Genetic effects of HZE and cosmic radiation

HZE(高エネルギー重荷電粒子)および宇宙放射線の遺伝的影響を調べるため、ショウジョウバエ(Drosophila melanogaster)の成虫雄と幼虫をスペースシャトル/エンデバー号(STS-47)に搭載し、雄の生殖細胞(精子やその元となる精原細胞など)に起こる伴性劣性致死突然変異と、幼虫の翅原基体細胞に起こる染色体のつなぎかえによる突然変異を調べた。用いた系統は、標準的な野生株(Canton-S)と放射線高感受性株(mei-41)である。各系統で、成虫雄は200匹ずつ、幼虫は約6000匹ずつを搭載し宇宙環境に曝すとともに、ほぼ同数を地上対照群として、宇宙飛行群と同じ環境条件(温度と湿度)で飼育した。宇宙飛行は約8日間であった。帰還した雄のハエは、伴性劣性致死突然変異を調べるため、検出用系統の処女雌に交配し、次々世代で致死遺伝子を保有しているX染色体を検出した。宇宙飛行群の致死遺伝子をもった染色体頻度は、地上対照群の頻度に比べて、野生株では2倍、放射線高感受性株では3倍高かった。幼虫は、帰還時にほとんどが蛹になっており、翌日より徐々に羽化が始まった。羽化した成虫は、順次70%アルコールで貯蔵し、後に翅標本を作成して、染色体突然変異由来の翅毛変異スポットを調べた。野生株では、宇宙飛行群と地上対照群の頻度は、ほぼ同じであった。放射線高感受性株から分離してくるMuller-5個体における頻度は、地上対照群に比べて宇宙飛行群では、1.5倍高かった。しかし、放射線高感受性個体における宇宙飛行群の頻度は、地上対照群に比べて有意に低い頻度を示した。地上対照群に比べて、宇宙飛行群の劣性致死突然変異の高頻度は、生殖細胞において、放射線と微小重力の突然変異誘発作用への相乗効果を示唆している。しかし、この相乗効果は、体細胞の染色体突然変異誘発作用に対しては観察されなかった。
For examining the genetic effects of High Energy Heavy ions (HZE) and cosmic radiation, adult males and larvae of fruit flies (Drosophila melanogaster) were loaded on the Space Shuttle, Endeavor (STS-47), and sex-linked recessive lethal mutation in the male germ cells (spermatozoa and spermatogonia that produce them) and chromosome-recombination-derived mutation on the larva wing basal somatic cells were investigated. The strains used were a standard wild type strain (Canton-S) and a radiation sensitive strain (mei-41). Two-hundred adult males and about 6000 larvae of each strain were loaded and exposed to the cosmic environment. At the same time, almost the same number of adult flies and larvae were bred in the same environmental condition (temperature and humidity) as ground control groups. The flight period was about eight days. The returned male flies were mated with virgin female flies from a detection strain for investigating sex-linked recessive lethal mutation. X chromosomes with lethal genes were detected on the second generation. In the returned flies, the frequency of chromosomes with lethal genes was two times higher in the wild type strain and three times higher in the radiation sensitive strain than that of the ground control groups. Most of the returned larvae were in the pupal stage on the return day, and began to emerge on the next day. The emerged adult flies were stored in 70 percent alcohol solutions, and their wing samples were prepared for investigating the wing mutation spots derived from chromosome mutation. Mutation frequency in the wild type strain was almost the same between the flight and ground groups. The frequency in the Muller-5 individuals separated from the radiation sensitive strain was one and half times higher in the flight group than in the ground control group. However, the frequency in the radiation sensitive strain was significantly lower in the flight group than the ground group. The higher recessive lethal mutation frequency in the flight group suggests the synergistic effect of radiation and minute gravity on mutation induction in germ cells. However, this synergy effect was not observed on the chromosome mutation induction in somatic cells.
資料番号: AA0004115012
レポート番号: NASDA-TMR-940002 V.1