Emerin modulates spatial organization of chromosome territories in cells on softer matrices

Abstract

Cells perceive and relay external mechanical forces into the nucleus through the nuclear envelope. Here we examined the effect of lowering substrate stiffness as a paradigm to address the impact of altered mechanical forces on nuclear structure-function relationships. RNA sequencing of cells on softer matrices revealed significant transcriptional imbalances, predominantly in chromatin associated processes and transcriptional deregulation of human Chromosome 1. Furthermore, 3-Dimensional fluorescence in situ hybridization (3D-FISH) analyses showed a significant mislocalization of Chromosome 1 and 19 Territories (CT) into the nuclear interior, consistent with their transcriptional deregulation. However, CT18 with relatively lower transcriptional dysregulation, also mislocalized into the nuclear interior. Furthermore, nuclear Lamins that regulate chromosome positioning, were mislocalized into the nuclear interior in response to lowered matrix stiffness. Notably, Lamin B2 overexpression retained CT18 near the nuclear periphery in cells on softer matrices. While, cells on softer matrices also activated emerin phosphorylation at a novel Tyr99 residue, the inhibition of which in a phospho-deficient mutant (emerinY99F), selectively retained chromosome 18 and 19 but not chromosome 1 territories at their conserved nuclear locations. Taken together, emerin functions as a key mechanosensor, that modulates the spatial organization of chromosome territories in the interphase nucleus.

Chromatin dynamics governed by a set of nuclear structural proteins

“…Depletion of nuclear structural proteins, such as lamin A/C, may explain two major hallmarks of cancer: aberrations in nuclear morphology and aneuploidy . It also affects another hallmark of cancer cells, which is chromosome aberrations . Mutations or loss of nuclear structural proteins and other cellular factors also affect the positioning of diverse human genes, the regulation of cell process, chromatin loop domains, and chromosome dynamics, which we discuss here.…”

“…25,26 It also affects another hallmark of cancer cells, which is chromosome aberrations. [27][28][29] Mutations or loss of nuclear structural proteins and other cellular factors also affect the positioning of diverse human genes, 30 the regulation of cell process, 31,32 chromatin loop domains, 33,34 and chromosome dynamics, 35 which we discuss here.…”

Structure-Function Relationships of Nuclear Lamins

“…This was consistent with enrichment in nucleoplasmic lamin levels in cells cultured on softer matrices. Remarkably, lamins were restored to the nuclear envelope in cells transferred from softer to stiffer substrates [145]. Taken together, lamins respond to external mechanical signals in a phosphorylation-dependent mechanism.…”

Nuclear Functions of the Tyrosine Kinase Src

“…Guilluy and colleagues showed that the phosphorylation of Y74 and Y95 of emerin residues by Src mediates the mechanical adaptation of nuclei to mechanical force [71]. Some recent evidence demonstrate that the cells cultured on soft matrices induced emerin phosphorylation and the mislocalization of nuclear envelope proteins in the nucleoplasm [72]. The authors also suggest that emerin is able to reorganize the chromosome territories in cells on softer matrix and they speculate that emerin phosphorylation acts as an upstream regulator of lamin localization resulting in substantial changes of the transcriptional regulation in a substrate stiffness-dependent manner [72].…”