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  • American Society for Cell Biology (ASCB)  (110)
  • 1
    Online Resource
    Online Resource
    Lamin-B1 contributes to the proper timing of epicardial cell migration and function during embryonic heart development
    American Society for Cell Biology (ASCB) ; 2016
    In:  Molecular Biology of the Cell Vol. 27, No. 25 ( 2016-12-15), p. 3956-3963
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 27, No. 25 ( 2016-12-15), p. 3956-3963
    Abstract: Lamin proteins form a meshwork beneath the nuclear envelope and contribute to many different cellular processes. Mutations in lamins cause defective organogenesis in mouse models and human diseases that affect adipose tissue, brain, skeletal muscle, and the heart. In vitro cell culture studies have shown that lamins help maintain nuclear shape and facilitate cell migration. However, whether these defects contribute to improper tissue building in vivo requires further clarification. By studying the heart epicardium during embryogenesis, we show that Lb1-null epicardial cells exhibit in vivo and in vitro migratory delay. Transcriptome analyses of these cells suggest that Lb1 influences the expression of cell adhesion genes, which could affect cell migration during epicardium development. These epicardial defects are consistent with incomplete development of both vascular smooth muscle and compact myocardium at later developmental stages in Lb1-null embryos. Further, we found that Lb1-null epicardial cells have a delayed nuclear morphology change in vivo, suggesting that Lb1 facilitates morphological changes associated with migration. These findings suggest that Lb1 contributes to nuclear shape maintenance and migration of epicardial cells and highlights the use of these cells for in vitro and in vivo study of these classic cell biological phenomena.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.E16-06-0462
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2016
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  • 2
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    Online Resource
    Identification of lamin B–regulated chromatin regions based on chromatin landscapes
    American Society for Cell Biology (ASCB) ; 2015
    In:  Molecular Biology of the Cell Vol. 26, No. 14 ( 2015-07-05), p. 2685-2697
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 26, No. 14 ( 2015-07-05), p. 2685-2697
    Abstract: Lamins, the major structural components of the nuclear lamina (NL) found beneath the nuclear envelope, are known to interact with most of the nuclear peripheral chromatin in metazoan cells. Although NL–chromatin associations correlate with a repressive chromatin state, the role of lamins in tethering chromatin to NL and how such tether influences gene expression have remained challenging to decipher. Studies suggest that NL proteins regulate chromatin in a context-dependent manner. Therefore understanding the context of chromatin states based on genomic features, including chromatin–NL interactions, is important to the study of lamins and other NL proteins. By modeling genome organization based on combinatorial patterns of chromatin association with lamin B1, core histone modification, and core and linker histone occupancy, we report six distinct large chromatin landscapes, referred to as histone lamin landscapes (HiLands)-red (R), -orange (O), -yellow (Y), -green (G), -blue (B), and -purple (P), in mouse embryonic stem cells (mESCs). This HiLands model demarcates the previously mapped lamin-associated chromatin domains (LADs) into two HiLands, HiLands-B and HiLands-P, which are similar to facultative and constitutive heterochromatins, respectively. Deletion of B-type lamins in mESCs caused a reduced interaction between regions of HiLands-B and NL as measured by emerin–chromatin interaction. Our findings reveal the importance of analyzing specific chromatin types when studying the function of NL proteins in chromatin tether and regulation.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.E15-04-0210
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2015
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  • 3
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    Online Resource
    Multisite phosphorylation determines the formation of Ska–Ndc80 macro-complexes that are essential for chromosome segregation during mitosis
    American Society for Cell Biology (ASCB) ; 2020
    In:  Molecular Biology of the Cell Vol. 31, No. 17 ( 2020-08-01), p. 1892-1903
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 31, No. 17 ( 2020-08-01), p. 1892-1903
    Abstract: The human Ska complex (Ska) localizing to both spindle microtubules and kinetochores is essential for proper chromosome segregation during mitosis. Although several mechanisms have been proposed to explain how Ska is recruited to kinetochores, it is still not fully understood. By analyzing Ska3 phosphorylation, we identified six critical Cdk1 sites, including the previously identified Thr358 and Thr360. Mutations of these sites to phospho-deficient alanine (6A) in cells completely abolished Ska3 localization to kinetochores and Ska functions in chromosome segregation. In vitro, Cdk1 phosphorylation on Ska enhanced WT, not phospho-deficient 6A, binding to Ndc80C. Strikingly, the phosphomimetic Ska 6D complex formed a stable macro-complex with Ndc80C, but Ska WT failed to do so. These results suggest that multisite Cdk1 phosphorylation-enabled Ska–Ndc80 binding is decisive for Ska localization to kinetochores and its functions. Moreover, we found that Ska decrease at kinetochores triggered by the microtubule-depolymerizing drug nocodazole is independent of Aurora B but can be overridden by Ska3 overexpression, suggestive of a role of spindle microtubules in promoting Ska kinetochore recruitment. Thus, based on the current and previous results, we propose that multisite Cdk1 phosphorylation is critical for the formation of Ska–Ndc80 macro-complexes that are essential for chromosome segregation.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.E19-10-0569
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2020
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  • 4
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    Online Resource
    Characterization of a New γTuRC Subunit with WD Repeats
    American Society for Cell Biology (ASCB) ; 2003
    In:  Molecular Biology of the Cell Vol. 14, No. 3 ( 2003-03), p. 1017-1026
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 14, No. 3 ( 2003-03), p. 1017-1026
    Abstract: The γ-tubulin ring complex (γTuRC), consisting of multiple protein subunits, can nucleate microtubule assembly. Although many subunits of the γTuRC have been identified, a complete set remains to be defined in any organism. In addition, how the subunits interact with each other to assemble into γTuRC remains largely unknown. Here, we report the characterization of a novel γTuRC subunit, Drosophila gamma ring protein with WD repeats (Dgp71WD). With the exception of γ-tubulin, Dgp71WD is the only γTuRC component identified to date that does not contain the grip motifs, which are signature sequences conserved in γTuRC components. By performing immunoprecipitations after pair-wise coexpression in Sf9 cells, we show that Dgp71WD directly interacts with the grip motif–containing γTuRC subunits, Dgrips84, 91, 128, and 163, suggesting that Dgp71WD may play a scaffolding role in γTuRC organization. We also show that Dgrips128 and 163, like Dgrips84 and 91, can interact directly with γ-tubulin. Coexpression of any of these grip motif–containing proteins with γ-tubulin promotes γ-tubulin binding to guanine nucleotide. In contrast, in the same assay Dgp71WD interacts with γ-tubulin but does not facilitate nucleotide binding.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e02-01-0034
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2003
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  • 5
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    Online Resource
    Ste20-related Protein Kinase LOSK (SLK) Controls Microtubule Radial Array in Interphase
    American Society for Cell Biology (ASCB) ; 2008
    In:  Molecular Biology of the Cell Vol. 19, No. 5 ( 2008-05), p. 1952-1961
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 19, No. 5 ( 2008-05), p. 1952-1961
    Abstract: Interphase microtubules are organized into a radial array with centrosome in the center. This organization is a subject of cellular regulation that can be driven by protein phosphorylation. Only few protein kinases that regulate microtubule array in interphase cells have been described. Ste20-like protein kinase LOSK (SLK) was identified as a microtubule and centrosome-associated protein. In this study we have shown that the inhibition of LOSK activity by dominant-negative mutant K63R-ΔT or by LOSK depletion with RNAi leads to unfocused microtubule arrangement. Microtubule disorganization is prominent in Vero, CV-1, and CHO-K1 cells but less distinct in HeLa cells. The effect is a result neither of microtubule stabilization nor of centrosome disruption. In cells with suppressed LOSK activity centrosomes are unable to anchor or to cap microtubules, though they keep nucleating microtubules. These centrosomes are depleted of dynactin. Vero cells overexpressing K63R-ΔT have normal dynactin “comets” at microtubule ends and unaltered morphology of Golgi complex but are unable to polarize it at the wound edge. We conclude that protein kinase LOSK is required for radial microtubule organization and for the proper localization of Golgi complex in various cell types.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e06-12-1156
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2008
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  • 6
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    Online Resource
    The Drosophila Kinesin-13, KLP59D, Impacts Pacman- and Flux-based Chromosome Movement
    American Society for Cell Biology (ASCB) ; 2009
    In:  Molecular Biology of the Cell Vol. 20, No. 22 ( 2009-11-15), p. 4696-4705
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 20, No. 22 ( 2009-11-15), p. 4696-4705
    Abstract: Chromosome movements are linked to the active depolymerization of spindle microtubule (MT) ends. Here we identify the kinesin-13 family member, KLP59D, as a novel and uniquely important regulator of spindle MT dynamics and chromosome motility in Drosophila somatic cells. During prometaphase and metaphase, depletion of KLP59D, which targets to centrosomes and outer kinetochores, suppresses the depolymerization of spindle pole–associated MT minus ends, thereby inhibiting poleward tubulin Flux. Subsequently, during anaphase, loss of KLP59D strongly attenuates chromatid-to-pole motion by suppressing the depolymerization of both minus and plus ends of kinetochore-associated MTs. The mechanism of KLP59D's impact on spindle MT plus and minus ends appears to differ. Our data support a model in which KLP59D directly depolymerizes kinetochore-associated plus ends during anaphase, but influences minus ends indirectly by localizing the pole-associated MT depolymerase KLP10A. Finally, electron microscopy indicates that, unlike the other Drosophila kinesin-13s, KLP59D is largely incapable of oligomerizing into MT-associated rings in vitro, suggesting that such structures are not a requisite feature of kinetochore-based MT disassembly and chromosome movements.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e09-07-0557
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2009
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  • 7
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    APC FZR1 prevents nondisjunction in mouse oocytes by controlling meiotic spindle assembly timing
    American Society for Cell Biology (ASCB) ; 2012
    In:  Molecular Biology of the Cell Vol. 23, No. 20 ( 2012-10-15), p. 3970-3981
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 23, No. 20 ( 2012-10-15), p. 3970-3981
    Abstract: FZR1 is an anaphase-promoting complex (APC) activator best known for its role in the mitotic cell cycle at M-phase exit, in G1, and in maintaining genome integrity. Previous studies also established that it prevents meiotic resumption, equivalent to the G2/M transition. Here we report that mouse oocytes lacking FZR1 undergo passage through meiosis I that is accelerated by ∼1 h, and this is due to an earlier onset of spindle assembly checkpoint (SAC) satisfaction and APC CDC20 activity. However, loss of FZR1 did not compromise SAC functionality; instead, earlier SAC satisfaction was achieved because the bipolar meiotic spindle was assembled more quickly in the absence of FZR1. This novel regulation of spindle assembly by FZR1 led to premature bivalent attachment to microtubules and loss of kinetochore-bound MAD2. Bivalents, however, were observed to congress poorly, leading to nondisjunction rates of 25%. We conclude that in mouse oocytes FZR1 controls the timing of assembly of the bipolar spindle and in so doing the timing of SAC satisfaction and APC CDC20 activity. This study implicates FZR1 as a major regulator of prometaphase whose activity helps to prevent chromosome nondisjunction.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e12-05-0352
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2012
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  • 8
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    Online Resource
    Coordinated increase of nuclear tension and lamin-A with matrix stiffness outcompetes lamin-B receptor that favors soft tissue phenotypes
    American Society for Cell Biology (ASCB) ; 2017
    In:  Molecular Biology of the Cell Vol. 28, No. 23 ( 2017-11-07), p. 3333-3348
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 28, No. 23 ( 2017-11-07), p. 3333-3348
    Abstract: Matrix stiffness that is sensed by a cell or measured by a purely physical probe reflects the intrinsic elasticity of the matrix and also how thick or thin the matrix is. Here, mesenchymal stem cells (MSCs) and their nuclei spread in response to thickness-corrected matrix microelasticity, with increases in nuclear tension and nuclear stiffness resulting from increases in myosin-II and lamin-A,C. Linearity between the widely varying projected area of a cell and its nucleus across many matrices, timescales, and myosin-II activity levels indicates a constant ratio of nucleus-to-cell volume, despite MSCs’ lineage plasticity. Nuclear envelope fluctuations are suppressed on the stiffest matrices, and fluctuation spectra reveal a high nuclear tension that matches trends from traction force microscopy and from increased lamin-A,C. Transcriptomes of many diverse tissues and MSCs further show that lamin-A,C’s increase with tissue or matrix stiffness anti-correlates with lamin-B receptor (LBR), which contributes to lipid/sterol biosynthesis. Adipogenesis (a soft lineage) indeed increases LBR:lamin-A,C protein stoichiometry in MSCs versus osteogenesis (stiff). The two factors compete for lamin-B in response to matrix elasticity, knockdown, myosin-II inhibition, and even constricted migration that disrupts and segregates lamins in situ. Matrix stiffness-driven contractility thus tenses the nucleus to favor lamin-A,C accumulation and suppress soft tissue phenotypes.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e17-06-0393
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2017
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  • 9
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    Online Resource
    Distinct and Temporal Roles of Nucleosomal Remodeling and Histone Deacetylation in the Repression of the hTERT Gene
    American Society for Cell Biology (ASCB) ; 2010
    In:  Molecular Biology of the Cell Vol. 21, No. 5 ( 2010-03), p. 821-832
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 21, No. 5 ( 2010-03), p. 821-832
    Abstract: hTERT, the human telomerase reverse transcriptase, is highly expressed in stem cells and embryonic tissues but undetectable in most adult somatic cells. To understand its repression mechanisms in somatic cells, we investigated the endogenous hTERT gene regulation during differentiation of human leukemic HL60 cells. Our study revealed that silencing of the hTERT promoter was a biphasic process. Within 24 h after initiation of differentiation, hTERT mRNA expression decreased dramatically, accompanied by increased expression of Mad1 gene and disappearance of a nucleosome-free region at the hTERT core promoter. Subsequent to this early repression, nucleosomal remodeling continued at the promoter and downstream region for several days, as demonstrated by micrococcal nuclease and restriction enzyme accessibility assays. This later nucleosomal remodeling correlated with stable silencing of the hTERT promoter. Progressive changes of core histone modifications occurred throughout the entire differentiation process. Surprisingly, inhibition of histone deacetylation at the hTERT promoter did not prevent hTERT repression or nucleosomal deposition, indicating that nucleosomal deposition at the core promoter, but not histone deacetylation, was the cause of transcriptional repression. Our data also suggested that succeeding nucleosomal remodeling and histone deacetylation worked in parallel to establish the stable repressive status of hTERT gene in human somatic cells.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e09-06-0456
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2010
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  • 10
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    Online Resource
    Proper Recruitment of γ-Tubulin and D-TACC/Msps to Embryonic Drosophila Centrosomes Requires Centrosomin Motif 1
    American Society for Cell Biology (ASCB) ; 2007
    In:  Molecular Biology of the Cell Vol. 18, No. 10 ( 2007-10), p. 4037-4049
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 18, No. 10 ( 2007-10), p. 4037-4049
    Abstract: Centrosomes are microtubule-organizing centers and play a dominant role in assembly of the microtubule spindle apparatus at mitosis. Although the individual binding steps in centrosome maturation are largely unknown, Centrosomin (Cnn) is an essential mitotic centrosome component required for assembly of all other known pericentriolar matrix (PCM) proteins to achieve microtubule-organizing activity at mitosis in Drosophila. We have identified a conserved motif (Motif 1) near the amino terminus of Cnn that is essential for its function in vivo. Cnn Motif 1 is necessary for proper recruitment of γ-tubulin, D-TACC (the homolog of vertebrate transforming acidic coiled-coil proteins [TACC]), and Mini spindles (Msps) to embryonic centrosomes but is not required for assembly of other centrosome components including Aurora A kinase and CP60. Centrosome separation and centrosomal satellite formation are severely disrupted in Cnn Motif 1 mutant embryos. However, actin organization into pseudocleavage furrows, though aberrant, remains partially intact. These data show that Motif 1 is necessary for some but not all of the activities conferred on centrosome function by intact Cnn.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e07-05-0474
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2007
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