Straube Anne, Brill Marianne, Oakley Berl R, Horio Tetsuya, Steinberg Gero
Max-Planck-Institut für Terrestrische Mikrobiologie, Karl-von-Frisch-Strabetae, D-35043 Marburg, Germany.
Mol Biol Cell. 2003 Feb;14(2):642-57. doi: 10.1091/mbc.e02-08-0513.
Growth of most eukaryotic cells requires directed transport along microtubules (MTs) that are nucleated at nuclear-associated microtubule organizing centers (MTOCs), such as the centrosome and the fungal spindle pole body (SPB). Herein, we show that the pathogenic fungus Ustilago maydis uses different MT nucleation sites to rearrange MTs during the cell cycle. In vivo observation of green fluorescent protein-MTs and MT plus-ends, tagged by a fluorescent EB1 homologue, provided evidence for antipolar MT orientation and dispersed cytoplasmic MT nucleating centers in unbudded cells. On budding gamma-tubulin containing MTOCs formed at the bud neck, and MTs reorganized with >85% of all minus-ends being focused toward the growth region. Experimentally induced lateral budding resulted in MTs that curved out of the bud, again supporting the notion that polar growth requires polar MT nucleation. Depletion or overexpression of Tub2, the gamma-tubulin from U. maydis, affected MT number in interphase cells. The SPB was inactive in G2 phase but continuously recruited gamma-tubulin until it started to nucleate mitotic MTs. Taken together, our data suggest that MT reorganization in U. maydis depends on cell cycle-specific nucleation at dispersed cytoplasmic sites, at a polar MTOC and the SPB.
大多数真核细胞的生长需要沿着微管（MTs）进行定向运输，这些微管在与核相关的微管组织中心（MTOCs）处成核，如中心体和真菌纺锤体极体（SPB）。在此，我们表明致病真菌玉米黑粉菌在细胞周期中利用不同的微管成核位点来重新排列微管。对绿色荧光蛋白标记的微管和由荧光EB1同源物标记的微管正端进行体内观察，为未出芽细胞中微管的反极取向和分散的细胞质微管成核中心提供了证据。在出芽时，含γ-微管蛋白的微管组织中心在芽颈处形成，微管重新组织，超过85%的负端朝向生长区域。实验诱导的侧向出芽导致微管从芽中弯曲出来，再次支持了极性生长需要极性微管成核的观点。玉米黑粉菌的γ-微管蛋白Tub2的缺失或过表达影响了间期细胞中的微管数量。纺锤体极体在G2期不活跃，但持续招募γ-微管蛋白，直到它开始形成有丝分裂微管。综上所述，我们的数据表明玉米黑粉菌中的微管重组取决于在分散的细胞质位点、极性微管组织中心和纺锤体极体处的细胞周期特异性成核。
