Analysis of radioresistant factors in cultured Mongolian gerbil cells

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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.