Cells

Cells were isolated from eight male bank voles from the Chernobyl exclusion zone (GPS coordinates N51.44536 E30.06522) and eight male voles from Kiev area (N50.525859 E30.436933) (Additional file 4). Bank voles were caught using Ugglan Special2 multiple-capture live traps (Grahnab, Sweden) during June of 2016. The level of soil radiation at the trapping sites were measured at one cm above the ground using a Geiger-Mueller dosimeter (Inspector, International Medcom INC). Selected bank voles were of similar size (length: x_CTRL = 24.5 cm, x_CHERNOBYL = 21.9 cm, Student’s t-test p-value = 0.06; weight: x_CTRL = 88.7 g, x_CHERNOBYL = 92.1 g Student’s t-test p-value = 0.08). Animals were euthanized by cervical dislocation and all the procedures were performed in accordance with international guidelines and regulations for the use of animals in research. The study was approved by the Finnish Ethical Committee (license number ESAVI/7256/04.10.07/2014).

Skin fibroblasts were isolated 1–4 h after the animals were sacrificed according to the protocol of Seluanov [36]. In short, about one cm² area of shaved skin from armpit of the animal was clipped and put into PBS for 10 min and then cut into small pieces and incubated at 37 °C in DMEM (30%) / PBS (70%) / Liberase DL Research Grade Enzyme (500 μg/ml) (Sigma-Aldrich) for 30 min. The tissue was filtered through 70 μm nylon mesh and placed into cell culture tube with DMEM (high glucose, GlutaMAX™) / 20% FBS / penicillin (100 U/ml) / streptomycin (100 μg/ml) / amphotericin B (1 μg/ml) (all from Thermofisher) and incubated at 37 °C for 2 days.

Cells were routinely cultured at 36 °C / 80% humidity / 5% CO₂ in DMEM / 10% FBS / penicillin / streptomycin / amphotericin B. All experiment were done with similar passage numbers for both control and Chernobyl cells between passages 5–30. After cell passage 30 some of the cell lines showed chromosomal number abnormalities.