomere dynamics in living human cells by advanced time-lapse confocal microscopy allowed us to evaluate the spatial distribution of telomeres within the nuclear volume. We discovered an unambiguous enrichment of telomeres at the nuclear periphery during postmitotic nuclear assembly, whereas telomeres were localized more internally during the rest of the cell cycle. Telomere enrichment at the nuclear rim was mediated by physical tethering of telomeres to the nuclear envelope, most likely via specific interactions between the shelterin subunit RAP1 and the nuclear envelope protein Sun1. Genetic interference revealed a critical role in cell-cycle progression for Sun1 but no effect on telomere positioning for RAP1. Our results shed light on the dynamic relocalization of human telomeres during the cell cycle and suggest redundant pathways for tethering telomeres to the nuclear envelope.