A Balance Between Intermediate Filaments and Microtubules Maintains Nuclear Architecture in the Cardiomyocyte
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ABSTRACT:
ORGANISM(S): Rattus norvegicus
PROVIDER: GSE144147 | GEO | 2020/01/24
REPOSITORIES: GEO
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Project description: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.
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Project description:A Balance Between Intermediate Filaments and Microtubules Maintains Nuclear Architecture in the Cardiomyocyte
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Project description:Although best known as core components of RNA silencing pathways in the cytoplasm, Argonautes have been shown to regulate gene expression by functioning in the nucleus. Previous work showed that Drosophila AGO2 is preferentially associated with active promoters and can activate gene expression by promoting looping to an enhancer. In order to elucidate the genome-wide role of AGO2 in regulating transcription, we performed mass spec analysis of factors that interact with AGO2 in nuclear extracts and found RNA Pol II and LaminB among the top-associated proteins. Using nascent RNA sequencing, we showed that AGO2 and LaminB co-repress transcription at borders between both LaminB-associated domains (LAD) and topologically-associated domains (TADs). Furthermore, LaminB and AGO2 specifically prevent RNA Pol II recruitment at repressed genes, and AGO2 additionally impairs the ability of RNA Pol II to extend into active elongation. Using mRNA-seq profiling, we identified a somatic target of AGO2 repression, nht, which leads to ectopic expression of spermatogenesis genes in AGO2 null mutants. Interestingly, nht is immersed in a LAD located within a repressive TAD flanked by AGO2 binding sites. 4C-seq analysis showed that depletion of either AGO2 or LaminB results in a significant decrease in frequency of interactions within the TAD as well as ectopic inter-TAD interactions. Overall, our findings reveal a coordinated function for AGO2 and LaminB in dictating the overall architecture of the genome to control the recruitment of RNA Pol II and thereby regulate gene expression.
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Project description:Drosophila Argonaute2 (AGO2) is known to regulate expression of certain loci in an RNA interference-independent manner, but its genome-wide function on chromatin remains unknown. In order to elucidate the mechanism by which AGO2 regulates transcription, we performed mass spec analysis of factors that interact with AGO2 in nuclear extracts and identified RNA Polymerase II (Pol II) and LaminB among the top-associated proteins. We found that AGO2 and LaminB attenuate transcription genome-wide, including borders between both LaminB-associated domains (LADs) and topologically-associated domains (TADs). Furthermore, we identified a somatic target of AGO2 transcriptional repression, nht, which is immersed in a LAD located within a repressive TAD. Null mutation of AGO2 leads to ectopic expression of spermatogenesis genes dependent on nht. Finally, depletion of either AGO2 or LaminB results in reduced looping interactions within the TAD as well as ectopic inter-TAD interactions, as detected by 4C-seq analysis. Overall, our findings reveal coordination of AGO2 and LaminB to dictate overall genome architecture and thereby regulate gene expression.
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