Analysis of radioresistant factors in cultured Mongolian gerbil cells

蒙古沙鼠(长爪沙鼠)是已知的抗辐射能力最强的动物之一。为了分析这种动物的高辐射抗性的机制，我们检测了来自蒙古沙土鼠胚胎的正常二倍体细胞和来自不同哺乳动物的培养的胚胎细胞的X射线敏感性。蒙古沙土鼠细胞的X射线剂量存活曲线测得的D0值为2.1~2.3Gy值，是人细胞D0值的两倍。在2GyX射线照射下，人细胞有丝分裂延迟时间是蒙古沙土鼠细胞的3倍。此外，在这种X射线下，在人类细胞中检测到的染色体畸变率是蒙古沙鼠细胞的十倍，而其他啮齿动物细胞的频率介于两种细胞株的值之间。在连续传代培养过程中，在第30代和第60代用X射线照射细胞时，X射线-剂量存活曲线也观察到类似的宽幅变化。有趣的是，蒙古沙土鼠细胞也表现出对紫外线(UV)的高抗性，但这些细胞株的紫外线敏感性与其DNA修复能力之间没有相关性。用脉冲场电泳法测定了蒙古沙鼠细胞与其他哺乳动物细胞的DNA双链断裂(DNA DBS)及其修复动力学。然而，在不同的哺乳动物细胞株中观察到了一致的DNA DBS重新连接的动力学。这些数据表明，蒙古沙土鼠细胞的辐射抗性与它们的基因序列有关，它们的辐射抗性因子可能是一些共同的分子，不仅与电离辐射有关，还与紫外线或化学物质有关，而不是修复酶对特定DNA损伤的作用。

The Mongolian gerbil (Meriones unguiculatus) is known to be one of the most radioresistant animals. In order to analyze the mechanism of high radioresistance in this animal, we have examined the X-ray sensitivity of normal diploid cells from Mongolian gerbil embryos compared with those of cultured embryo cells obtained from different mammalian species. The D0 value determined from X-ray-does survival curves for Mongolian gerbil cells ranged from 2.1 to 2.3 Gy, values which are twice as high as those for human cells. When cells were irradiated with 2 Gy of X-rays, three times longer mitotic delay was observed in human cells than in Mongolian gerbil cells. At this X-ray does, furthermore, ten times more chromosome aberrations were detected in human cells than in Mongolian gerbil cells, and frequencies of other rodent cells lay between the values for the two cell strains. Similar wide variations were observed in X-ray-does survival curves when the cell were irradiated with X-ray at passage 30 and 60 on successive transfer in culture. Interestingly, the Mongolian gerbil cells also showed a high resistance to ultraviolet light (UV), but there was no correlation between UV sensitivity of these cell strains and their DNA repair abilities. Using a pulse-field electrophoresis technique, we measured X-ray induced DNA double-strand breaks (DNA dbs) and their repair kinetics in Mongolian gerbil cells compared with those in other mammalian cells. However, a consistent kinetics of DNA dbs rejoining was observed among various mammalian cell strains. These data indicate that the radioresistance of Mongolian gerbil cells is associated with their genetic trains, and that their radioresistant factors may be some common molecules responsible to not only ionizing radiations but also UV or chemicals, rather than repair enzymes against specific DNA damages.