Effects of mutagens on the clonal lifespan of Paramecium tetraurelia.
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.
Department of Hygiene, School of Medicine, Kinki University, Osakasayama, Japan.
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Fukushima
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Ogawa
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Sasagawa
D015112:4-Nitroquinoline-1-oxide / Q000494:pharmacology; D000818:Animals; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D009153:Mutagens / Q000494:pharmacology*; D016805:Paramecium tetraurelia / Q000187:drug effects*
D009153:Mutagens; D008769:Methylnitronitrosoguanidine; D015112:4-Nitroquinoline-1-oxide