title: Localized accumulation of tubulin during semi-open mitosis in the Caenorhabditis elegans embryo.
abstract: The assembly of microtubules inside the cell is controlled both spatially and temporally. During mitosis, microtubule assembly must be activated locally at the nascent spindle region for mitotic spindle assembly to occur efficiently. In this paper, we report that mitotic spindle components, such as free tubulin subunits, accumulated in the nascent spindle region, independent of spindle formation in the Caenorhabditis elegans embryo. This accumulation coincided with nuclear envelope permeabilization, suggesting that permeabilization might trigger the accumulation. When permeabilization was induced earlier by knockdown of lamin, tubulin also accumulated earlier. The boundaries of the region of accumulation coincided with the remnant nuclear envelope, which remains after nuclear envelope breakdown in cells that undergo semi-open mitosis, such as those of C. elegans. Ran, a small GTPase protein, was required for tubulin accumulation. Fluorescence recovery after photobleaching analysis revealed that the accumulation was accompanied by an increase in the immobile fraction of free tubulin inside the remnant nuclear envelope. We propose that this newly identified mechanism of accumulation of free tubulin-and probably of other molecules-at the nascent spindle region contributes to efficient assembly of the mitotic spindle in the C. elegans embryo.
authors.affiliation: Department of Genetics (Sokendai-Mishima), School of Life Science, Graduate University for Advanced Studies (Sokendai), Yata 1111, Mishima, Shizuoka 411-8540, Japan.
authors.forename: Hanako
authors.initials: H
authors.lastname: Hayashi
authors.forename: Kenji
authors.initials: K
authors.lastname: Kimura
authors.forename: Akatsuki
authors.initials: A
authors.lastname: Kimura
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology* / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D034882:Lamins / Q000235:genetics / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D009685:Nuclear Envelope / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000378:metabolism
chemical_list: D029742:Caenorhabditis elegans Proteins; D034882:Lamins; D014404:Tubulin; D020931:ran GTP-Binding Protein