INDUCTION AND PERSISTENCE OF CYTOGENETIC DAMAGE IN MOUSE SPLENOCYTES FOLLOWING WHOLE-BODY X-IRRADIATION ANALYZED BY FLUORESCENCE IN-SITU HYBRIDIZATION .1. DICENTRICS AND TRANSLOCATIONS

Chromosome translocations (stable aberrations) can persist longer duri ng cellular proliferation than dicentrics (unstable aberrations). It i s important to know the kinetics of the elimination of dicentrics and to what extent translocations persist in an in vivo cell population af ter irradiation. The female Swiss mouse were used to study the inducti on and persistence of dicentrics and translocations in splenocytes up to 112 days after exposure to 2 Gy whole-body X-irradiation. Metaphase spreads at different time intervals were analyzed by fluorescence in situ hybridization (FISH) using chromosome-specific DNA libraries for chromosomes 1, 11 and 13. The frequencies of dicentrics and translocat ions appear to be equal immediately after irradiation. Frequencies of dicentrics decreased exponentially with time according to the relation ship D = ae(-kt). The rate of elimination was faster in the early peri od (days 0-14) than in the later period (greater than or equal to 14 d ays). The frequency of translocations was constant in the period 0-7 d ays and then decreased linearly or exponentially. For the whole period , the trend is highly significant. As mouse chromosome painting probes are becoming available and by using FISH, an in vivo mouse model for the analysis of translocations has become feasible. As translocations are involved in carcinogenesis and genetic disorders, risk estimation for induction of translocations by ionizing radiation can be made with greater confidence and extrapolated to the human situation.