A progeria mutation reveals functions for lamin A in nuclear assembly, architecture, and chromosome organization.
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ABSTRACT:
SUBMITTER: Taimen P
PROVIDER: S-EPMC2779830 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:How the same DNA sequences can function in the three-dimensional architecture of interphase nucleus, fold in the very compact structure of metaphase chromosomes and go precisely back to the original interphase architecture in the following cell cycle remains an unresolved question to this day. The strategy used to address this issue was to analyze the correlations between chromosome architecture and the compositional patterns of DNA sequences spanning a size range from a few hundreds to a few thousands Kilobases. This is a critical range that encompasses isochores, interphase chromatin domains and boundaries, and chromosomal bands. The solution rests on the following key points: 1) the transition from the looped domains and sub-domains of interphase chromatin to the 30-nm fiber loops of early prophase chromosomes goes through the unfolding into an extended chromatin structure (probably a 10-nm "beads-on-a-string" structure); 2) the architectural proteins of interphase chromatin, such as CTCF and cohesin sub-units, are retained in mitosis and are part of the discontinuous protein scaffold of mitotic chromosomes; 3) the conservation of the link between architectural proteins and their binding sites on DNA through the cell cycle explains the "mitotic memory" of interphase architecture and the reversibility of the interphase to mitosis process. The results presented here also lead to a general conclusion which concerns the existence of correlations between the isochore organization of the genome and the architecture of chromosomes from interphase to metaphase.
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Project description:The cytoplasmic functions of Wiskott-Aldrich syndrome family (WAS) proteins are well established and include roles in cytoskeleton reorganization and membrane-cytoskeletal interactions important for membrane/vesicle trafficking, morphogenesis, immune response, and signal transduction. Misregulation of these proteins is associated with immune deficiency and metastasis [1-4]. Cytoplasmic WAS proteins act as effectors of Rho family GTPases and polymerize branched actin through the Arp2/3 complex [1, 5]. Previously, we identified Drosophila washout (wash) as a new member of the WAS family with essential cytoplasmic roles in early development [6, 7]. Studies in mammalian cells and Dictyostelium suggest that WASH functions primarily in a multiprotein complex that regulates endosome shape and trafficking in an Arp2/3-dependent manner [8-11]. However, roles for classically cytoplasmic proteins in the nucleus are beginning to emerge, in particular, as participants in the regulation of gene expression [12, 13]. Here, we show that Drosophila Wash is present in the nucleus, where it plays a key role in global nuclear organization. wash mutant and knockdown nuclei disrupt subnuclear structures/organelles and exhibit the abnormal wrinkled morphology reminiscent of those observed in diverse laminopathies [14-16]. We find that nuclear Wash interacts with B-type Lamin (Lamin Dm0), and, like Lamin, Wash associates with constitutive heterochromatin. Wash knockdown increases chromatin accessibility of repressive compartments and results in a global redistribution of repressive histone modifications. Thus, our results reveal a novel role for Wash in modulating nucleus morphology and in the organization of both chromatin and non-chromatin nuclear sub-structures.
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Project description:The nuclear lamina is a meshwork of intermediate-type filament proteins (lamins) that lines the inner nuclear membrane. The lamina is proposed to be an important determinant of nuclear structure, but there has been little direct testing of this idea. To investigate lamina functions, we have characterized a novel lamin B1 mutant lacking the middle approximately 4/5 of its alpha-helical rod domain. Though retaining only 10 heptads of the rod, this mutant assembles into intermediate filament-like structures in vitro. When expressed in cultured cells, it concentrates in patches at the nuclear envelope. Concurrently, endogenous lamins shift from a uniform to a patchy distribution and lose their complete colocalization, and nuclei become highly lobulated. In vitro binding studies suggest that the internal rod region is important for heterotypic associations of lamin B1, which in turn are required for proper organization of the lamina. Accompanying the changes in lamina structure induced by expression of the mutant, nuclear pore complexes and integral membrane proteins of the inner membrane cluster, principally at the patches of endogenous lamins. Considered together, these data indicate that lamins play a major role in organizing other proteins in the nuclear envelope and in determining nuclear shape.
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Project description:Nuclear lamins are ancient type V intermediate filaments with diverse functions that include maintaining nuclear shape, mechanosignaling, tethering and stabilizing chromatin, regulating gene expression, and contributing to cell cycle progression. Despite these numerous roles, an outstanding question has been how lamins are regulated. Accumulating work indicates that a range of lamin post-translational modifications (PTMs) control their functions both in homeostatic cells and in disease states such as progeria, muscular dystrophy, and viral infection. Here, we review the current knowledge of the diverse types of PTMs that regulate lamins in a site-specific manner. We highlight methods that can be used to characterize lamin PTMs whose functions are currently unknown and provide a perspective on the future of the lamin PTM field.
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Project description:Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disease that is frequently caused by a de novo point mutation at position 1824 in LMNA. This mutation activates a cryptic splice donor site in exon 11, and leads to an in-frame deletion within the prelamin A mRNA and the production of a dominant-negative lamin A protein, known as progerin. Here we show that primary HGPS skin fibroblasts experience genome-wide correlated alterations in patterns of H3K27me3 deposition, DNA-lamin A/C associations, and, at late passages, genome-wide loss of spatial compartmentalization of active and inactive chromatin domains. We further demonstrate that the H3K27me3 changes associate with gene expression alterations in HGPS cells. Our results support a model that the accumulation of progerin in the nuclear lamina leads to altered H3K27me3 marks in heterochromatin, possibly through the down-regulation of EZH2, and disrupts heterochromatin-lamina interactions. These changes may result in transcriptional misregulation and eventually trigger the global loss of spatial chromatin compartmentalization in late passage HGPS fibroblasts.
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Project description:This SuperSeries is composed of the SubSeries listed below.
2015-03-10 | GSE59854 | GEO
Project description:Many Lamin A-associated proteins (LAAP's) that are key constituents of the nuclear envelope (NE), assemble at the "core" domains of chromosomes during NE reformation and mitotic exit. However, the identity and function of the chromosomal core domains remain ill-defined. Here, we show that a distinct section of the core domain overlaps with the centromeres/kinetochores of chromosomes during mitotic telophase. The core domain can thus be demarcated into a kinetochore proximal core (KPC) on one side of the segregated chromosomes and the kinetochore distal core (KDC) on the opposite side, close to the central spindle. We next tested if centromere assembly is connected to NE re-formation. We find that centromere assembly is markedly perturbed after inhibiting the function of LMNA and the core-localized LAAPs, BANF1 and Emerin. We also find that the LAAPs exhibit multiple biochemical interactions with the centromere and inner kinetochore proteins. Consistent with this, normal mitotic progression and chromosome segregation was severely impeded after inhibiting LAAP function. Intriguingly, the inhibition of centromere function also interferes with the assembly of LAAP components at the core domain, suggesting a mutual dependence of LAAP and centromeres for their assembly at the core domains. Finally, we find that the localization of key proteins involved in the centromeric loading of CENP-A, including the Mis18 complex and HJURP were markedly affected in LAAP-inhibited cells. Our evidence points to a model where LAAP assembly at the core domain serves a key function in loading new copies of centromeric proteins during or immediately after mitotic exit.
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Project description:The cytoplasmic functions of Wiskott-Aldrich Syndrome family (WASP) proteins are well known and include roles in cytoskeleton reorganization and membrane-cytoskeletal interactions important for membrane/vesicle trafficking, morphogenesis, immune response and signal transduction. Mis-regulation of these proteins is associated with immune deficiency and metastasis. Cytoplasmic WASP proteins act as effectors of Rho family GTPases and polymerize branched actin through the Arp2/3 complex. However, recent evidence has revealed that this classically cytoplasmic protein family also functions in the nucleus. Previously, we identified Drosophila washout (wash) as a new member of the WASP family with essential cytoplasmic roles in early development. Here we show that Wash is also present in the nucleus and plays a key role in nuclear organization via its interaction with Lamin Dm0 at the nuclear envelope. Wash and Lamin Dm0 occupy similar genomic regions that overlap with transcriptionally silent chromatin including constitutive heterochromatin. Strikingly, wash mutant and knockdown nuclei exhibit the same abnormal wrinkled morphology observed in diverse laminopathies, including the Hutchinson-Gilford progeria syndrome, and consistent with disruption of the nuclear organization of several sub-nuclear structures including cajal bodies and the chromocenter in salivary glands. We also found that Wash and Lamin knockdown disrupt chromatin accessibility of repressive compartments in agreement with an observed global redistribution of repressive histone modifications. Functional genetic approaches show wash mutants exhibit similar phenotypes to lamin Dm0 mutants, suggesting they participate in similar regulatory networks. Our results reveal a novel role for Wash in modulating nuclear organization via its interaction with the nuclear envelope protein Lamin Dm0. These findings highlight the functional complexity of WASP family proteins and provide new venues to understand their molecular roles in cell biology and disease. DamID chromatin profiling demostrate that Wash binds similar regions to those bound by Lamin Dm0, in particular transcriptional silent chromatin
2015-03-10 | GSE59853 | GEO
Project description:Hutchinson-Gilford progeria syndrome (HGPS) is an important model disease for premature ageing. Affected children appear healthy at birth, but develop the first symptoms during their first year of life. They die at an average age of 13 years, mostly because of myocardial infarction or stroke. Classical progeria is caused by the heterozygous point mutation c.1824C>T in the LMNA gene, which activates a cryptic splice site. The affected protein cannot be processed correctly to mature lamin A, but is modified into a farnesylated protein truncated by 50 amino acids (progerin). Three more variations in LMNA result in the same mutant protein, but different grades of disease severity. We describe a patient with the heterozygous LMNA mutation c.1821G>A, leading to neonatal progeria with death in the first year of life. Intracellular lamin A was downregulated in the patient's fibroblasts and the ratio of progerin to lamin A was increased when compared with HGPS. It is suggestive that the ratio of farnesylated protein to mature lamin A determines the disease severity in progeria.
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