Laboratory of Cell Biology, Department of Life Science, College of Science, Research Information Center for Extremophile, Rikkyo University, Toshima, Tokyo 171-8501, Japan.
Protoplasma. 2010 May;241(1-4):63-74. doi: 10.1007/s00709-010-0107-y. Epub 2010 Feb 11.
To understand the cell cycle, we must understand not only mitotic division but also organelle division cycles. Plant and animal cells contain many organelles which divide randomly; therefore, it has been difficult to elucidate these organelle division cycles. We used the primitive red alga Cyanidioschyzon merolae, as it contains a single mitochondrion and plastid per cell, and organelle division can be highly synchronized by a light/dark cycle. We demonstrated that mitochondria and plastids multiplied by independent division cycles (organelle G1, S, G2 and M phases) and organelle division occurred before cell-nuclear division. Additionally, organelle division was found to be dependent on microtubules as well as cell-nuclear division. We have observed five stages of microtubule dynamics: (1) the microtubule disappears during the G1 phase; (2) alpha-tubulin is dispersed within the cytoplasm without forming microtubules during the S phase; (3) alpha-tubulin is assembled into spindle poles during the G2 phase; (4) polar microtubules are organized along the mitochondrion during prophase; and (5) mitotic spindles in cell nuclei are organized during the M phase. Microfluorometry demonstrated that the intensity peak of localization of alpha-tubulin changed in the order to spindle poles, mitochondria, spindle poles, and central spindle area, but total fluorescent intensity did not change remarkably throughout mitotic phases suggesting that division and separation of the cell nucleus and mitochondrion is mediated by spindle pole bodies. Inhibition of microtubule organization induced cell-nuclear division, mitochondria separation, and division of a single membrane-bound microbody, suggesting that similar to cell-nuclear division, mitochondrion separation and microbody division are dependent on microtubules.
为了理解细胞周期，我们不仅必须理解有丝分裂，还要理解细胞器分裂周期。植物和动物细胞含有许多随机分裂的细胞器；因此，阐明这些细胞器的分裂周期一直很困难。我们使用原始的红藻 Cyanidioschyzon merolae，因为它每个细胞含有一个线粒体和一个质体，并且细胞器的分裂可以通过光/暗周期高度同步。我们证明了线粒体和质体通过独立的分裂周期（细胞器 G1、S、G2 和 M 期）增殖，并且细胞器的分裂发生在核分裂之前。此外，细胞器的分裂被发现依赖于微管以及核分裂。我们观察到微管动力学的五个阶段：（1）在 G1 期微管消失；（2）在 S 期细胞质中 alpha-微管蛋白分散，不形成微管；（3）在 G2 期 alpha-微管蛋白组装成纺锤体极；（4）在前期沿着线粒体组织极性微管；（5）在 M 期组织细胞核中的有丝分裂纺锤体。微量荧光法证明 alpha-微管蛋白定位的强度峰值按纺锤体极、线粒体、纺锤体极和中央纺锤体区域的顺序变化，但在有丝分裂各期中总荧光强度没有明显变化，表明细胞核和线粒体的分裂和分离是由纺锤体极体介导的。微管组织的抑制诱导核分裂、线粒体分离和单个膜结合微体的分裂，表明类似于核分裂，线粒体分离和微体分裂依赖于微管。
