Fukushima S, Ogawa H, Sasagawa S
Department of Hygiene, School of Medicine, Kinki University, Osakasayama, Japan.
Mutat Res. 1992 Jan;275(1):41-6. doi: 10.1016/0921-8734(92)90007-c.
There has been interest in the phenomenon that a cell cannot undergo unlimited reproduction under adequate conditions and undergoes senescence. In holotrichous ciliates, Paramecium has a limit of vegetative reproduction without sexual reproduction but Tetrahymena does not always have a limited lifespan. Comparing the two species would increase our knowledge of the mechanism of cellular clonal aging. We previously showed that mutations induced by X-rays shorten clonal lifespan. In this study, we examined whether mutagens shorten the clonal lifespan of Paramecium tetraurelia. P. tetraurelia was exposed to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 0.045 mg/ml, for 30 min. The animal was exposed to MNNG 6 times in total while young (under 80 divisions from the start of a clonal life cycle) or 4 times during the senescent stage. MNNG shortened the clonal lifespan as expressed by the decrease in fission number from 186 +/- 55 (4 cell lines) to 136 +/- 21 (6 cell lines) with the first two treatments but with further exposures the lifespan increased to 182 +/- 15 (5 cell lines). MNNG had no effect when administered at the older age. Exposure of P. tetraurelia to 4-nitroquinoline-N-oxide at 0.021 mg/ml twice for 12 and 15 min at the younger age reduced the mean clonal lifespan from 143 +/- 28 to 125 +/- 21 and the maximum lifespan from 263 +/- 33 to 175 +/- 25.
细胞在适宜条件下无法进行无限繁殖并会衰老，人们一直对这一现象感兴趣。在全毛目纤毛虫中，草履虫在无性繁殖时存在营养繁殖的极限，而四膜虫的寿命并不总是有限的。比较这两个物种将增加我们对细胞克隆衰老机制的了解。我们之前表明，X射线诱导的突变会缩短克隆寿命。在本研究中，我们研究了诱变剂是否会缩短四膜虫的克隆寿命。将四膜虫暴露于0.045 mg/ml的烷基化剂N-甲基-N'-硝基-N-亚硝基胍（MNNG）中30分钟。该动物在幼年期（从克隆生命周期开始起少于80次分裂）总共暴露于MNNG 6次，或在衰老期暴露4次。如通过裂变数的减少所表示的，MNNG缩短了克隆寿命，前两次处理时从186±55（4个细胞系）降至136±21（6个细胞系），但随着进一步暴露，寿命增加到182±15（5个细胞系）。在老年期给予MNNG没有效果。在幼年期将四膜虫暴露于0.021 mg/ml的4-硝基喹啉-N-氧化物中两次，每次12分钟和15分钟，平均克隆寿命从143±28降至125±21，最大寿命从263±33降至175±25。
