Distribution of Breakpoints on Chromatid-type Aberration Induced by Three Different Radiations, in Relation to Fragile Sites

Abstract

Based on experimental evidence using human blood samples we able to suggest that 'common fragile sites' can be targets for different radiation sources. For that we used peripheral blood samples from three healthy adult donors and exposed them to 60 Co γ-rays (2, 4 Gy) or neutrons (0.8, 2 Gy) at the G 2 stage. In another set, normal bone marrow cells from 19 adult donors were also exposed to 60 Co γ-rays, tritiated water β-rays, and 252 Cf neutrons and sampled 24 hr later. Chromatid breakpoint were identified using Wright's stain G-banding. Analyses of 912 breakpoint detected in lymphocytes and 545 breakpoint detected in bone marrow cells were within the same bands as 113 reported: (1) 41% - 52% of chromatid breakage had a chromosome band of relative fragile sites in both bone marrow cells and lymphocytes; (2) the breakage induced by different radiation sources were distributed in a similar pattern; (3) significantly higher numbers of breakpoint were found at 4q31, 2q35, 3p21, 5q31, 1q32, 2q31, 15q24 and 13q22 in lymphocytes, and at 3p21, 14q24, 17p13, 1q42, 7q22 and 9p11/q11 in bone marrow cells; (4) distribution of breakage was similar between lymphocytes and bone marrow cells except for certain breakpoints. Present study also revealed that a B-cell line established from lymphocytes with a history of 60 Co γ-ray irradiation had more chromosome breakpoints at telomere regions than no-irradiated cell line, which indicating telomere protein might be associated with radiation-induced chromosome instability. This study provides information that will be useful for increasing our understanding of the mechanisms that underlie radiationinduced chromosome aberrations and will aid in assessing genetic and cancer risks in radiation-exposed human populations.