Department of Biological Sciences, California State University, 1250 Bellflower Boulevard, Long Beach, California 90840 USA.
Mycologia. 2010 May-Jun;102(3):493-512. doi: 10.3852/09-193.
Ustilago maydis is a basidiomycete fungus that exhibits a yeast-like and a filamentous form. Growth of the fungus in the host leads to additional morphological transitions. The different morphologies are characterized by distinct nuclear movements. Dynein and alpha-tubulin are required for nuclear movements and for cell morphogenesis of the yeast-like form. Lis1 is a microtubule plus-end tracking protein (+TIPs) conserved in eukaryotes and required for nuclear migration and spindle positioning. Defects in nuclear migration result in altered cell fate and aberrant development in metazoans, slow growth in fungi and disease in humans (e.g. lissencephaly). Here we investigate the role of the human LIS1 homolog in U. maydis and demonstrate that it is essential for cell viability, not previously seen in other fungi. With a conditional null mutation we show that lis1 is necessary for nuclear migration in the yeast-like cell and during the dimorphic transition. Studies of asynchronous exponentially growing cells and time-lapse microscopy uncovered novel functions of lis1: It is necessary for cell morphogenesis, positioning of the septum and cell wall integrity. lis1-depleted cells exhibit altered axes of growth and loss of cell polarity leading to grossly aberrant cells with clusters of nuclei and morphologically altered buds devoid of nuclei. Altered septum positioning and cell wall deposition contribute to the aberrant morphology. lis1-depleted cells lyse, indicative of altered cell wall properties or composition. We also demonstrate, with indirect immunofluorescence to visualize tubulin, that lis1 is necessary for the normal organization of the microtubule cytoskeleton: lis1-depleted cells contain more and longer microtubules that can form coils perpendicular to the long axis of the cell. We propose that lis1 controls microtubule dynamics and thus the regulated delivery of vesicles to growth sites and other cell domains that govern nuclear movements.
玉米黑粉菌是一种担子菌真菌，具有酵母状和丝状两种形态。真菌在宿主中的生长导致了额外的形态转变。不同的形态特征表现出明显不同的核运动。动力蛋白和α-微管蛋白对于酵母状形态的核运动和细胞形态发生是必需的。Lis1 是一种在真核生物中保守的微管末端追踪蛋白（+TIPs），对于核迁移和纺锤体定位是必需的。核迁移缺陷会导致后生动物的细胞命运改变和发育异常、真菌生长缓慢以及人类疾病（例如无脑回畸形）。在这里，我们研究了人 LIS1 同源物在玉米黑粉菌中的作用，并证明它对于细胞活力是必需的，这在其他真菌中尚未见报道。通过条件性缺失突变，我们表明 lis1 对于酵母状细胞中的核迁移以及二态性转变是必需的。对异步指数生长细胞和延时显微镜的研究揭示了 lis1 的新功能：它对于细胞形态发生、隔膜的定位和细胞壁完整性是必需的。lis1 缺失细胞表现出生长轴的改变和细胞极性的丧失，导致具有核簇的明显异常细胞和形态改变的芽，其中没有核。隔膜定位和细胞壁沉积的改变导致了形态异常。lis1 缺失细胞裂解，表明细胞壁性质或组成发生了改变。我们还通过间接免疫荧光来可视化微管，证明了 lis1 对于微管细胞骨架的正常组织是必需的：lis1 缺失细胞含有更多和更长的微管，可以形成与细胞长轴垂直的线圈。我们提出，lis1 控制微管动力学，从而控制囊泡向生长部位和其他控制核运动的细胞区域的有调节的输送。
