title: The DDR at telomeres lacking intact shelterin does not require substantial chromatin decompaction.
abstract: Telomeres are protected by shelterin, a six-subunit protein complex that represses the DNA damage response (DDR) at chromosome ends. Extensive data suggest that TRF2 in shelterin remodels telomeres into the t-loop structure, thereby hiding telomere ends from double-stranded break repair and ATM signaling, whereas POT1 represses ATR signaling by excluding RPA. An alternative protection mechanism was suggested recently by which shelterin subunits TRF1, TRF2, and TIN2 mediate telomeric chromatin compaction, which was proposed to minimize access of DDR factors. We performed superresolution imaging of telomeres in mouse cells after conditional deletion of TRF1, TRF2, or both, the latter of which results in the complete loss of shelterin. Upon removal of TRF1 or TRF2, we observed only minor changes in the telomere volume in most of our experiments. Upon codeletion of TRF1 and TRF2, the telomere volume increased by varying amounts, but even those samples exhibiting small changes in telomere volume showed DDR at nearly all telomeres. Upon shelterin removal, telomeres underwent 53BP1-dependent clustering, potentially explaining at least in part the apparent increase in telomere volume. Furthermore, chromatin accessibility, as determined by ATAC-seq (assay for transposase-accessible chromatin [ATAC] with high-throughput sequencing), was not substantially altered by shelterin removal. These results suggest that the DDR induced by shelterin removal does not require substantial telomere decompaction.
authors.affiliation: Laboratory for Cell Biology and Genetics, Rockefeller University, New York, New York 10021, USA.
authors.forename: Leonid A
authors.initials: LA
authors.lastname: Timashev
authors.affiliation: Center for Advanced Imaging, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Hazen
authors.initials: H
authors.lastname: Babcock
authors.affiliation: Center for Advanced Imaging, Harvard University, Cambridge, Massachusetts 02138, USA.|Howard Hughes Medical Institute, Harvard University, Cambridge, Massachusetts 02138, USA.|Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.|Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Zhuang
authors.affiliation: Laboratory for Cell Biology and Genetics, Rockefeller University, New York, New York 10021, USA.
authors.forename: Titia
authors.initials: T
authors.lastname: de Lange
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002843:Chromatin / Q000502:physiology; D004249:DNA Damage; D051379:Mice; D008856:Microscopy, Fluorescence; D016615:Telomere / Q000648:ultrastructure*; D035321:Telomeric Repeat Binding Protein 1 / Q000502:physiology*; D035341:Telomeric Repeat Binding Protein 2 / Q000502:physiology*; D000071857:Tumor Suppressor p53-Binding Protein 1 / Q000502:physiology
chemical_list: D002843:Chromatin; C534796:TRF2 protein, mouse; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; C498302:Trp53bp1 protein, mouse; D000071857:Tumor Suppressor p53-Binding Protein 1
keywords: DNA damage response; STORM imaging; chromatin; shelterin; t loop; telomere