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Differential features of lamina-associated domains mapped by ChIP-sequencing from sonicated or micrococcal nuclease-digested chromatin

ABSTRACT: The nuclear lamina interacts with the genome through megabase-size lamina-associated domains (LADs). LADs have been identified in proximity labeling assays and recently by chromatin immunoprecipitation-sequencing (ChIP-seq) of A- and B-type lamins. LADs localize mainly to the nuclear periphery, they are gene-poor and largely heterochromatic. Here, we show that the mode of chromatin fragmentation for ChIP, namely either bath sonication (used to date for ChIP of nuclear lamins) or digestion with micrococcal nuclease (MNase) leads to the discovery of distinct sets of lamin-interacting domains (which we refer to as LiDs) with distinct gene content, histone composition enrichment and relationship to lamin B1-interacting domains. We find that total genome coverage by lamin A/C ('LMNA') LiDs identified in sonicated or MNase-digested chromatin is similar (~730 megabases). Over half of these domains, however, are uniquely detected in sonicated or MNase-digested chromatin. Whereas sonication-specific LMNA LiDs are gene-poor and devoid of a broad panel of histone modifications, MNase-specific LMNA LiDs are of higher gene density and are enriched in H3K9me3, H3K27me3 and in histone variant H2A.Z. Analysis of published LMNB1 LADs and of LMNB1 LiDs identified by ChIP-seq further shows that LMNA can associate with 'open' chromatin domains displaying euchromatin features which are not associated with LMNB1. The differential genetic and epigenetic properties of lamin-interacting chromatin domains indicate the existence of distinct LiD populations identifiable in different chromatin contexts, including nuclease-accessible 'open' regions presumably localized in the nuclear interior.

ORGANISM(S): Homo sapiens

PROVIDER: GSE57149 | GEO | 2015/03/24

SECONDARY ACCESSION(S): PRJNA245783

REPOSITORIES: GEO

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Project description:Purpose: to qualify and quantify the rearrangement of interactions of nuclear lamins A/C and B with the genome, in relation to nuclearradial repositioning of loci and changes in gene expression, in HepG2 cells exposed to cyclosporin A. .To compare HepG2 cell line transcriptome profiling (RNA-seq) with radially positioning of the chromatin anchored at the nuclear periphery before and after CsA treatment. Methods: To this end, we mapped lamin A and lamin B lamina-associated domains (LADs) by chromatin immunoprecipitation-sequencing (ChIP-seq) of lamin A/C (antibody sc7292x, Santa Cruz Biotechnology) and lamin B1 (antibody ab16048, Abcam), respectively. HepG2 cells were either cultured under proliferative conditions (controls) or exposed for 3 days to 10 uM cyclosporin A. We also assesed the transcriptome by RNA-seq under each condition in duplicate cultures. Results: CsA elicits accumulation of pre-lamin A in HepG2 cells, raising the hypothesis of a global rearrangement of lamin-chromatin interactions. We show here the existence of overlapping and distinct lamin A and B lamina-associated domains (which we refer to as A- and B-LADs, respectively). Whereas B-LADs largely remain constitutive, CsA elicits the formation of facultative A-LADs. Re-localization of A-LADs occur mainly on preexisting B-LADs. However, LAD rearrangement does not correlate with systematic changes in gene expression within LADs. We find a reorganization of A- and B-LADs after CsA treatment, entailing distinct contributions of A- and B- type lamins. to genome organization. Indeed, classification of lamin A LADs and lamin B LADs into properties of ‘A-only’, ‘B-only’ and ‘A-B’ LADs show an overall loss of A-only LADs after CsA treatment. A- only and B-only LADs are highly dynamic with A-B LADs being more stable.The rearrangement of lamin association after CsA treatment correlates with repositioning of loci in the nuclear space with, notably, a loss of lamin B associated with a re-localization of loci towards the nuclear center and conversely, a gain of lamin B linked to a repositioning of loci towards the nuclear periphery. Predictions on radial repositioning of LADs, and of loci within, from 3D structural models of the genome were supported by fluorescence in situ hybridization (FISH) analyses. Conclusions: We show that, while they amply co-localize on well-conserved LADs, lamins A and B also interact with distinct genomic regions that can interchange (switch) between lamin A and B upon CsA treatment. We unveil distinct lamin A and B interactions with chromatin, suggesting complementary contributions to genome conformation. Our data suggest that and lamins A and B may differentially modulate genome organization.

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Differential features of lamina-associated domains mapped by ChIP-sequencing from sonicated or micrococcal nuclease-digested chromatin

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