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1.
J Cell Sci ; 133(11)2020 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-32317396

RESUMO

γ-Tubulin is the main protein involved in the nucleation of microtubules in all eukaryotes. It forms two different complexes with proteins of the GCP family (γ-tubulin complex proteins): γ-tubulin small complexes (γTuSCs) that contain γ-tubulin, and GCPs 2 and 3; and γ-tubulin ring complexes (γTuRCs) that contain multiple γTuSCs in addition to GCPs 4, 5 and 6. Whereas the structure and assembly properties of γTuSCs have been intensively studied, little is known about the assembly of γTuRCs and the specific roles of GCPs 4, 5 and 6. Here, we demonstrate that two copies of GCP4 and one copy each of GCP5 and GCP6 form a salt (KCl)-resistant sub-complex within the γTuRC that assembles independently of the presence of γTuSCs. Incubation of this sub-complex with cytoplasmic extracts containing γTuSCs leads to the reconstitution of γTuRCs that are competent to nucleate microtubules. In addition, we investigate sequence extensions and insertions that are specifically found at the N-terminus of GCP6, and between the GCP6 grip1 and grip2 motifs. We also demonstrate that these are involved in the assembly or stabilization of the γTuRC.


Assuntos
Proteínas Associadas aos Microtúbulos , Tubulina (Proteína) , Centrossomo , Proteínas Associadas aos Microtúbulos/genética , Centro Organizador dos Microtúbulos , Microtúbulos , Tubulina (Proteína)/genética
2.
EMBO J ; 33(2): 114-28, 2014 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-24421324

RESUMO

γ-Tubulin is critical for microtubule (MT) assembly and organization. In metazoa, this protein acts in multiprotein complexes called γ-Tubulin Ring Complexes (γ-TuRCs). While the subunits that constitute γ-Tubulin Small Complexes (γ-TuSCs), the core of the MT nucleation machinery, are essential, mutation of γ-TuRC-specific proteins in Drosophila causes sterility and morphological abnormalities via hitherto unidentified mechanisms. Here, we demonstrate a role of γ-TuRCs in controlling spindle orientation independent of MT nucleation activity, both in cultured cells and in vivo, and examine a potential function for γ-TuRCs on astral MTs. γ-TuRCs locate along the length of astral MTs, and depletion of γ-TuRC-specific proteins increases MT dynamics and causes the plus-end tracking protein EB1 to redistribute along MTs. Moreover, suppression of MT dynamics through drug treatment or EB1 down-regulation rescues spindle orientation defects induced by γ-TuRC depletion. Therefore, we propose a role for γ-TuRCs in regulating spindle positioning by controlling the stability of astral MTs.


Assuntos
Proteínas Associadas aos Microtúbulos/fisiologia , Microtúbulos/metabolismo , Fuso Acromático/fisiologia , Tubulina (Proteína)/fisiologia , Animais , Animais Geneticamente Modificados , Células Cultivadas , Drosophila , Células HeLa , Humanos , Complexos Multiproteicos/fisiologia
3.
Am J Hum Genet ; 96(4): 666-74, 2015 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-25817018

RESUMO

We have identified TUBGCP4 variants in individuals with autosomal-recessive microcephaly and chorioretinopathy. Whole-exome sequencing performed on one family with two affected siblings and independently on another family with one affected child revealed compound-heterozygous mutations in TUBGCP4. Subsequent Sanger sequencing was performed on a panel of individuals from 12 French families affected by microcephaly and ophthalmic manifestations, and one other individual was identified with compound-heterozygous mutations in TUBGCP4. One synonymous variant was common to all three families and was shown to induce exon skipping; the other mutations were frameshift mutations and a deletion. TUBGCP4 encodes γ-tubulin complex protein 4, a component belonging to the γ-tubulin ring complex (γ-TuRC) and known to regulate the nucleation and organization of microtubules. Functional analysis of individual fibroblasts disclosed reduced levels of the γ-TuRC, altered nucleation and organization of microtubules, abnormal nuclear shape, and aneuploidy. Moreover, zebrafish treated with morpholinos against tubgcp4 were found to have reduced head volume and eye developmental anomalies with chorioretinal dysplasia. In summary, the identification of TUBGCP4 mutations in individuals with microcephaly and a spectrum of anomalies in eye development, particularly photoreceptor anomalies, provides evidence of an important role for the γ-TuRC in brain and eye development.


Assuntos
Doenças da Coroide/genética , Oftalmopatias Hereditárias/genética , Microcefalia/genética , Proteínas Associadas aos Microtúbulos/genética , Microtúbulos/genética , Doenças Retinianas/genética , Tubulina (Proteína)/metabolismo , Sequência de Bases , Exoma/genética , Mutação da Fase de Leitura/genética , França , Componentes do Gene , Humanos , Microtúbulos/metabolismo , Dados de Sequência Molecular , Linhagem , Análise de Sequência de DNA
4.
J Biol Chem ; 291(44): 23112-23125, 2016 10 28.
Artigo em Inglês | MEDLINE | ID: mdl-27660388

RESUMO

Microtubules are nucleated from multiprotein complexes containing γ-tubulin and associated γ-tubulin complex proteins (GCPs). Small complexes (γTuSCs) comprise two molecules of γ-tubulin bound to the C-terminal domains of GCP2 and GCP3. γTuSCs associate laterally into helical structures, providing a structural template for microtubule nucleation. In most eukaryotes γTuSCs associate with additional GCPs (4, 5, and 6) to form the core of the so-called γ-tubulin ring complex (γTuRC). GCPs 2-6 constitute a family of homologous proteins. Previous structural analysis and modeling of GCPs suggest that all family members can potentially integrate into the helical structure. Here we provide experimental evidence for this model. Using chimeric proteins in which the N- and C-terminal domains of different GCPs are swapped, we show that the N-terminal domains define the functional identity of GCPs, whereas the C-terminal domains are exchangeable. FLIM-FRET experiments indicate that GCP4 and GCP5 associate laterally within the complex, and their interaction is mediated by their N-terminal domains as previously shown for γTuSCs. Our results suggest that all GCPs are incorporated into the helix via lateral interactions between their N-terminal domains, whereas the C-terminal domains mediate longitudinal interactions with γ-tubulin. Moreover, we show that binding to γ-tubulin is not essential for integrating into the helical complex.


Assuntos
Proteínas Associadas aos Microtúbulos/química , Proteínas Associadas aos Microtúbulos/metabolismo , Tubulina (Proteína)/química , Tubulina (Proteína)/metabolismo , Cristalografia por Raios X , Humanos , Proteínas Associadas aos Microtúbulos/genética , Complexos Multiproteicos/química , Complexos Multiproteicos/genética , Complexos Multiproteicos/metabolismo , Ligação Proteica , Domínios Proteicos , Tubulina (Proteína)/genética
5.
Elife ; 132024 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-38836552

RESUMO

Ninein is a centrosome protein that has been implicated in microtubule anchorage and centrosome cohesion. Mutations in the human NINEIN gene have been linked to Seckel syndrome and to a rare form of skeletal dysplasia. However, the role of ninein in skeletal development remains unknown. Here, we describe a ninein knockout mouse with advanced endochondral ossification during embryonic development. Although the long bones maintain a regular size, the absence of ninein delays the formation of the bone marrow cavity in the prenatal tibia. Likewise, intramembranous ossification in the skull is more developed, leading to a premature closure of the interfrontal suture. We demonstrate that ninein is strongly expressed in osteoclasts of control mice, and that its absence reduces the fusion of precursor cells into syncytial osteoclasts, whereas the number of osteoblasts remains unaffected. As a consequence, ninein-deficient osteoclasts have a reduced capacity to resorb bone. At the cellular level, the absence of ninein interferes with centrosomal microtubule organization, reduces centrosome cohesion, and provokes the loss of centrosome clustering in multinucleated mature osteoclasts. We propose that centrosomal ninein is important for osteoclast fusion, to enable a functional balance between bone-forming osteoblasts and bone-resorbing osteoclasts during skeletal development.


Assuntos
Camundongos Knockout , Proteínas Nucleares , Osteoclastos , Osteogênese , Animais , Camundongos , Centrossomo/metabolismo , Proteínas Nucleares/metabolismo , Proteínas Nucleares/genética , Osteoblastos/metabolismo , Osteoclastos/metabolismo
6.
J Cell Biol ; 172(4): 505-15, 2006 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-16461362

RESUMO

The centrosome is the major microtubule organizing structure in somatic cells. Centrosomal microtubule nucleation depends on the protein gamma-tubulin. In mammals, gamma-tubulin associates with additional proteins into a large complex, the gamma-tubulin ring complex (gammaTuRC). We characterize NEDD1, a centrosomal protein that associates with gammaTuRCs. We show that the majority of gammaTuRCs assemble even after NEDD1 depletion but require NEDD1 for centrosomal targeting. In contrast, NEDD1 can target to the centrosome in the absence of gamma-tubulin. NEDD1-depleted cells show defects in centrosomal microtubule nucleation and form aberrant mitotic spindles with poorly separated poles. Similar spindle defects are obtained by overexpression of a fusion protein of GFP tagged to the carboxy-terminal half of NEDD1, which mediates binding to gammaTuRCs. Further, we show that depletion of NEDD1 inhibits centriole duplication, as does depletion of gamma-tubulin. Our data suggest that centriole duplication requires NEDD1-dependent recruitment of gamma-tubulin to the centrosome.


Assuntos
Centríolos/metabolismo , Centrossomo/metabolismo , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Fuso Acromático/metabolismo , Tubulina (Proteína)/metabolismo , Linhagem Celular , Linhagem Celular Tumoral , Células Cultivadas , Clonagem Molecular , DNA Complementar/genética , Proteínas de Drosophila/genética , Escherichia coli/genética , Células HeLa , Humanos , Ligação Proteica
7.
Nat Commun ; 12(1): 6042, 2021 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-34654813

RESUMO

Centriole biogenesis and maintenance are crucial for cells to generate cilia and assemble centrosomes that function as microtubule organizing centers (MTOCs). Centriole biogenesis and MTOC function both require the microtubule nucleator γ-tubulin ring complex (γTuRC). It is widely accepted that γTuRC nucleates microtubules from the pericentriolar material that is associated with the proximal part of centrioles. However, γTuRC also localizes more distally and in the centriole lumen, but the significance of these findings is unclear. Here we identify spatially and functionally distinct subpopulations of centrosomal γTuRC. Luminal localization is mediated by augmin, which is linked to the centriole inner scaffold through POC5. Disruption of luminal localization impairs centriole integrity and interferes with cilium assembly. Defective ciliogenesis is also observed in γTuRC mutant fibroblasts from a patient suffering from microcephaly with chorioretinopathy. These results identify a non-canonical role of augmin-γTuRC in the centriole lumen that is linked to human disease.


Assuntos
Proteínas de Ciclo Celular/isolamento & purificação , Proteínas de Ciclo Celular/metabolismo , Centríolos/metabolismo , Proteínas Associadas aos Microtúbulos/isolamento & purificação , Proteínas Associadas aos Microtúbulos/metabolismo , Centro Organizador dos Microtúbulos/metabolismo , Animais , Proteínas de Transporte/metabolismo , Proteínas de Ciclo Celular/ultraestrutura , Linhagem Celular , Centríolos/ultraestrutura , Centrossomo/metabolismo , Centrossomo/ultraestrutura , Cílios , Feminino , Humanos , Masculino , Camundongos , Proteínas Associadas aos Microtúbulos/ultraestrutura , Centro Organizador dos Microtúbulos/ultraestrutura , Microtúbulos/metabolismo , Neurônios
8.
Biol Cell ; 101(1): 1-11, 2009 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-19055485

RESUMO

Mitotic spindle formation in animal cells involves microtubule nucleation from two centrosomes that are positioned at opposite sides of the nucleus. Microtubules are captured by the kinetochores and stabilized. In addition, microtubules can be nucleated independently of the centrosome and stabilized by a gradient of Ran-GTP, surrounding the mitotic chromatin. Complex regulation ensures the formation of a bipolar apparatus, involving motor proteins and controlled polymerization and depolymerization of microtubule ends. The bipolar apparatus is, in turn, responsible for faithful chromosome segregation. During recent years, a variety of experiments has indicated that defects in specific motor proteins, centrosome proteins, kinases and other proteins can induce the assembly of aberrant spindles with a monopolar morphology or with poorly separated poles. Induction of monopolar spindles may be a useful strategy for cancer therapy, since ensuing aberrant mitotic exit will usually lead to cell death. In this review, we will discuss the various underlying molecular mechanisms that may be responsible for monopolar spindle formation.


Assuntos
Segregação de Cromossomos , Fuso Acromático/patologia , Animais , Humanos , Proteínas Associadas aos Microtúbulos , Microtúbulos/química , Microtúbulos/metabolismo , Proteínas Motores Moleculares
9.
Mol Cancer ; 8: 10, 2009 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-19243593

RESUMO

BACKGROUND: NEDD1 is a protein that binds to the gamma-tubulin ring complex, a multiprotein complex at the centrosome and at the mitotic spindle that mediates the nucleation of microtubules. RESULTS: We show that NEDD1 is expressed at comparable levels in a variety of tumor-derived cell lines and untransformed cells. We demonstrate that silencing of NEDD1 expression by treatment with siRNA has differential effects on cells, depending on their status of p53 expression: p53-positive cells arrest in G1, whereas p53-negative cells arrest in mitosis with predominantly aberrant monopolar spindles. However, both p53-positive and -negative cells arrest in mitosis if treated with low doses of siRNA against NEDD1 combined with low doses of the inhibitor BI2536 against the mitotic kinase Plk1. Simultaneous reduction of NEDD1 levels and inhibition of Plk1 act in a synergistic manner, by potentiating the anti-mitotic activity of each treatment. CONCLUSION: We propose that NEDD1 may be a promising target for controlling cell proliferation, in particular if targeted in combination with Plk1 inhibitors.


Assuntos
Ciclo Celular/fisiologia , Centrossomo/metabolismo , Proteínas Associadas aos Microtúbulos/fisiologia , Ciclo Celular/efeitos dos fármacos , Ciclo Celular/genética , Proteínas de Ciclo Celular/antagonistas & inibidores , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Citometria de Fluxo , Fase G1/efeitos dos fármacos , Fase G1/genética , Humanos , Linagliptina , Proteínas Associadas aos Microtúbulos/genética , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Proteínas Proto-Oncogênicas/antagonistas & inibidores , Purinas/farmacologia , Quinazolinas/farmacologia , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/fisiologia , Fase de Repouso do Ciclo Celular/efeitos dos fármacos , Fase de Repouso do Ciclo Celular/genética , Proteína Supressora de Tumor p53/metabolismo , Quinase 1 Polo-Like
10.
Open Biol ; 8(3)2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29514869

RESUMO

Microtubules are major constituents of the cytoskeleton in all eukaryotic cells. They are essential for chromosome segregation during cell division, for directional intracellular transport and for building specialized cellular structures such as cilia or flagella. Their assembly has to be controlled spatially and temporally. For this, the cell uses multiprotein complexes containing γ-tubulin. γ-Tubulin has been found in two different types of complexes, γ-tubulin small complexes and γ-tubulin ring complexes. Binding to adaptors and activator proteins transforms these complexes into structural templates that drive the nucleation of new microtubules in a highly controlled manner. This review discusses recent advances on the mechanisms of assembly, recruitment and activation of γ-tubulin complexes at microtubule-organizing centres.


Assuntos
Proteínas Associadas aos Microtúbulos/metabolismo , Centro Organizador dos Microtúbulos/metabolismo , Tubulina (Proteína)/metabolismo , Animais , Divisão Celular , Segregação de Cromossomos , Humanos , Complexos Multiproteicos/metabolismo
11.
Int Rev Cytol ; 238: 1-57, 2004.
Artigo em Inglês | MEDLINE | ID: mdl-15364196

RESUMO

Mitotic and meiotic cells contain a bipolar spindle apparatus of microtubules and associated proteins. To arrange microtubules into focused spindle poles, different mechanisms are used by various organisms. Principally, two major pathways have been characterized: nucleation and anchorage of microtubules at preexisting centers such as centrosomes or spindle pole bodies, or microtubule growth off the surface of chromosomes, followed by sorting and focusing into spindle poles. These two mechanisms can even be found in cells of the same organism: whereas most somatic animal cells utilize the centrosome as an organizing center for spindle microtubules, female meiotic cells build an acentriolar spindle apparatus. Most interestingly, the molecular components that drive acentriolar spindle pole formation are also present in cells containing centrosomes. They include microtubule-dependent motor proteins and a variety of structural proteins that regulate microtubule orientation, anchoring, and stability. The first of these spindle pole proteins, NuMA, had already been identified more than 20 years ago. In addition, several new proteins have been characterized more recently. This review discusses their role during spindle formation and their regulation in the cell cycle.


Assuntos
Proteínas Nucleares/metabolismo , Fuso Acromático , Animais , Antígenos Nucleares , Proteínas de Ciclo Celular , Centrossomo/metabolismo , Proteínas Fúngicas/metabolismo , Humanos , Meiose/fisiologia , Microtúbulos/metabolismo , Mitose/fisiologia , Proteínas Motores Moleculares/metabolismo , Matriz Nuclear/metabolismo , Proteínas Associadas à Matriz Nuclear , Proteínas Nucleares/química , Proteínas Nucleares/genética , Conformação Proteica , Fuso Acromático/fisiologia , Proteína ran de Ligação ao GTP/metabolismo
13.
J Cell Biol ; 193(1): 141-54, 2011 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-21444683

RESUMO

To maintain tissue architecture, epithelial cells divide in a planar fashion, perpendicular to their main polarity axis. As the centrosome resumes an apical localization in interphase, planar spindle orientation is reset at each cell cycle. We used three-dimensional live imaging of GFP-labeled centrosomes to investigate the dynamics of spindle orientation in chick neuroepithelial cells. The mitotic spindle displays stereotypic movements during metaphase, with an active phase of planar orientation and a subsequent phase of planar maintenance before anaphase. We describe the localization of the NuMA and LGN proteins in a belt at the lateral cell cortex during spindle orientation. Finally, we show that the complex formed of LGN, NuMA, and of cortically located Gαi subunits is necessary for spindle movements and regulates the dynamics of spindle orientation. The restricted localization of LGN and NuMA in the lateral belt is instructive for the planar alignment of the mitotic spindle, and required for its planar maintenance.


Assuntos
Proteínas de Transporte/metabolismo , Mitose , Células Neuroepiteliais/metabolismo , Complexo de Proteínas Formadoras de Poros Nucleares/metabolismo , Fuso Acromático/metabolismo , Córtex Visual/metabolismo , Animais , Proteínas de Ciclo Celular , Divisão Celular , Embrião de Galinha , Galinhas , Camundongos , Camundongos Endogâmicos BALB C , Dados de Sequência Molecular , Complexo de Proteínas Formadoras de Poros Nucleares/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa
14.
PLoS One ; 4(6): e5976, 2009 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-19543530

RESUMO

The nucleation of microtubules requires protein complexes containing gamma-tubulin, which are present in the cytoplasm and associate with the centrosome and with the mitotic spindle. We have previously shown that these interactions require the gamma-tubulin targeting factor GCP-WD/NEDD1, which has an essential role in spindle formation. The recruitment of additional gamma-tubulin to the centrosomes occurs during centrosome maturation at the G2/M transition and is regulated by the mitotic kinase Plk1. However, the molecular details of this important pathway are unknown and a Plk1 substrate that controls gamma-tubulin recruitment has not been identified. Here we show that Plk1 associates with GCP-WD in mitosis and Plk1 activity contributes to phosphorylation of GCP-WD. Plk1 depletion or inhibition prevents accumulation of GCP-WD at mitotic centrosomes, but GCP-WD mutants that are defective in Plk1-binding and -phosphorylation still accumulate at mitotic centrosomes and recruit gamma-tubulin. Moreover, Plk1 also controls the recruitment of other PCM proteins implicated in centrosomal gamma-tubulin attachment (Cep192/hSPD2, pericentrin, Cep215/Cdk5Rap2). Our results support a model in which Plk1-dependent recruitment of gamma-tubulin to mitotic centrosomes is regulated upstream of GCP-WD, involves multiple PCM proteins and therefore potentially multiple Plk1 substrates.


Assuntos
Proteínas de Ciclo Celular/metabolismo , Centríolos/metabolismo , Centrossomo/metabolismo , Mitose , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Tubulina (Proteína)/metabolismo , Linhagem Celular Tumoral , Clonagem Molecular , Células HeLa , Humanos , Microscopia de Fluorescência/métodos , Modelos Biológicos , Fosforilação , RNA/química , Interferência de RNA , Fuso Acromático , Quinase 1 Polo-Like
15.
J Cell Sci ; 122(Pt 8): 1134-44, 2009 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-19299467

RESUMO

To investigate changes at the centrosome during the cell cycle, we analyzed the composition of the pericentriolar material from unsynchronized and S-phase-arrested cells by gel electrophoresis and mass spectrometry. We identified HCA66, a protein that localizes to the centrosome from S-phase to mitosis and to the nucleolus throughout interphase. Silencing of HCA66 expression resulted in failure of centrosome duplication and in the formation of monopolar spindles, reminiscent of the phenotype observed after gamma-tubulin silencing. Immunofluorescence microscopy showed that proteins of the gamma-tubulin ring complex were absent from the centrosome in these monopolar spindles. Immunoblotting revealed reduced protein levels of all components of the gamma-tubulin small complex (gamma-tubulin, GCP2, and GCP3) in HCA66-depleted cells. By contrast, the levels of gamma-tubulin ring complex proteins such as GCP4 and GCP-WD/NEDD1 were unaffected. We propose that HCA66 is a novel regulator of gamma-tubulin function that plays a role in stabilizing components of the gamma-tubulin small complex, which is in turn essential for assembling the larger gamma-tubulin ring complex.


Assuntos
Antígenos de Neoplasias/metabolismo , Proteínas de Transporte/metabolismo , Ciclo Celular , Nucléolo Celular/metabolismo , Centrossomo/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Tubulina (Proteína)/metabolismo , Antígenos de Neoplasias/genética , Proteínas de Transporte/genética , Eletroforese em Gel de Poliacrilamida , Células HeLa , Humanos , Células Jurkat , Espectrometria de Massas , Microscopia de Fluorescência , Complexos Multiproteicos/metabolismo , Ligação Proteica , Estabilidade Proteica , Interferência de RNA , RNA Interferente Pequeno/metabolismo , Proteínas de Ligação a RNA , Proteínas Recombinantes de Fusão/metabolismo , Fatores de Tempo , Transfecção
16.
BMC Res Notes ; 2: 64, 2009 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-19400937

RESUMO

BACKGROUND: NuMA is a protein that has been previously shown to play a role in focusing microtubules at the mitotic spindle poles. However, most previous work relies on experimental methods that might cause dominant side effects on spindle formation, such as microinjection of antibodies, overexpression of mutant protein, or immunodepletion of NuMA-containing protein complexes. FINDINGS: To circumvent these technical problems, we performed siRNA experiments in which we depleted the majority of NuMA in human cultured cells. Depleted mitotic cells show a prolonged duration of prometaphase, with spindle pole defects and with unattached, unaligned chromosomes. CONCLUSION: Our data confirm that NuMA is important for spindle pole formation, and for cohesion of centrosome-derived microtubules with the bulk of spindle microtubules. Our findings of NuMA-dependent defects in chromosome alignment suggest that NuMA is involved in stabilizing kinetochore fibres.

17.
J Cell Sci ; 115(Pt 9): 1815-24, 2002 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-11956313

RESUMO

In mitosis, NuMA localises to spindle poles where it contributes to the formation and maintenance of focussed microtubule arrays. Previous work has shown that NuMA is transported to the poles by dynein and dynactin. So far, it is unclear how NuMA accumulates at the spindle poles following transport and how it remains associated throughout mitosis. We show here that NuMA can bind to microtubules independently of dynein/dynactin. We characterise a 100-residue domain located within the C-terminal tail of NuMA that mediates a direct interaction with tubulin in vitro and that is necessary for NuMA association with tubulin in vivo. Moreover, this domain induces bundling and stabilisation of microtubules when expressed in cultured cells and leads to formation of abnormal mitotic spindles with increased microtubule asters or multiple poles. Our results suggest that NuMA organises the poles by stable crosslinking of the microtubule fibers.


Assuntos
Divisão Celular/fisiologia , Células Eucarióticas/metabolismo , Microtúbulos/metabolismo , Proteínas Nucleares/metabolismo , Tubulina (Proteína)/metabolismo , Proteínas de Xenopus , Motivos de Aminoácidos/fisiologia , Sequência de Aminoácidos/fisiologia , Animais , Antígenos Nucleares , Proteínas de Ciclo Celular , Complexo Dinactina , Dineínas/metabolismo , Células Eucarióticas/citologia , Feminino , Células HeLa , Humanos , Proteínas Associadas aos Microtúbulos/metabolismo , Modelos Biológicos , Proteínas Associadas à Matriz Nuclear , Oócitos , Fragmentos de Peptídeos/metabolismo , Ligação Proteica/fisiologia , Fuso Acromático/metabolismo , Xenopus laevis
18.
EMBO Rep ; 5(1): 97-103, 2004 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-14710193

RESUMO

The protein NuMA localizes to mitotic spindle poles where it contributes to the organization of microtubules. In this study, we demonstrate that NuMA loses its stable association with the spindle poles after anaphase onset. Using extracts from Xenopus laevis eggs, we show that NuMA is dephosphorylated in anaphase and released from dynein and dynactin. In the presence of a nondegradable form of cyclin B (Delta90), NuMA remains phosphorylated and associated with dynein and dynactin, and remains localized to stable spindle poles that fail to disassemble at the end of mitosis. Inhibition of NuMA or dynein allows completion of mitosis, despite inducing spindle pole abnormalities. We propose that NuMA functions early in mitosis during the formation of spindle poles, but is released from the spindle after anaphase, to allow spindle disassembly and remodelling of the microtubule network.


Assuntos
Ciclina B/metabolismo , Dineínas/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas Nucleares/metabolismo , Fuso Acromático/fisiologia , Proteínas de Xenopus/metabolismo , Anáfase , Animais , Temperatura Baixa , Complexo Dinactina , Células HeLa , Humanos , Imunoprecipitação , Microinjeções , Microtúbulos/metabolismo , Microtúbulos/ultraestrutura , Fuso Acromático/ultraestrutura , Xenopus laevis
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