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The molecular basis of lamin- chromatin interactions [SAMMY-Seq]

ABSTRACT: Lamins are the main constituents of the nuclear lamina, a fibrillar layer underlying the inner nuclear membrane. The nuclear lamina governs chromatinorganization through lamina-associated domainswithin the densely packed heterochromatin regions. Employing cryo-focused ion beam (cryo-FIB) milling in conjunction withcryo-electron tomography (cryo-ET), we mappedthe concentration of nucleosomesat the lamin-chromatin interface. Depletion of lamin A/C induces nanometer-scale chromatin decompaction, macroscopic-scale alterations in gene expression and chromatin-wide alterations of chromatin properties, revealed by 4f-genome-wide analysis. Cryo-electron microscopy (cryo-EM) structural analysis revealed a specific interaction between nucleosomes and the tail domain of lamin A. A unique motif of lamin A that distinguishes it from other lamin isoforms. These findings illuminatethe dynamic interplay between specific lamins and chromatin, shaping chromatin architecture and epigenetic regulation.

ORGANISM(S): Mus musculus

PROVIDER: GSE268924 | GEO | 2025/05/28

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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The molecular basis of lamin- chromatin interactions [SAMMY-Seq]

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