Heterogeneity of Chinese hamster X chromosomes in X-ray-induced chromosomal aberrations

To study the frequencies and distribution of X-ray-induced chromosomal aberrations in different arms as well as different regions of the long arms of Chinese hamster X chromosomes by fluorescence in situ hybridization (FISH).

Female embryonic primary cells of Chinese hamster were exposed to 1 and 4 Gy X-rays during the G1 stage and metaphases were collected 20 h later with colcemid-blocking. Induced aberrations involving different arms as well as different regions of the long arm of the X chromosomes were analysed by three-colour FISH using arm-specific painting probes. Distributions of aberrations in the arms were statistically analysed by chi2-test, with the hypothesis that aberrations are proportionally distributed on the basis of their relative lengths of the arms.

The long arms of the X chromosomes were frequently involved in breaks than was the short arm. The result of the chi2-test indicates a non-proportional distribution of breaks between the arms, while exchanges (dicentrics and translocations) involving the arms were proportionally distributed. Differential involvement of regions of the long arm, i.e. Xq1 and Xq2, in breaks was also observed. Xq21, a known common fragile site in the X chromosome, was often involved in terminal deletions.

Arm-specific probes of Chinese hamster chromosomes are useful for the detailed study of X-ray-induced aberrations in the X chromosome. The heterogeneity of the Chinese hamster X chromosome in response to X-ray-induced aberrations exists not only between the short (euchromatin) and the long (heterochromatin) arms, but also between different heterochromatic regions of the long arm of the X chromosome.