Radioadaptive response of germ cells of male mice

Abstract

This study was aimed at estimating the damage to Synaptonemal Complex (SC) of male mice caused by radiation exposure at the ultimate premeiotic interphase. Four experimental groups were formed: group one was a group of unirradiated control, group two was the one received a low dose (50 mGy) of radiation, group three was the one received high dose (4 Gy) of radiation, and group four was first treated with low dose (50 mGy) and four hours later with a high dose of radiation (4 Gy). Mice were sacrificed four days after irradiation. Early pachytene cells were selected for the electron microscopic analysis of the SCs. These cells were supposed to be at premeiotic interphase at the time of irradiation. Treatment with low dose of radiation scarcely produced any substantial increase in aberration frequency of SC aberrations, while the exposure to high dose resulted in various types of damage. The group four demonstrated significantly lower frequencies of axial breaks or fragments than the group three did. At the same time, these two groups did not differ in the frequencies of inter- and intrachromosomal exchanges such as translocations, inversions, and deletions. It was supposed that the number of breaks produced by high dose of radiation was equal in the both groups. However a proportion of the states that remained unrepaired until pachytene and has expressed as gaps, fragments, and multiaxial configurations was reduced by pretreatment with the low dose of radiation.

本研究は、最終前減数間期に放射線照射を行なうことでひきおこされる、雄マウスの対合期複合体の損傷を測定することを目的としている。マウスは4実験群に分けた。第1群は非処理対照群、第2群は低線量(50mGy)放射線照射群、第3群は高線量(4Gy)放射線照射群、第4群は初めに低線量(50mGy)放射線を照射し、4時間後に高放射線量(4Gy)照射した群である。マウスは照射後4日目に処分した。早期パキテン期細胞を対合複合体の電子顕微鏡解析に選んだ。この細胞は照射時に前減数期であったと思われる。低線量放射線による処理は、対合期複合体の異常頻度をほとんど増強しないが、高線量にさらすと様々な種類の損傷をひきおこす。第4群は第3群に比べ、軸方向に沿った切断または断片が明かに少なかった。同時に転座、転位、欠失などの染色体間交換、染色体内交換の発生頻度は第3群と第4群とで差はなかった。高線量放射線照射により生じた切断数は、第3群と第4群で同じように思われる。しかしパキテン期まで修復されないままギャップ、断片、多軸立体配置として発現された状態の比率は、低放射線の前処理により低下した。