Nuclear βactin dependent chromatin accessibility governs stem cell pluripotency and extracellular matrix gene programs to maintain cellular biomechanics for cell lineage decisions

Abstract

Pluripotency requires coordinated regulation of chromatin state, transcription and extracellular matrix (ECM) mechanics, but how these layers are integrated remains unclear. Here, using {beta}-actin knockout mouse embryonic stem cells (mESCs) and a nuclear-targeted {beta}-actin rescue, we identify nuclear {beta}-actin as a key regulator linking chromatin accessibility to mechanosensitive control of cell fate. {beta}-actin loss reduced OCT4, SOX2 and NANOG, broadly rewired the transcriptome and proteome and decreased accessibility at pluripotency regulatory regions. Integrated RNA-seq and ATAC-seq revealed coordinated dysregulation of stemness, ECM, mechanotransduction and early-lineage programs. These changes were accompanied by fibronectin and collagen upregulation, altered nuclear morphology, reduced Lamin A/C and mechanosensing proteins, increased nuclear YAP1 and greater ECM stiffness heterogeneity. Functionally, knockout cells displayed biased lineage specification, failed neuronal differentiation, ectopic cardiomyocyte-like differentiation, and markedly reduced teratoma growth with diminished ectodermal representation. Nuclear {beta}-actin re-expression restored many molecular, mechanical and differentiation defects, although chromatin rescue remained incomplete. Together, these findings establish nuclear {beta}-actin as an integrator of chromatin regulation and ECM-dependent mechanotransduction that preserves pluripotency and developmental competence.