Tergite anormality induced by ultraviolet light in Drodophila melanogaster

研究化学物质、电离辐射和紫外光诱发的异常的一个重要问题是如何确定阈值（安全剂量）作为剂量的函数。在果蝇中，从胚胎期开始在普通琼脂培养基中生长的1龄幼虫在UVC照射后，在标准培养基中培养直到成虫。首次发现在发育成人中出现高频率的赤铁矿异常。探讨了阈值的存在，幼虫的致死机理及异常现象。幼虫存活率定义为受辐照幼虫数与发育成虫数之比，赤霉病发生频率定义为赤霉病成虫数与存活成虫总数之比。以切除修复缺陷型和CPD光解酶缺陷型突变菌株为研究对象，发现引起幼虫死亡和赤霉素异常的主要原因是嘧啶二聚体，一种紫外线诱导的DNA损伤，但6-4光产物，另一种紫外线诱导的DNA损伤也有贡献。在红土异常的剂量反应曲线上发现了清晰的阈值。UVC诱导的赤铁矿异常是非常特殊的赤铁矿，因为赤铁矿异常位于肺泡侧，频率不高。说明由于紫外线透过率不高，紫外线能量可能在成虫原始细胞所在的背侧表皮被特异性吸收，这种特异性吸收模式使得幼虫不易被紫外线杀死。

One of the important problems on studying anormality induced by chemicals, ionizing radiation and ultraviolet light (UV) is that where there is threshold (safety dose) as a function of dose. In Drosophila, after UVC irradiation of 1 st instar larvae which were grown in plain agar medium from the embryonic stage, the larvae were cultured in standard medium until they developed to adults. It was first found that high frequency of adult with tergite anormality were detected among the developed adults. It was investigated the existance of threshold, and the mechanism of larval lethality and the tergite anormality.Survival of larvae was defined as the ratio of the number of irradiated larvae to the number of developed adults and the frequency of tergite anormality was defined as the number of adults with tergite anormality by the total number of surviving adults. Using excision repair deficient and CPD photolyase deficient mutants strains, the major cause of the larval lethality and tergite anormality is pyrimidine dimer, a UV induced DNA damage, however 6-4 photoproducts, another UV induced DNA damage is also contributed. Clear threshold on the dose response curve of the tergite anormality was found. The UVC induced tergite anormality was very specific to the tergite, since the frequency of the sternite anormality which is placed in vental side, was not high. It is suggested that because transmittance of UVC is not so good , UVC energy might be absorbed specifically in the larval epidermis of the dorsal side where the primordial cells of adult tergite stay and this specific pattern of UVC absorbance makes larvae not easily be killed by UVC.