UV-A breakage sensitivity of human chromosomes as measured by COMET-FISH depends on gene density and not on the chromosome size

COMET-FISH, a single cell-based combination of COMET-assay (also known as s ingle cell gel electrophoresis (SCGE)) with fluorescence in situ hybridizat ion (FISH) allows region specific studies on DNA stability and damage. COME T-FISH can be used to investigate UV-A-induced DNA damage of selected whole chromosomes. In the present work, a modified COMET-FISH protocol with whol e chromosome painting probes was used to study whether UV-A-induced DNA dam age is distributed randomly over the whole genome or occurs at preferred si tes. The study was performed with 12 different chromosome painting probes ( for chromosomes 1, 2, 3, 8, 9, 11, 14, 18, 19, 21, X and Y). The results on human lymphocytes irradiated with 500 kJ/m(2) at a wavelength of 365 nm in dicate that the induced number of chromatin strand breaks does not correlat e with the chromosome size. They therefore are distributed in a non-random manner. For example, fragments of the gene-rich chromosome chromosome 1 wer e found in the comet tail in only 3% of the examined cells, and thus chromo some 1 is rather stable, whereas fragmentation of the gene-poor chromosome 8 was observed in 25% of all comets. On the basis of all 12 chromosomes ana lyzed, an inverse correlation between the density of active genes and the s ensitivity toward UV-A radiation is found. (C) 2000 Elsevier Science S.A. A ll rights reserved.