Smith M G, Simon V R, O'Sullivan H, Pon L A
Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Mol Biol Cell. 1995 Oct;6(10):1381-96. doi: 10.1091/mbc.6.10.1381.
During early stages of meiosis I, yeast mitochondria fuse to form a single continuous thread. Thereafter, portions of the mitochondrial thread are equally distributed to daughter cells. Using time-lapse fluorescence microscopy and a membrane potential sensing dye, mitochondria are resolved as small particles at the cell periphery in pre-meiotic, living yeast. These organelles display low levels of movement. During meiosis I, we observed a threefold increase in mitochondrial motility. Mitochondrial movements were linear, occurred at a maximum velocity of 25 +/- 6.7 nm/s, and resulted in organelle collision and fusion to form elongated tubular structures. Mitochondria do not co-localize with microtubules. Destabilization of microtubules by nocodazole treatment has no significant effect on the rate and extent of thread formation. In contrast, yeast bearing temperature-sensitive mutations in the actin-encoding ACT1 gene (act1-3 and act1-133) exhibit abnormal mitochondrial aggregation, fragmentation, and enlargement as well as loss of mitochondrial motility. In act1-3 cells, mitochondrial defects and actin delocalization occur only at restrictive temperatures. The act1-133 mutation, which perturbs the myosin-binding site of actin without significantly affecting actin cytoskeletal structure in meiotic yeast, results in mitochondrial morphology and motility defects at restrictive and permissive temperatures. These studies support a role for the actin cytoskeleton in the control of mitochondrial position and movements in meiotic yeast.
在减数分裂I的早期阶段，酵母线粒体融合形成一条单一的连续细丝。此后，线粒体细丝的部分会平均分配到子细胞中。利用延时荧光显微镜和一种膜电位传感染料，在减数分裂前的活酵母中，线粒体在细胞周边被解析为小颗粒。这些细胞器的运动水平较低。在减数分裂I期间，我们观察到线粒体的运动性增加了两倍。线粒体的运动是线性的，最大速度为25±6.7 nm/s，导致细胞器碰撞和融合形成细长的管状结构。线粒体不与微管共定位。用诺考达唑处理使微管不稳定，对细丝形成的速率和程度没有显著影响。相反，在编码肌动蛋白的ACT1基因中携带温度敏感突变的酵母（act1-3和act1-133）表现出线粒体异常聚集、碎片化和增大，以及线粒体运动性丧失。在act1-3细胞中，线粒体缺陷和肌动蛋白的错位仅在限制温度下发生。act1-133突变扰乱了肌动蛋白的肌球蛋白结合位点，而在减数分裂酵母中对肌动蛋白细胞骨架结构没有显著影响，在限制温度和允许温度下都会导致线粒体形态和运动性缺陷。这些研究支持了肌动蛋白细胞骨架在减数分裂酵母中线粒体位置和运动控制中的作用。
