Corff S, Yuyama S
J Protozool. 1976 Nov;23(4):587-93. doi: 10.1111/j.1550-7408.1976.tb03847.x.
DNA synthesis during growth and differentiation in Naegleria gruberi strain NEG populations has been studied. Autoradiography of cells labeled with [3H]thymidine revealed that grains are concentrated over the nuclei in logarithmically growing populations of cells, whereas in differentiating cells, grains are scattered over the cytoplasm; i.e. no significant nuclear labeling is detectable. It was established by MAK chromatographic analysis that [3H]thymidine is incorporated into double-stranded DNA in Naegleria and that the actual amount of incorporation in the logarithmically growing populations of cells is 20 times greater than that in differentiating cells. These results suggest that nuclear DNA synthesis is reduced markedly soon after the initiation of differentiation, while cytoplasmic DNA synthesis continues. It was established from cell cycle analysis that the approximate intervals of G1, S, G2, and M phases were 180, 183, 90, and 28 min, respectively. Hence, the reduction in the nuclear DNA synthesis in differentiating cells is not due to the inhibition of initiation of DNA replication, but rather to the termination of the DNA replicating process. Thus DNA synthesis is curtailed in the presence of RNA and protein synthesis which are required for differentiation.
对格氏奈格里原虫NEG株群体生长和分化过程中的DNA合成进行了研究。用[3H]胸腺嘧啶核苷标记细胞的放射自显影显示，在对数生长期的细胞群体中，银粒集中在细胞核上，而在分化细胞中，银粒分散在细胞质中；即未检测到明显的细胞核标记。通过MAK色谱分析确定，[3H]胸腺嘧啶核苷被掺入格氏奈格里原虫的双链DNA中，并且在对数生长期的细胞群体中的实际掺入量比分化细胞中的高20倍。这些结果表明，分化开始后不久，细胞核DNA合成明显减少，而细胞质DNA合成仍在继续。通过细胞周期分析确定，G1、S、G2和M期的大致间隔分别为180、183、90和28分钟。因此，分化细胞中细胞核DNA合成的减少不是由于DNA复制起始的抑制，而是由于DNA复制过程的终止。因此，在分化所需的RNA和蛋白质合成存在的情况下，DNA合成受到抑制。
