Tergite anormality induced by ultraviolet light in Drodophila melanogaster

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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.