Falchuk K H, Fawcett D W, Vallee B L
J Cell Sci. 1975 Jan;17(1):57-78. doi: 10.1242/jcs.17.1.57.
Euglena gracilis is a suitable model system to investigate the role of zinc in the process of cell division. In zinc-deficient organisms there is a characteristic arrest of cellular proliferation, the DNA content of the cells doubles, whereas RNA and protein contents decrease. The present investigations include the growth characteristics, changes in cellular morphology at various stages in the growth cycle, quantitation of zinc uptake and incorporation of tritium-labelled precursors into RNA by organisms grown in zinc sufficient (Zn+), (Zn2+ content 1 times 10-minus 5 M) or zinc-deficient (Zn minus), (Zn2+ content 1 times 10-7 M) medium. Cell division ceases on depletion of zinc from the medium. There are 20-fold less cells in (Zn minus) medium than in control cultures. The size of (Zn+) cells decreases during log phase due to a reduction in the paramylon content of the cytoplasm. The size of (Zn minus) cells, however, increases, due to an accumulation of paramylon. This results in a 13-fold increment in dry weight compared to control. Other cytoplasmic organelles, including Golgi bodies, mitochondria, etc. are normal. Nuclear morphology also is unchanged. There is a reduction in the rate of incorporation of labelled precursors into RNA by (Zn minus) cells. The DNA content of (Zn minus) E. gracilis, the absence of morphologic evidence to indicate that cell division has followed the doubling of the DNA, and the arrest in proliferation suggests that a critical zinc-dependent step in the cell cycle, localized to G2, is blocked in zinc deficiency.
纤细裸藻是研究锌在细胞分裂过程中作用的合适模型系统。在缺锌的生物体中，细胞增殖会出现特征性停滞，细胞的DNA含量翻倍，而RNA和蛋白质含量下降。目前的研究包括生长特性、生长周期不同阶段细胞形态的变化、锌摄取的定量以及在锌充足（Zn+，Zn2+含量为1×10−5 M）或缺锌（Zn−，Zn2+含量为1×10−7 M）培养基中生长的生物体将氚标记的前体掺入RNA的情况。当培养基中的锌耗尽时，细胞分裂停止。在（Zn−）培养基中的细胞数量比对照培养物中的少20倍。由于细胞质中副淀粉含量的减少，（Zn+）细胞在对数期的大小会减小。然而，（Zn−）细胞的大小会增加，这是由于副淀粉的积累。与对照相比，这导致干重增加了13倍。其他细胞质细胞器，包括高尔基体、线粒体等都是正常的。核形态也没有变化。（Zn−）细胞将标记前体掺入RNA的速率降低。（Zn−）纤细裸藻的DNA含量、缺乏表明细胞分裂跟随DNA加倍的形态学证据以及增殖停滞表明细胞周期中一个关键的锌依赖性步骤（定位于G2期）在缺锌时被阻断。
