Murata, T. et al. Microtubule-dependent microtubule nucleation based on recruitment of -tubulin in higher plants. Nature Cell Biol. 7, 961-968

National Institute for Basic Biology, Okazaki 444-8585, Japan.
Nature Cell Biology (Impact Factor: 19.68). 11/2005; 7(10):961-8. DOI: 10.1038/ncb1306
Source: PubMed


Despite the absence of a conspicuous microtubule-organizing centre, microtubules in plant cells at interphase are present in the cell cortex as a well oriented array. A recent report suggests that microtubule nucleation sites for the array are capable of associating with and dissociating from the cortex. Here, we show that nucleation requires extant cortical microtubules, onto which cytosolic gamma-tubulin is recruited. In both living cells and the cell-free system, microtubules are nucleated as branches on the extant cortical microtubules. The branch points contain gamma-tubulin, which is abundant in the cytoplasm, and microtubule nucleation in the cell-free system is prevented by inhibiting gamma-tubulin function with a specific antibody. When isolated plasma membrane with microtubules is exposed to purified neuro-tubulin, no microtubules are nucleated. However, when the membrane is exposed to a cytosolic extract, gamma-tubulin binds microtubules on the membrane, and after a subsequent incubation in neuro-tubulin, microtubules are nucleated on the pre-existing microtubules. We propose that a cytoplasmic gamma-tubulin complex shuttles between the cytoplasm and the side of a cortical microtubule, and has nucleation activity only when bound to the microtubule.

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    • "Similarly MTOC-independent nucleation of cytoplasmic microtubules occurs in many phyla. Murata et al. (2005) showed convincingly that cortical microtubules in higher plant cells are nucleated from the sides of existing microtubules at a characteristic angle of 42º with respect to existing microtubules, that γ-tubulin is at the branch points, and that lateral microtubule nucleation is γ-tubulin dependent. Similarly, Janson et al. (2005) demonstrated that microtubules are nucleated from γ-tubulin complexes at the sides of cytoplasmic microtubules in S. pombe. "
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    ABSTRACT: Tremendous progress has been made in understanding the functions of γ-tubulin and, in particular, its role in microtubule nucleation since the publication of its discovery in 1989. The structure of γ-tubulin has been determined, and the components of γ-tubulin complexes have been identified. Significant progress in understanding the structure of the γ-tubulin ring complex and its components has led to a persuasive model for how these complexes nucleate microtubule assembly. At the same time, data have accumulated that γ-tubulin has important but less well understood functions that are not simply a consequence of its function in microtubule nucleation. These include roles in the regulation of plus-end microtubule dynamics, gene regulation, and mitotic and cell cycle regulation. Finally, evidence is emerging that γ-tubulin mutations or alterations of γ-tubulin expression play an important role in certain types of cancer and in other diseases. © 2015 Oakley et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (
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    • "Cortical microtubules are nucleated from g-tubulin complexes localized at other microtubules or at the plasma membrane (e.g. Murata et al. 2005, Nakamura et al. 2010). Therefore, branches or ends of microtubules are likely to indicate the position of a nucleating complex. "
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    ABSTRACT: Charasomes are convoluted plasma membrane domains in the green alga Chara australis. They harbour H(+)-ATPases involved in acidification of the medium which facilitates carbon uptake required for photosynthesis. In this study we investigated the distribution of cortical microtubules and cortical actin filaments in relation to the distribution of charasomes. We found that microtubules and actin filaments were largely lacking beneath the charasomes suggesting the absence of nucleating and/or anchoring complexes or an inhibitory effect on polymerization. We also investigated the influence of cytoskeleton inhibitors on the light-dependent growth and the darkness-induced degradation of charasomes. Inhibition of cytoplasmic streaming by cytochalasin D significantly inhibited charasome growth and delayed charasome degradation whereas depolymerization of microtubules by oryzalin or stabilization of microtubules by paclitaxel had no effect. Our data indicate that the membrane at the cytoplasmic surface of charasomes has different properties in comparison with the smooth plasma membrane. We show further that the actin cytoskeleton is necessary for charasome growth and facilitates charasome degradation presumably via trafficking of secretory and endocytic vesicles, respectively. However, microtubules are neither required for charasome growth nor for charasome degradation. © The Author(s) 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.
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    • "entro - some . Microtubules also moved outward by dynein - powered sliding , but sliding was not es - sential for aster growth . How microtubules are nucleated away from the centrosome in inter - phase asters is not clear . A logical possibility is that microtubules are nucleated from the sides of preexisting microtubules , as they are in plants ( Murata et al . 2005 ) , via recruitment of g - tubu - lin complexes by Augmin / Haus complexes ( Petry et al . 2013 ) . However , in preliminary ex - periments , immunodepletion of augmin did not block aster growth ( K Ishihara and TJ Mitch - ison , unpubl . ) . We concluded that interphase asters in large egg and blastomere cells likely grow outward as an"
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    ABSTRACT: The first 12 cleavage divisions in Xenopus embryos provide a natural experiment in size scaling, as cell radius decreases ∼16-fold with little change in biochemistry. Analyzing both natural cleavage and egg extract partitioned into droplets revealed that mitotic spindle size scales with cell size, with an upper limit in very large cells. We discuss spindle-size scaling in the small- and large-cell regimes with a focus on the "limiting-component" hypotheses. Zygotes and early blastomeres show a scaling mismatch between spindle and cell size. This problem is solved, we argue, by interphase asters that act to position the spindle and transport chromosomes to the center of daughter cells. These tasks are executed by the spindle in smaller cells. We end by discussing possible mechanisms that limit mitotic aster size and promote interphase aster growth to cell-spanning dimensions. Copyright © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
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