scholarly journals An Emerin LEM-Domain Mutation Impairs Cell Response to Mechanical Stress

Cells ◽  
2019 ◽  
Vol 8 (6) ◽  
pp. 570 ◽  
Author(s):  
Nada Essawy ◽  
Camille Samson ◽  
Ambre Petitalot ◽  
Sophie Moog ◽  
Anne Bigot ◽  
...  

Emerin is a nuclear envelope protein that contributes to genome organization and cell mechanics. Through its N-terminal LAP2-emerin-MAN1 (LEM)-domain, emerin interacts with the DNA-binding protein barrier-to-autointegration (BAF). Emerin also binds to members of the linker of the nucleoskeleton and cytoskeleton (LINC) complex. Mutations in the gene encoding emerin are responsible for the majority of cases of X-linked Emery-Dreifuss muscular dystrophy (X-EDMD). Most of these mutations lead to an absence of emerin. A few missense and short deletion mutations in the disordered region of emerin are also associated with X-EDMD. More recently, missense and short deletion mutations P22L, ∆K37 and T43I were discovered in emerin LEM-domain, associated with isolated atrial cardiac defects (ACD). Here we reveal which defects, at both the molecular and cellular levels, are elicited by these LEM-domain mutations. Whereas ΔK37 mutation impaired the correct folding of the LEM-domain, P22L and T43I had no impact on the 3D structure of emerin. Surprisingly, all three mutants bound to BAF, albeit with a weaker affinity in the case of ΔK37. In human myofibroblasts derived from a patient’s fibroblasts, emerin ∆K37 was correctly localized at the inner nuclear membrane, but was present at a significantly lower level, indicating that this mutant is abnormally degraded. Moreover, SUN2 was reduced, and these cells were defective in producing actin stress fibers when grown on a stiff substrate and after cyclic stretches. Altogether, our data suggest that the main effect of mutation ΔK37 is to perturb emerin function within the LINC complex in response to mechanical stress.

2010 ◽  
Vol 21 (2) ◽  
pp. 254-265 ◽  
Author(s):  
Osamu Iwasaki ◽  
Atsunari Tanaka ◽  
Hideki Tanizawa ◽  
Shiv I.S. Grewal ◽  
Ken-ichi Noma

The eukaryotic genome is a complex three-dimensional entity residing in the nucleus. We present evidence that Pol III–transcribed genes such as tRNA and 5S rRNA genes can localize to centromeres and contribute to a global genome organization. Furthermore, we find that ectopic insertion of Pol III genes into a non-Pol III gene locus results in the centromeric localization of the locus. We show that the centromeric localization of Pol III genes is mediated by condensin, which interacts with the Pol III transcription machinery, and that transcription levels of the Pol III genes are negatively correlated with the centromeric localization of Pol III genes. This centromeric localization of Pol III genes initially observed in interphase becomes prominent during mitosis, when chromosomes are condensed. Remarkably, defective mitotic chromosome condensation by a condensin mutation, cut3-477, which reduces the centromeric localization of Pol III genes, is suppressed by a mutation in the sfc3 gene encoding the Pol III transcription factor TFIIIC subunit, sfc3-1. The sfc3-1 mutation promotes the centromeric localization of Pol III genes. Our study suggests there are functional links between the process of the centromeric localization of dispersed Pol III genes, their transcription, and the assembly of condensed mitotic chromosomes.


2020 ◽  
Vol 127 (Suppl_1) ◽  
Author(s):  
Yuan Zhang ◽  
Mohamed Ameen ◽  
Isaac Perea Gil ◽  
Jennifer Arthur ◽  
Alexandra A Gavidia ◽  
...  

Background: LMNA , a gene encoding A-type lamin proteins (abbreviated as lamin A), is one of the most frequently mutated genes in dilated cardiomyopathy (DCM). The molecular mechanisms underlying cardiomyocyte dysfunction in LMNA -related DCM remain elusive, translating to the lack of disease-specific therapies. Lamin A has been shown to play a critical role in genome organization via interactions with the chromatin at specific regions called lamina-associated domains (LADs). However, little is known about whether DCM-causing LMNA mutations rearrange the genome conformation and chromosome accessibility. The overarching goal of this study is to define the role of genome organization in LMNA -related DCM. Methods: LMNA -related DCM was modeled in vitro using cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) from DCM patients carrying a frameshift mutation in the LMNA gene (c. 348_349insG; p. K117fs) and isogenic controls. We combined genome-wide single cell functional genomic and epigenomic mapping analyses to define the gene regulation and cis-regulatory interactions in isogenic iPSC-CMs. Results: Single-cell RNA-seq revealed global gene dysregulation in LMNA mutant compared to isogenic control iPSC-CMs. The homeodomain transcription factor PRRX1 was significantly upregulated in mutant cells. We showed that LAD integrity is disrupted at the PRRX1 locus in mutant iPSC-CMs. In agreement, DNA fluorescence in situ hybridization (FISH) revealed that the PRRX1 locus loses peripheral association and relocates towards the transcriptionally active nuclear interior in mutant iPSC-CMs. Correspondingly, single-cell assay for transposase accessible chromatin (ATAC)-seq showed increased chromatin co-accessibility at the PRRX1 locus, providing a plausible explanation for ectopic activation of PRRX1 in LMNA mutant iPSC-CMs. Conclusion: Our data suggest that LMNA haploinsufficiency disrupts the structure of LADs, leading to ectopic promoter interactions and altered gene expression in LMNA -related DCM iPSC-CMs. We identified PRRX1 as a promising candidate locus linking changes in LAD organization with gene dysregulation in LMNA -related DCM.


2020 ◽  
Vol 126 (3) ◽  
Author(s):  
Julie Heffler ◽  
Parisha P. Shah ◽  
Patrick Robison ◽  
Sai Phyo ◽  
Kimberly Veliz ◽  
...  

Rationale: Mechanical forces are transduced to nuclear responses via the linkers of the nucleoskeleton and cytoskeleton (LINC) complex, which couples the cytoskeleton to the nuclear lamina and associated chromatin. While disruption of the LINC complex can cause cardiomyopathy, the relevant interactions that bridge the nucleoskeleton to cytoskeleton are poorly understood in the cardiomyocyte, where cytoskeletal organization is unique. Furthermore, while microtubules and desmin intermediate filaments associate closely with cardiomyocyte nuclei, the importance of these interactions is unknown. Objective: Here, we sought to determine how cytoskeletal interactions with the LINC complex regulate nuclear homeostasis in the cardiomyocyte. Methods and Results: To this end, we acutely disrupted the LINC complex, microtubules, actin, and intermediate filaments and assessed the consequences on nuclear morphology and genome organization in rat ventricular cardiomyocytes via a combination of super-resolution imaging, biophysical, and genomic approaches. We find that a balance of dynamic microtubules and desmin intermediate filaments is required to maintain nuclear shape and the fidelity of the nuclear envelope and lamina. Upon depletion of desmin (or nesprin [nuclear envelope spectrin repeat protein]-3, its binding partner in the LINC complex), polymerizing microtubules collapse the nucleus and drive infolding of the nuclear membrane. This results in DNA damage, a loss of genome organization, and broad transcriptional changes. The collapse in nuclear integrity is concomitant with compromised contractile function and may contribute to the pathophysiological changes observed in desmin-related myopathies. Conclusions: Disrupting the tethering of desmin to the nucleus results in a loss of nuclear homeostasis and rapid alterations to cardiomyocyte function. Our data suggest that a balance of forces imposed by intermediate filaments and microtubules is required to maintain nuclear structure and genome organization in the cardiomyocyte.


1991 ◽  
Vol 230 (1-2) ◽  
pp. 332-336 ◽  
Author(s):  
Hisami Yamada ◽  
Takayuki Yoshida ◽  
Ken-ichi Tanaka ◽  
Chihiro Sasakawa ◽  
Takeshi Mizuno

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