Abstract
Chromatin organization within the nuclear volume is essential to regulate many aspects of its function and to safeguard its integrity. A key player in this spatial scattering of chromosomes is the nuclear envelope (NE). The NE tethers large chromatin domains through interaction with the nuclear lamina and other associated proteins. This organization is perturbed in cells from Hutchinson–Gilford progeria syndrome (HGPS), a genetic disorder characterized by premature aging features. Here, we show that HGPS-related lamina defects trigger an altered 3D telomere organization with increased contact sites between telomeres and the nuclear lamina, and an altered telomeric chromatin state. The genome-wide replication timing signature of these cells is perturbed, with a shift to earlier replication for regions that normally replicate late. As a consequence, we detected a higher density of replication forks traveling simultaneously on DNA fibers, which relies on limiting cellular dNTP pools to support processive DNA synthesis. Remarkably, increasing dNTP levels in HGPS cells rescued fragile telomeres, and improved the replicative capacity of the cells. Our work highlights a functional connection between NE dysfunction and telomere homeostasis in the context of premature aging.
Highlights
Telomeres are specialized nucleoprotein complexes capping the ends of linear chromosomes
We did not detect any differences in fold enrichment with or without m6A methylation, confirming that qPCR is a suitable approach to assess the amount of purified telomeres in Human Dermal Fibroblasts (HDF) samples, regardless of their methylation status (Fig. 1F-left panel)
Analysis of the resulting blots revealed that M.EcoGII-LaminB1 was able to methylate genomic DNA in NLS-EGFP, EGFP-LA and EGFP-tagged human LaminA∆50/progerin (EGFP-PG) cells (Fig. 1G, see Input samples). m6A signal was detectable on isolated telomeres for all three samples, which indicates that a subset of telomeres contact the nuclear lamina in asynchronous HDF c ells[35]
Summary
Telomeres are specialized nucleoprotein complexes capping the ends of linear chromosomes. Premature aging disorders are usually caused by mutations impairing the DNA damage response and repair pathways (Ataxia Telangiectasia), shelterin complex structure (Dyskeratosis Congenita), and telomere length regulation (Dyskeratosis Congenita, Bloom and Werner Syndromes). These telomere-related syndromes share overlapping traits with human syndromes linked to lamins, grouped under the term of laminopathies[10]. Right panel: isolated telomeres from HDF expressing NLS-EGFP, EGFP-LA, or EGFP-PG as indicated. The nuclear architecture defects observed in progerin-expressing cells have dramatic consequences on chromatin organization, with a loss of some heterochromatin-lamina domains, decreased interactions within heterochromatin domains, and epigenetic alterations in L ADs26–28. Connection between telomeres and lamins occurs in the nucleoplasm and plays a role in telomere protection[36]
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