NO EVIDENCE FOR THE IN VIVO INDUCTION OF GENOMIC INSTABILITY BY LOW DOSES OF 137CS GAMMA RAYS IN BONE MARROW CELLS OF BALB/CJ AND C57BL/6J MICE

In spite of extensive research, assessment of potential health risks associated with exposure to low-dose (<= 0.1 Gy) radiation is still challenging. We evaluated the in vivo induction of genomic instability, expressed as late-occurring chromosome aberrations, in bone-marrow cells of two strains of mouse with different genetic background, i.e. the radiosensitive BALB/cJ and the radioresistant C57BL/6J strains following a whole-body exposure to varying doses of Cs-137 gamma rays (0, 0.05, 0.1, and 1.0 Gy). A total of five mice per dose per strain were sacrificed at various times post-irradiation up to 6 months for sample collections. Three-color fluorescence in situ hybridization for mouse chromosomes 1, 2, and 3 was used for the analysis of stable-aberrations in metaphase-cells. All other visible gross structural-abnormalities involving non-painted-chromosomes were also evaluated on the same metaphase-cells used for scoring the stable-aberrations of painted-chromosomes. Our new data demonstrated in bone-marrow cells from both strains that low doses of low LET-radiation (as low as 0.05 Gy) are incapable of inducing genomic instability but are capable of reducing specific aberration-types below the spontaneous rate with time postirradiation. However, the results showed the induction of genomic instability by 1.0 Gy of Cs-137 gamma rays in the radiosensitive strain only.