Chromosomal radiosensitivity and karyotype in mice using cultured peripheral blood lymphocytes, and comparison with this system in man.

The frequencies were studied X-ray-induced dicentric chromosomes and deletions in peripheral blood lymphocytes of mouse and man, cultured in vitro. After doses of 100 and 200 rad, (a) the mouse was equally sensitive as man to the induction of dicentrics, and (b) the frequency of deletions was higher in the mouse, reaching statistical significance at the 200 rad level only. At the 200 rad level, the mouse with normal karyotype was compared with the T(1;13)70H translocation heterozygote and the Ts(1(13))7OH tertiary trisomic of normal appearance. No differences were found either with respect to dicentrics or to deletions. At the 100 rad level, the normal mouse was compared with the tertiary trisomic mouse of the affected phenotype and with the tobacco mouse. The frequency of dicentrics was significantly higher in the phenotypically abnormal trisomics, whereas the deletion frequency was higher in the tobacco mice. C-banding of the slides enabled the locating of breaks in constitutive hetero-chromatin and euchromatin. When exchanges were classified into three categories, i.e. those between eu- and euchromatin, eu- and hetero-, and hetero- and heterochromatin, there was a preference for the first and the last whereas only few occurred between chromatins of contrasting type. Differences between previous determinations of the chromosomal radiosensitivity of mouse and man, using peripheral blood lymphocytes (i.e. man is twice as sensitive as mouse), and the one presented here could be attributed to differences in harvest time of the mouse peripheral blood lymphocytes. Thus the so-called "arm number" hypothesis of Brewen et al. [5] is not confirmed by the present results.