Cardiomyopathic mutations of lamin A perturb mutual interactions of lamin, nuclear membrane, and chromatin leading to LLPS

Lamins are nuclear intermediate filaments constituting the nuclear lamina which maintains the structural integrity of the nucleus and play a key role in the spatial organisation of the genome. Mutations in the lamin protein have been associated with diverse diseases collectively known as laminopathies. In this study, we focused on two lamin A mutants - E161K and K97E - associated with dilated cardiomyopathy (DCM). Through confocal imaging, we established that these mutations cause large scale disruption of the peripheral lamin and consequent heterochromatin organisation, along with the formation of lamin aggregates inside the nucleoplasm. Using coarse-grained polymer simulations, we uncovered the role of lamin-lamin, lamin-membrane and lamin-chromatin interactions in maintaining wild-type lamin and chromatin organisation and showed that disruptions in these interactions can reproduce the experimental observations in the lamin mutants. These predictions were verified using 3D-FISH experiments to quantify the reorganisation of chromosome territories in these mutants. Using advanced imaging methods, we characterised the dynamical properties of the lamin aggregates in the mutants to show for the first time a liquid-like state of the lamin aggregates through a liquid-liquid phase separation. The altered lamin and chromatin interactions in the mutants thus manifest as liquid-like aggregates in the nucleoplasm leading to disruption of the spatial organisation of the genome in these laminopathy-associated mutants.