standing of stress response mechanisms, which play an important role in the pathogenesis of many diseases and in aging processes. In high doses, adverse effects accumulate in the tissues in a deterministic manner that depends linearly on the dose. The mechanisms of the low-dose irradiation effects are the most obscure stress response mechanisms. In low doses the effects are stochastic, non-linear, and depend mainly on the efficiency of the stress response’s protective mechanisms, such as anti-radical protection, DNA repair, and detoxification of xenobiotics. Any differences in the pattern of gene expression that depend on the influencing factors can be used to biosense each of the pollutants in low doses, providing a deeper understanding of their mechanisms of action and identifying both the similarities and differences in their action. For example, this sort of transcriptional signature identification has been performed for most drugs. In this study, we use a systems approach to analyze the effects of formaldehyde, toluene, dioxin and low doses of ionizing gammairradiation on the expression of 25,415 transcripts obtained by RNA-seq analysis in adult wild-type Drosophila males and females. Functional analysis identified exposure-specific genes and biological processes, and the overall effects reflect a non-specific stress response. We also observed that the sex-specific differences in the transcriptome are more pronounced than the effects on expression caused by the above-mentioned stressors. Materials and Methods Drosophila Melanogaster Strains In our experiments, we used laboratory wild-type males and females. The line was obtained from the collection at the Bloomington Drosophila Stock Center at Indiana University. Flies Maintenance Conditions The control- and experimental flies were maintained in the dark at T 2560.5uC on a sugar-yeast medium containing 7 g of agar, 30 g of sugar, 8 g of dry yeast, 30 g of semolina, 4 ml of propionic acid, and 1 liter of water. Males and females were kept separately at densities of 20 flies of the same sex and age per 120 mL vial. Treatment by Ecotoxicants For analyzes of the expression profiles the 5-day-old flies were used for each control- and experimental variants. For each variant 2 biological replicates were pooled. Number of flies for each control- and experimental variants in 2 biological replicates were 40. Experimental flies were exposed to gamma-irradiation from 226 Ra source with the dose rate of 36 mGy/h. The exposure time was 5 h 34 min; the absorbed dose 20 cGy. The dose of 20 cGy is the upper limit of low dose range of low-LET radiation. The irradiation of Drosophila in doses of 4060 cGy is known to induce the hormetic effect on the lifespan,. In order to investigate the effect of 2,3,7,8-tetrachlorodibenzop-dioxin on gene expression profile, TCDD, which was dissolved in MedChemExpress A-83-01 toluene PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19653627 as solvent, was compounded with growth medium. Flies were incubated on growth medium with 0.822 mM/L TCDD for 3 days. As toluene was a solvent for TCDD, we fed flies an equivalent amount of toluene in growth medium as vehicle control for TCDD. Flies were incubated on growth medium with toluene for 3 days. To exclude specific influence of fresh media on gene expression it was changed in all control- and experimental variants simultaneously. For treatment in the vapor of a 7% formaldehyde solution, flies were placed in a specially designed vial for 24 hours. The formaldehyde solution was produced using formalin