Lamins (A/C and B) are major constituents of the nuclear lamina (NL). Structurally conserved lamina-associated domains (LADs) are formed by genomic regions that contact the NL. Lamins are also found in the nucleoplasm, with a yet unknown function. Here we map the genome-wide localization of lamin B1 in an euchromatin-enriched fraction of the mouse genome and follow its dynamics during the epithelial-to-mesenchymal transition (EMT). Lamin B1 associates with actively expressed and open euchromatin regions, forming dynamic euchromatin lamin B1-associated domains (eLADs) of about 0.3 Mb. Hi-C data link eLADs to the 3D organization of the mouse genome during EMT and correlate lamin B1 enrichment at topologically associating domain (TAD) borders with increased border strength. Having reduced levels of lamin B1 alters the EMT transcriptional signature and compromises the acquisition of mesenchymal traits. Thus, during EMT, the process of genome reorganization in mouse involves dynamic changes in eLADs

This work was supported by grants from the Instituto de Salud Carlos III (ISCIII) FIS/FEDER (PI15/00396; CPII14/0006), Ministerio de Economía y Competitividad (MINECO) (SAF2013-40922-R1; FPU14/0407; BFU2016-75008-P), Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional-FEDER (SAF2016-76461-R), Generalitat de Catalunya (2014 SGR 32), Fundació FERO, Fundació La Marató TV3, and La Caixa Foundation. We also thank the Advanced Light Microscopy Unit at the CRG for their assistance and the Cellex Foundation for providing research facilities and equipment. M.A.M.-R. acknowledges funding from the European Research Council under the 7th Framework Program (FP7/2010-2015, ERC grant agreement 609989), the European Union’s Horizon 2020 research and innovation program (agreement 676556), the Spanish Ministry of Economy and Competitiveness (BFU2013-47736-P), and the Centro de Excelencia Severo Ochoa 2013-2017 (SEV-2012-0208) to the CRG