Liquid-liquid phase separation of lamin drives altered chromatin organization in cardiomyopathic mutations of lamin A.

Lamins are intermediate filaments constituting the nuclear lamina which maintains the structural integrity of the nucleus and play a key role in the spatiotemporal genome organization. Mutations in lamin A/C have been associated with a plethora of diseases including dilated cardiomyopathy. In this study, we focused on lamin A mutants E161K and K97E which are widely reported in patients afflicted with dilated cardiomyopathy. We established that these mutations cause large scale disruption of the peripheral lamina and consequent heterochromatin (HC) organization, along with the formation of lamin A aggregates inside the nucleoplasm. Using coarse-grained polymer simulations, we explored the interplay between lamin, nuclear membrane, and chromatin showing that disruptions in these interactions can reproduce the experimental phenotypes. Simulations also predict altered positioning depending on HC content and altered lamin dynamics in E161K and K97E mutants. The predictions from the simulations were verified using 3D FISH to delineate the reorganization of chromosome territories in these mutants. Based on the disengagement of lamin A foci from HC, we subsequently investigated the dynamic properties of the mutant aggregates using advanced imaging techniques. Through this, we report that mutant lamin aggregates show internal rearrangement and external exchange at the mesoscopic-level reminiscent of liquid-liquid phase separation.