Regulation of microtubule organization during interphase and M phase.
Microtubule (MT) dynamics and organization change markedly during interphase-M phase transition of the cell cycle. This mini review focuses first on p220, a ubiquitous MT-associated protein of Xenopus. p220 is phosphorylated by p34cdc2 kinase and MAP kinase in M phase, and concomitantly loses its MT-binding and MT-stabilizing activities. A cDNA encoding p220 was cloned, which identified p220 as a Xenopus homolog of MAP4, and p220 was therefore termed XMAP4. To examine the physiological relevance of XMAP4 phosphorylation during mitosis, Xenopus A6 cells were transfected with cDNA encoding wild-type or various XMAP4 mutants fused with a green fluorescent protein (GFP). Mutations of serine and threonine within potential phosphorylation sites for p34cdc2 kinase to nonphosphorylatable alanine interfered with mitosis-associated reduction in MT-affinity of XMAP4 and their overexpression affected chromosome movement during anaphase A. These results indicated that phosphorylation of XMAP4 by p34cdc2 kinase is responsible for the decrease in its MT-binding and MT-stabilizing activities during mitosis which are important for chromosome movement during anaphase A. The second focus is on a novel monoclonal antibody W8C3, which recognizes alpha-tubulin. W8C3 stained spindle MTs but not interphase MTs of Xenopus A6 cells, although tubulin dimers in M phase and interphase were equally recognized by this antibody. The difference in MT staining pattern may be because the W8C3-recognition site on alpha-tubulin is sterically hidden in interphase MTs but not in spindle MTs.
Shiina
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Tsukita Cell Axis Project, ERATO, Japan Science and Technology Corporation, Kyoto Research Park, Shimogyo-ku, Kyoto 600-8813, Japan.
Tsukita
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S
D000705:Anaphase / Q000502:physiology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000276:immunology; D002460:Cell Line; D002875:Chromosomes / Q000378:metabolism; D049452:Green Fluorescent Proteins; D007211:Indoles / Q000737:chemistry; D007399:Interphase / Q000502:physiology*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008858:Microscopy, Phase-Contrast; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014404:Tubulin / Q000276:immunology; D014981:Xenopus; D029867:Xenopus Proteins / Q000235:genetics / Q000502:physiology*
D000911:Antibodies, Monoclonal; D018797:Cell Cycle Proteins; D007211:Indoles; D008164:Luminescent Proteins; C403415:MAP230 protein, Xenopus; D008869:Microtubule-Associated Proteins; C490113:PCM1 protein, Xenopus; D011993:Recombinant Fusion Proteins; D014404:Tubulin; D029867:Xenopus Proteins; D049452:Green Fluorescent Proteins; C007293:DAPI; D016203:CDC2 Protein Kinase