[A study of the UV-sensitivity in Drosophila strains with different repair abilities]

Sensitivity of Drosophila embryos to lethal effect of UV rays was studied in mutants rad202G1 and mei-9a (a homologue of the gene for xeroderma pigmentosum) that are deficient in excision repair, the mutant mei-41D5 (a homologue of the gene for AT) with distorted check-point function in the cell cycle, and wild-type line Oregon R. The mortality of embryos, which were exposed to radiation within the 0.5-16-h interval of embryonic life, served as a criterion of sensitivity. During this interval of embryogenesis, the multicellular system of Drosophila embryo sequentially consecutively passes through a set of well studied cell cycle modifications. It was of interest to compare UV sensitivity at these stages recorded at the organism level. The induced embryonic lethality was tested by means of determining the dose-effect relationship followed by an estimation of corresponding values of the LD50 dose characterizing the pattern of age-associated changes of the character. The obtained data were analyzed in relation to the specificity of the mutagenic effect of UV irradiation, the features of Drosophila development, and repair deficiency of each studied mutant. The interval of the pronounced effect of UV irradiation on embryo viability was shown to be limited to 13 h from the beginning of embryonic life. During this interval, the UV sensitivity of embryogenesis in mutant lines is much higher than in the line of normal genotype. Moreover, at the level of LD50 doses that individually characterize each line, this sensitivity did not exhibit a relation to the mitotic status of cells, in contrast with the effects of rarely ionizing radiation. UV-inducible embryo lethalities that are caused by the mortality of dividing and nondividing cells are whether equal (line Oregon R and mutants rad202G1 and mei-41D5) or even extremum in the case of damage of amitotically growing cells (the mei-9a mutant). Possible mechanisms of these manifestations are discussed.