Banuett Flora, Herskowitz Ira
Department of Biochemistry and Biophysics, School of Medicine, University of California-San Francisco, 513 Parnassus Ave, San Francisco, CA 94143-0448, USA.
Fungal Genet Biol. 2002 Nov;37(2):149-70. doi: 10.1016/s1087-1845(02)00548-0.
Ustilago maydis is a dimorphic Basidiomycete fungus with a yeast-like form and a hyphal form. Here we present a comprehensive analysis of bud formation and the actin and microtubule cytoskeletons of the yeast-like form during the cell cycle. We show that bud morphogenesis entails a series of shape changes, initially a tubular or conical structure, culminating in a cigar-shaped cell connected to the mother cell by a narrow neck. Labelling of cells with concanavalin A demonstrated that growth occurs at bud tip. Indirect immunofluorescence studies revealed that the actin cytoskeleton consists of patches and cables that polarize to the presumptive bud site and the bud tip and an actin ring that forms at the neck region. Because the bud tip corresponds to the site of active cell wall growth, we hypothesize that actin is involved in secretion of cell wall components. The microtubule cytoskeleton has recently been shown to consist of a cytoplasmic network during interphase that disassembles at mitosis when a spindle and astral microtubules are formed. We have carried out studies of U. maydis cells synchronized by the microtubule-depolymerizing drug thiabendazole which allow us to construct a temporal sequence of steps in spindle formation and spindle elongation during the cell cycle. These studies suggest that astral microtubules may be involved in early stages of spindle orientation and migration of the nucleus into the bud and that the spindle pole bodies may be involved in reestablishment of the cytoplasmic microtubule network.
玉蜀黍黑粉菌是一种二态担子菌真菌，具有酵母样形态和菌丝形态。在此，我们对酵母样形态在细胞周期中的出芽形成以及肌动蛋白和微管细胞骨架进行了全面分析。我们表明，芽形态发生需要一系列形状变化，最初是管状或圆锥形结构，最终形成通过狭窄颈部与母细胞相连的雪茄形细胞。用伴刀豆球蛋白A标记细胞表明生长发生在芽尖。间接免疫荧光研究表明，肌动蛋白细胞骨架由斑块和纤维束组成，它们极化到假定的芽位点和芽尖，以及在颈部区域形成的肌动蛋白环。由于芽尖对应于活跃细胞壁生长的位点，我们推测肌动蛋白参与细胞壁成分的分泌。最近的研究表明，微管细胞骨架在间期由细胞质网络组成，在有丝分裂时当纺锤体和星体微管形成时会解体。我们对用微管解聚药物噻苯达唑同步化的玉蜀黍黑粉菌细胞进行了研究，这使我们能够构建细胞周期中纺锤体形成和纺锤体伸长步骤的时间序列。这些研究表明，星体微管可能参与纺锤体定向和细胞核向芽迁移的早期阶段，并且纺锤极体可能参与细胞质微管网络的重建。
