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

The University of Tokushima, Tokusima, Tokushima, 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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    • "By visualizing pericentrin, a major centrosomal protein, Can et al. (2005) demonstrated a dispersion of pericentriolar material in BPA-treated mouse oocytes, that resulted in increased number of centrosomes and multipolar spindles. On the other hand, in dividing cells of angiosperms and gymnosperms , which lack centrosomes, mitotic MTs are considered to be nucleated at pleiomorphic MTOCs, as evidenced by the transposable localization of g-tubulin, an integral component of MTOCs, at different places where the specialized plant MT arrays are organized (Murata et al., 2005; Binarov a et al., 2006; Brown and Lemmon, 2007). Although gymnosperms develop acentriolar spindles as well, several studies have shown that they display special centrosomal properties (Wang et al., 1991; Fowke, 1993; Zachariadis et al., 2004 ). "
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    ABSTRACT: The effects of bisphenol A (BPA), an endocrine chemical disruptor extensively used in the plastic and epoxy resin industry, on dividing root tip cells of the gymnosperm Abies cephalonica Loudon were investigated by confocal laser scanning microscopy after tubulin and endoplasmic reticulum immuno- localization and DNA staining. Microtubule arrays of all mitotic stages were disrupted within a few hours of treatment: preprophase bands exhibited asymmetric width; prometaphase, metaphase and anaphase spindles appeared sharply pointed, sigmoid or multipolar; phragmoplast microtubules were elongated and occasionally bended toward the daughter nuclei. Depending on the mitotic stage, the chromosomes appeared condensed at prophase, as a compact mass at metaphase and anaphase, unsegregated or bridged at telophase. Endoplasmic reticulum patterns were also affected, reflecting those of the respective microtubule arrays. Recovery of the microtubules after oryzalin treatment was more effective in a BPA solution than in water. It is concluded that the plant mitotic apparatus microtubules are very sensitive to BPA, the effect of which depends on the specific cell cycle stage. The formation of multipolar spindles is reminiscent of animal cells and is ascribed to the induction of multiple microtubule nucle- ation sites, deriving from the centrosomal properties of gymnosperms.
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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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    • "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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