Ishikawa T, Sakurai J, Takayama S
Basic Life Sci. 1985;35:297-313. doi: 10.1007/978-1-4899-2218-2_19.
Since the capacity for DNA repair relative to other cellular processes should be an important parameter of mutagenesis, carcinogenesis, and also aging, this capacity should preferably be studied in intact animals. Thus, we developed autoradiographic techniques for measuring DNA repair directly in vivo. By these methods unscheduled DNA synthesis (UDS) was detected quantitatively as silver grains on epithelial cells of mouse skin after treatment with chemical carcinogens or UV irradiation, and on cerebral ganglion cells of aquarium fish after treatment with various chemical carcinogens. Several interesting findings so far obtained are presented. Possible age-related change in the UDS response was examined by the skin technique with mice of 2 and 18 months old. Similar dose-dependent induction of UDS was observed in mice of both ages after treatment with 4-hydroxyaminoquinoline 1-oxide; their levels of UDS at each dose were not significantly different. The dose-response curves for young and aged animals after UV irradiation showed similar increases to a plateau at low doses, but their responses to high doses were very different: in aged mice the UDS level decreased markedly with increase in the dose, whereas in young mice it remained at the same level. This suggests that in aged animals, high doses of UV irradiation cause deterioration of DNA repair systems, and that aged animals cannot repair extensive DNA damage efficiently. It is generally thought that DNA has a stable structure and a much slower turnover than other cellular components. Although the effect of DNA repair on DNA turnover may be insignificant, accumulation of repaired DNA in cells should result in detectable DNA turnover. Therefore, we investigated DNA turnover in postmitotic ganglion cells of rat retina. However, careful autoradiographic studies on pairs of eyes showed no detectable DNA turnover up to nearly their median life span (2 years). This result suggests that the DNA of post-mitotic cells, which are not replaced throughout the life span of the animal, is very stable and is possibly protected in some special way.
由于相对于其他细胞过程的DNA修复能力应该是诱变、致癌以及衰老的一个重要参数，因此最好在完整的动物体内研究这种能力。于是，我们开发了用于直接在体内测量DNA修复的放射自显影技术。通过这些方法，在用化学致癌物或紫外线照射后，在小鼠皮肤的上皮细胞上以及在用各种化学致癌物处理后的水族馆鱼类的脑神经节细胞上，将非预定DNA合成（UDS）定量检测为银颗粒。本文呈现了目前获得的一些有趣发现。我们用皮肤技术对2个月和18个月大的小鼠进行研究，以检查UDS反应中可能与年龄相关的变化。在用4-羟基氨基喹啉1-氧化物处理后，在两个年龄段的小鼠中均观察到了类似的剂量依赖性UDS诱导；各剂量下它们的UDS水平没有显著差异。紫外线照射后年轻和年老动物的剂量反应曲线在低剂量时显示出类似的增加至平稳期，但它们对高剂量的反应非常不同：在老年小鼠中，UDS水平随着剂量增加而显著下降，而在年轻小鼠中它保持在相同水平。这表明在老年动物中，高剂量的紫外线照射会导致DNA修复系统的恶化，并且老年动物不能有效地修复广泛的DNA损伤。一般认为DNA具有稳定的结构，并且其周转比其他细胞成分慢得多。虽然DNA修复对DNA周转的影响可能微不足道，但细胞中修复后的DNA积累应该会导致可检测到的DNA周转。因此，我们研究了大鼠视网膜有丝分裂后神经节细胞中的DNA周转。然而，对成对眼睛进行的仔细放射自显影研究表明，直到接近它们的平均寿命（2年）都没有检测到DNA周转。这一结果表明，在动物整个寿命期内都不会被替换的有丝分裂后细胞的DNA非常稳定，并且可能以某种特殊方式受到保护。
