共查询到20条相似文献，搜索用时 15 毫秒
1.
Azimzadeh J Wong ML Downhour DM Sánchez Alvarado A Marshall WF 《Science (New York, N.Y.)》2012,335(6067):461-463
The centrosome, a cytoplasmic organelle formed by cylinder-shaped centrioles surrounded by a microtubule-organizing matrix, is a hallmark of animal cells. The centrosome is conserved and essential for the development of all animal species described so far. Here, we show that planarians, and possibly other flatworms, lack centrosomes. In planarians, centrioles are only assembled in terminally differentiating ciliated cells through the acentriolar pathway to trigger the assembly of cilia. We identified a large set of conserved proteins required for centriole assembly in animals and note centrosome protein families that are missing from the planarian genome. Our study uncovers the molecular architecture and evolution of the animal centrosome and emphasizes the plasticity of animal cell biology and development. 相似文献
2.
As an organelle coupling nuclear and cytoplasmic divisions, the centrosome is essential to mitotic fidelity, and its inheritance could be critical to understanding cell transformation. Investigating the behavior of the centrosome in living mitotic cells, we documented a transient and remarkable postanaphase repositioning of this organelle, which apparently controls the release of central microtubules from the midbody and the completion of cell division. We also observed that the absence of the centrosome leads to defects in cytokinesis. Together with recent results in yeasts, our data point to a conserved centrosome-dependent pathway that integrates spatial controls into the decision of completing cell division, which requires the repositioning of the centrosome organelle. 相似文献
3.
Chan JR Jolicoeur C Yamauchi J Elliott J Fawcett JP Ng BK Cayouette M 《Science (New York, N.Y.)》2006,314(5800):832-836
Cell polarity is critical in various cellular processes ranging from cell migration to asymmetric cell division and axon and dendrite specification. Similarly, myelination by Schwann cells is polarized, but the mechanisms involved remain unclear. Here, we show that the polarity protein Par-3 localizes asymmetrically in Schwann cells at the axon-glial junction and that disruption of Par-3 localization, by overexpression and knockdown, inhibits myelination. Additionally, we show that Par-3 directly associates and recruits the p75 neurotrophin receptor to the axon-glial junction, forming a complex necessary for myelination. Together, these results point to a critical role in the establishment of cell polarity for myelination. 相似文献
4.
In both animal and yeast cells, signaling pathways involving small guanosine triphosphatases (GTPases) regulate polarized organization of the actin cytoskeleton. In the budding yeast Saccharomyces cerevisiae, the Ras-like GTPase Bud1/Rsr1 and its guanosine 5'-diphosphate (GDP)/guanosine 5'-triphosphate (GTP) exchange factor Bud5 are involved in the selection of a specific site for growth, thus determining cell polarity. We found that Bud5 is localized at the cell division site and the presumptive bud site. Its localization is dependent on potential cellular landmarks, such as Bud3 and Axl2/Bud10 in haploid cells and Bud8 and Bud9 in diploid cells. Bud5 also physically interacts with Axl2/Bud10, a transmembrane glycoprotein, suggesting that a receptor-like transmembrane protein recruits a GDP/GTP exchange factor to connect an intrinsic spatial signal to oriented cell growth. 相似文献
5.
Parallels between cytokinesis and retroviral budding: a role for the ESCRT machinery 总被引：1，自引：0，他引：1
During cytokinesis, as dividing animal cells pull apart into two daughter cells, the final stage, termed abscission, requires breakage of the midbody, a thin membranous stalk connecting the daughter cells. This membrane fission event topologically resembles the budding of viruses, such as HIV-1, from infected cells. We found that two proteins involved in HIV-1 budding-tumor susceptibility gene 101 (Tsg101), a subunit of the endosomal sorting complex required for transport I (ESCRT-I), and Alix, an ESCRT-associated protein-were recruited to the midbody during cytokinesis by interaction with centrosome protein 55 (Cep55), a centrosome and midbody protein essential for abscission. Tsg101, Alix, and possibly other components of ESCRT-I were required for the completion of cytokinesis. Thus, HIV-1 budding and cytokinesis use a similar subset of cellular components to carry out topologically similar membrane fission events. 相似文献
6.
Aberrant centrosome duplication is observed in many tumor cells and may contribute to genomic instability through the formation of multipolar mitotic spindles. Cyclin-dependent kinase 2 (Cdk2) is required for multiple rounds of centrosome duplication in Xenopus egg extracts but not for the initial round of replication. Egg extracts undergo periodic oscillations in the level of free calcium. We show here that chelation of calcium in egg extracts or specific inactivation of calcium/calmodulin-dependent protein kinase II (CaMKII) blocks even initial centrosome duplication, whereas inactivation of Cdk2 does not. Duplication can be restored to inhibited extracts by addition of CaMKII and calmodulin. These results indicate that calcium, calmodulin, and CaMKII are required for an essential step in initiation of centrosome duplication. Our data suggest that calcium oscillations in the cell cycle may be linked to centrosome duplication. 相似文献
7.
Adult stem cells often divide asymmetrically to produce one self-renewed stem cell and one differentiating cell, thus maintaining both populations. The asymmetric outcome of stem cell divisions can be specified by an oriented spindle and local self-renewal signals from the stem cell niche. Here we show that developmentally programmed asymmetric behavior and inheritance of mother and daughter centrosomes underlies the stereotyped spindle orientation and asymmetric outcome of stem cell divisions in the Drosophila male germ line. The mother centrosome remains anchored near the niche while the daughter centrosome migrates to the opposite side of the cell before spindle formation. 相似文献
8.
胚胎干细胞(Embryonicstemcells,ES细胞)是从早期胚胎内细胞团(innercellmassICM)或原始生殖细胞(Primordialgermcells,PGCs)经体外分化抑制培养分离克隆的。ES细胞在动物克隆、转基因动物生产、细胞工程、组织工程、临床克隆治疗和发育生物学等的研究应用中起着重要的作用。本文介绍了胚胎干细胞的生物学特性,国内外研究进展和研究动态。阐明了建立ES细胞系的技术要点以及ES细胞的应用及发展前景。 相似文献
9.
Cadherin cell adhesion receptors as a morphogenetic regulator 总被引：250，自引：0，他引：250
M Takeichi 《Science (New York, N.Y.)》1991,251(5000):1451-1455
Cadherins are a family of cell adhesion receptors that are crucial for the mutual association of vertebrate cells. Through their homophilic binding interactions, cadherins play a role in cell-sorting mechanisms, conferring adhesion specificities on cells. The regulated expression of cadherins also controls cell polarity and tissue morphology. Cadherins are thus considered to be important regulators of morphogenesis. Moreover, pathological examinations suggest that the down-regulation of cadherin expression is associated with the invasiveness of tumor cells. 相似文献
10.
The spindle assembly checkpoint guards the fidelity of chromosome segregation. It requires the close cooperation of cell cycle regulatory proteins and cytoskeletal elements to sense spindle integrity. The role of the centrosome, the organizing center of the microtubule cytoskeleton, in the spindle checkpoint is unclear. We found that the molecular requirements for a functional spindle checkpoint included components of the large gamma-tubulin ring complex (gamma-TuRC). However, their localization at the centrosome and centrosome integrity were not essential for this function. Thus, the spindle checkpoint can be activated at the level of microtubule nucleation. 相似文献
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12.
利用生长素极性运输转运蛋白PIN1与增强绿色荧光蛋白EGFP的融合,对PIN1进行了荧光标记,并以烟草表皮毛为模式,开展了PIN1对生长素极性运输及对细胞伸长生长影响的研究。采用DNA重组技术,将融合标记基因EGFP–PIN1置于拟南芥表皮毛特异表达基因GL2的启动子调控下,构建成含GL2pro::EGFP–PIN1的Ti质粒,以根癌农杆菌叶盘共培转化法将重组标记基因转化至烟草WS38中,筛选鉴定出多株转基因烟草。通过对这些转基因烟草表皮毛进行显微荧光观察,结果发现,标记的绿色荧光信号集中分布在表皮毛细胞的间隔区,表现为明显的极性分布现象。用生长素极性运输抑制剂三碘苯甲酸(TIBA)处理后,表皮毛的伸长生长受到抑制,细胞中荧光的分布极性减弱。说明生长素在烟草表皮毛中的极性分布对烟草表皮毛伸长起关键作用,抑制生长素的极性运输不只抑制表皮毛的细胞伸长,同时还影响到生长素极性运输蛋白PIN的极性分布。 相似文献
13.
Excess cyclin E-Cdk2 accelerates entry into S phase of the cell cycle and promotes polyploidy, which may contribute to genomic instability in cancer cells. We identified 20 amino acids in cyclin E as a centrosomal localization signal (CLS) essential for both centrosomal targeting and promoting DNA synthesis. Expressed wild-type, but not mutant, CLS peptides localized on the centrosome, prevented endogenous cyclin E and cyclin A from localizing to the centrosome, and inhibited DNA synthesis. Ectopic cyclin E localized to the centrosome and accelerated S phase entry even with mutations that abolish Cdk2 binding, but not with a mutation in the CLS. These results suggest that cyclin E has a modular centrosomal-targeting domain essential for promoting S phase entry in a Cdk2-independent manner. 相似文献
14.
Early embryos of some metazoans polarize radially to facilitate critical patterning events such as gastrulation and asymmetric cell division; however, little is known about how radial polarity is established. Early embryos of Caenorhabditis elegans polarize radially when cell contacts restrict the polarity protein PAR-6 to contact-free cell surfaces, where PAR-6 regulates gastrulation movements. We have identified a Rho guanosine triphosphatase activating protein (RhoGAP), PAC-1, which mediates C. elegans radial polarity and gastrulation by excluding PAR-6 from contacted cell surfaces. We show that PAC-1 is recruited to cell contacts, and we suggest that PAC-1 controls radial polarity by restricting active CDC-42 to contact-free surfaces, where CDC-42 binds and recruits PAR-6. Thus, PAC-1 provides a dynamic molecular link between cell contacts and PAR proteins that polarizes embryos radially. 相似文献
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16.
Quintyne NJ Reing JE Hoffelder DR Gollin SM Saunders WS 《Science (New York, N.Y.)》2005,307(5706):127-129
Most tumor cells are characterized by increased genomic instability and chromosome segregational defects, often associated with hyperamplification of the centrosome and the formation of multipolar spindles. However, extra centrosomes do not always lead to multipolarity. Here, we describe a process of centrosomal clustering that prevented the formation of multipolar spindles in noncancer cells. Noncancer cells needed to overcome this clustering mechanism to allow multipolar spindles to form at a high frequency. The microtubule motor cytoplasmic dynein was a critical part of this coalescing machinery, and in some tumor cells overexpression of the spindle protein NuMA interfered with dynein localization, promoting multipolarity. 相似文献
17.
Lee L Tirnauer JS Li J Schuyler SC Liu JY Pellman D 《Science (New York, N.Y.)》2000,287(5461):2260-2262
Correct positioning of the mitotic spindle is critical for cell division and development. Spindle positioning involves a search-and-capture mechanism whereby dynamic microtubules find and then interact with specific sites on the submembrane cortex. Genetic, biochemical, and imaging experiments suggest a mechanism for cortical-microtubule capture. Bim1p, located at microtubule distal ends, bound Kar9p, a protein associated with the daughter cell cortex. Bim1p is the yeast ortholog of human EB1, a binding partner for the adenomatous polyposis coli tumor suppressor. EB1 family proteins may have a general role in linking the microtubule cytoskeleton to cortical polarity determinants. 相似文献
18.
Amonlirdviman K Khare NA Tree DR Chen WS Axelrod JD Tomlin CJ 《Science (New York, N.Y.)》2005,307(5708):423-426
Planar cell polarity (PCP) signaling generates subcellular asymmetry along an axis orthogonal to the epithelial apical-basal axis. Through a poorly understood mechanism, cell clones that have mutations in some PCP signaling components, including some, but not all, alleles of the receptor frizzled, cause polarity disruptions of neighboring wild-type cells, a phenomenon referred to as domineering nonautonomy. Here, a contact-dependent signaling hypothesis, derived from experimental results, is shown by reaction-diffusion, partial differential equation modeling and simulation to fully reproduce PCP phenotypes, including domineering nonautonomy, in the Drosophila wing. The sufficiency of this model and the experimental validation of model predictions reveal how specific protein-protein interactions produce autonomy or domineering nonautonomy. 相似文献
19.
利用石蜡切片法对丹参不同时期花器官进行了解剖学研究。结果表明:丹参单珠被,薄珠心,倒生胚珠,有承珠盘结构。孢原细胞位于珠心一层表皮下,直接行使大孢子母细胞功能。大孢子母细胞减数分裂合点端或合点端第二个大孢子为功能大孢子,胚囊发育为蓼型。胚囊中卵细胞存在极性。助细胞在卵细胞产生极性分化前解体,即助细胞寿命较短。反足细胞在成熟胚囊中退化。极核在受精前融合,核中出现多个小核仁。 相似文献
20.
动物机体的大部分分化细胞具备全能性 ,成熟卵母细胞胞质中 m RNA、蛋白质等母型信息能使注入其中的细胞基因发生再程序化 ,从而启动新个体的发育。供体细胞和受体卵母细胞的周期和功能状态的同步协调是实现重构胚正常发育的关键。克隆动物的成功受供体细胞、受体卵母细胞以及二者之间的相互作用等多个因素的影响 ,其中的许多规律还未被掌握 ,动物克隆的研究必将揭示这些生物学规律 ,显示其巨大的科学意义 相似文献