LAP2alpha maintains a mobile and low assembly state of A-type lamins in the nuclear interior

Lamins form stable filaments at the nuclear periphery in metazoans. Unlike B-type lamins, lamins A and C localize also in the nuclear interior, where they interact with lamin-associated polypeptide 2 alpha (LAP2α). Using antibody labeling, we previously observed a depletion of nucleoplasmic A-type lamins in mouse cells lacking LAP2α. Here, we show that loss of LAP2α actually causes formation of larger, biochemically stable lamin A/C structures in the nuclear interior that are inaccessible to lamin A/C antibodies. While nucleoplasmic lamin A forms from newly expressed pre-lamin A during processing and from soluble mitotic lamins in a LAP2α-independent manner, binding of LAP2α to lamin A/C during interphase inhibits formation of higher order structures, keeping nucleoplasmic lamin A/C in a mobile state independent of lamin A/C S22 phosphorylation. We propose that LAP2α is essential to maintain a mobile lamin A/C pool in the nuclear interior, which is required for proper nuclear functions.

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LAP2alpha maintains a mobile and low assembly state of A-type lamins in the nuclear interior

10.1101/2020.09.25.313296 ◽

2020 ◽

Author(s):

Nana Naetar ◽

Konstantina Georgiou ◽

Christian Knapp ◽

Irena Bronshtein ◽

Elisabeth Zier ◽

...

Keyword(s):

Nuclear Periphery ◽

Higher Order ◽

Lamin A ◽

Independent Manner ◽

Nuclear Interior ◽

Order Structures

AbstractLamins form stable filaments at the nuclear periphery in metazoans. Unlike B-type lamins, lamins A and C localize also in the nuclear interior, where they interact with lamin-associated polypeptide 2 alpha (LAP2α). We show that lamin A in the nuclear interior is formed from newly expressed pre-lamin A during processing and from soluble mitotic mature lamins in a LAP2α-independent manner. Binding of LAP2α to lamins A/C in the nuclear interior during interphase inhibits formation of higher order structures of lamin A/C in vitro and in vivo, keeping lamin A/C in a mobile low assembly state independent of lamin A/C S22 phosphorylation. Loss of LAP2α causes formation of larger, less mobile and biochemically stable lamin A/C structures in the nuclear interior, which reduce the mobility of chromatin. We propose that LAP2α is essential to maintain a mobile lamin A/C pool in the nuclear interior, which is required for proper nuclear functions.

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Expression of nuclear lamins during mouse preimplantation development

Development ◽

10.1242/dev.102.2.271 ◽

1988 ◽

Vol 102 (2) ◽

pp. 271-278

Author(s):

E. Houliston ◽

M.N. Guilly ◽

J.C. Courvalin ◽

B. Maro

Keyword(s):

Cell Differentiation ◽

Early Development ◽

Nuclear Periphery ◽

Preimplantation Development ◽

Lamin A ◽

Positive Staining ◽

Lamin B ◽

Nuclear Lamins ◽

Mouse Cells

The expression of nuclear lamins during mouse preimplantation development was studied by immunofluorescence, immunoblotting and immunoprecipitation. Two sera were used, specific either for lamin B or lamins A and C. Both sera gave a positive staining of the nuclear periphery throughout preimplantation development (fertilized eggs to late blastocysts). Immunoblots revealed that the three lamins were present in eggs and blastocysts. However, lamin A from eggs was found to have a higher apparent Mr than lamin A from blastocysts and other mouse cells. Using immunoprecipitation, synthesis of lamin A was detected in eggs while synthesis of lamin B was detected in 8-cell embryos and blastocysts, indicating that at least some of the lamins used during early development do not come from a store in the egg. These results are discussed in relation to the possible role of lamins during cell differentiation.

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Abstract 508: Nuclear Lamins At Enhancers: A New Hypothesis for Laminopathies

Circulation Research ◽

10.1161/res.127.suppl_1.508 ◽

2020 ◽

Vol 127 (Suppl_1) ◽

Author(s):

Kohta Ikegami ◽

Stefano Secchia ◽

Omar Almakki ◽

Alexis V Stutzman ◽

Sachie Ikegami ◽

...

Keyword(s):

Gene Expression ◽

Histone Acetylation ◽

Binding Sites ◽

Nuclear Periphery ◽

Nuclear Lamina ◽

Lamin A ◽

New Paradigm ◽

Control Of Gene Expression ◽

Nuclear Lamins ◽

Nuclear Interior

The segregation of heterochromatin domains (LADs) at the nuclear periphery by the nuclear lamina, composed by polymerized nuclear Lamin A/C, provides a longstanding paradigm for the control of gene expression and for the mechanisms underlying Lamin-A/C-associated disorders, including progeria and cardiomyopathy. Here, we provide evidence supporting a novel paradigm that Lamin A/C functions as a transcription factor in the nuclear interior. We discovered that Ser22-phosphorylated Lamin A/C (pS22-Lamin A/C), required for lamin depolymerization during mitosis, populated the nuclear interior throughout the cell cycle. pS22-Lamin A/C ChIP-deq demonstrated localization at a large subset of putative active enhancers, not LADs. pS22-Lamin A/C-binding sites were co-occupied by the transcriptional activator c-Jun. In progeria patient-derived fibroblasts, a subset of pS22-Lamin A/C-binding sites were lost whereas new pS22-Lamin A/C-binding sites emerged. New pS22-Lamin A/C binding was accompanied by increased histone acetylation and increased c-Jun binding, whereas loss of pS22-Lamin A/C-binding was accompanied by loss of histone acetylation and c-Jun binding. New pS22-Lamin A/C enhancer binding in progeria was associated with upregulated expression of genes implicated in progeria pathophysiology, including cardiovascular disease. In contrast, alteration of LADs in progeria-patient cells could not explain the observed gene expression changes. These results suggest that Lamin A/C regulates gene expression by enhancer binding in the nuclear interior, independent of its function at the nuclear lamina, providing a new paradigm for the pathogenesis of lamin-associated disorders. pS22-Lamin A/C was also present in the nuclear interior of adult mouse cardiomyocytes. Cardiomyocyte-specific deletion of Lmna encoding Lamin A/C in adult mice caused extensive transcriptional changes in the heart and dilated cardiomyopathy, without apparent reduction of nuclear peripheral Lamin A/C. Disruption of the gene regulatory rather than LAD tethering function of Lamin A/C may underlie the pathogenesis of disorders caused by LMNA mutations, including cardiomyopathy.

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Phosphorylated Lamin A/C in the nuclear interior binds active enhancers associated with abnormal transcription in progeria

10.1101/682260 ◽

2019 ◽

Cited By ~ 1

Author(s):

Kohta Ikegami ◽

Stefano Secchia ◽

Omar Almakki ◽

Jason D. Lieb ◽

Ivan P. Moskowitz

Keyword(s):

Binding Sites ◽

Human Fibroblasts ◽

Nuclear Periphery ◽

Transcriptional Activator ◽

Premature Aging ◽

Lamin A ◽

List Type ◽

Enhancer Activity ◽

Nuclear Interior ◽

Specific Subset

ABSTRACTLMNA encodes nuclear lamin A/C that tethers lamina-associated heterochromatin domains (LADs) to the nuclear periphery. Point mutations in LMNA cause degenerative disorders including the premature aging disorder Hutchinson-Gilford progeria, but the mechanisms are unknown. We report that Ser22-phosphorylated Lamin A/C (pS22-Lamin A/C) was localized to the interior of the nucleus in human fibroblasts throughout the cell cycle. pS22-Lamin A/C interacted with a specific subset of putative active enhancers, not LADs, primarily at locations co-bound by the transcriptional activator c-Jun. In progeria-patient fibroblasts, a subset of pS22-Lamin A/C-binding sites were lost whereas new pS22-Lamin A/C-binding sites emerged in normally quiescent loci. These new pS22-Lamin A/C-binding sites displayed increased histone acetylation and c-Jun binding, implying increased enhancer activity. The genes near these new binding sites, implicated in clinical components of progeria including carotid artery diseases, hypertension, and cardiomegaly, were upregulated in progeria. These results suggest that Lamin A/C regulates gene expression by direct enhancer binding in the nuclear interior. Disruption of the gene regulatory rather than LAD function of Lamin A/C presents a novel mechanism for disorders caused by LMNA mutations including progeria.HIGHLIGHTSpS22-Lamin A/C is present in the nuclear interior throughout interphase.pS22-Lamin A/C associates with active enhancers, not lamina-associated domains.pS22-Lamin A/C-genomic binding sites are co-bound by the transcriptional activator c-Jun.New pS22-Lamin A/C binding in progeria accompanies upregulation of disease-related genes.

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Lamin C is required to establish genome organization after mitosis

Genome Biology ◽

10.1186/s13059-021-02516-7 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Xianrong Wong ◽

Victoria E. Hoskins ◽

Ashley J. Melendez-Perez ◽

Jennifer C. Harr ◽

Molly Gordon ◽

...

Keyword(s):

Genome Organization ◽

Mammalian Cells ◽

Nuclear Periphery ◽

Nuclear Lamina ◽

Lamin A ◽

Chromosome Architecture ◽

3D Genome ◽

Mouse Cells ◽

The Individual ◽

Differential Phosphorylation

Abstract Background The dynamic 3D organization of the genome is central to gene regulation and development. The nuclear lamina influences genome organization through the tethering of lamina-associated domains (LADs) to the nuclear periphery. Evidence suggests that lamins A and C are the predominant lamins involved in the peripheral association of LADs, potentially serving different roles. Results Here, we examine chromosome architecture in mouse cells in which lamin A or lamin C are downregulated. We find that lamin C, and not lamin A, is required for the 3D organization of LADs and overall chromosome organization. Striking differences in localization are present as cells exit mitosis and persist through early G1 and are linked to differential phosphorylation. Whereas lamin A associates with the nascent nuclear envelope (NE) during telophase, lamin C remains in the interior, surrounding globular LAD aggregates enriched on euchromatic regions. Lamin C association with the NE is delayed until several hours into G1 and correlates temporally and spatially with the post-mitotic NE association of LADs. Post-mitotic LAD association with the NE, and global 3D genome organization, is perturbed only in cells depleted of lamin C, and not lamin A. Conclusions Lamin C regulates LAD dynamics during exit from mitosis and is a key regulator of genome organization in mammalian cells. This reveals an unexpectedly central role for lamin C in genome organization, including inter-chromosomal LAD-LAD segregation and LAD scaffolding at the NE, raising intriguing questions about the individual and overlapping roles of lamin A/C in cellular function and disease.

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Microsized Structures Fabricated with Nanoparticles as Building Blocks

MRS Proceedings ◽

10.1557/proc-536-205 ◽

1998 ◽

Vol 536 ◽

Cited By ~ 1

Author(s):

Yongchi Tian ◽

A. D. Dinsmore ◽

S. B. Qadri ◽

B. R. Ratna

Keyword(s):

Radial Growth ◽

Building Blocks ◽

Higher Order ◽

Surfactant Templating ◽

Order Structures

AbstractHere we report a nanoparticulate route to Y2O3 nanofibers (~50 nm in diameter and a few micrometers in length) and for the radial growth of ZnS spheres (200-800 nm diameter). Well-defined higher order structures are developed upon thermostatically aging the dispersions of monomeric nanocrystals. The shapes of the “macromolecules„ are correlated to primary monomeric nanocrystallites, the growing time and temperature, and surfactant templating agents. It is anticipated that this approach should inspire fabrication of nanoparticulate structures by using primary nanoparticles as monomers.

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