Estimation in Vivo of DNA Strand Breaks and Their Rejoining in Thymus and Liver of Mouse

Summary

An alkaline sucrose-gradient centrifugation method capable of observing DNA strand breakage and rejoining has been used to observe non-dividing and slowly-dividing mouse thymocytes and hepatocytes in vitro and in vivo. The number of radiation-induced single-strand scissions of DNA in cell suspensions in vitro was always slightly greater than in vivo (0·8 ± 0·3 vs 0·6 ± 0·2 in thymocytes and 2 ± 1 vs 0·7 ± 0·4 in hepatocytes). The rejoining of single-strand scissions of DNA was detected in thymocytes both in vivo and in vitro; and in hepatocytes in vivo, but not in vitro during 60 min of incubation. In these systems, the number of radiation-induced breaks declined exponentially with time after irradiation, which suggests that an efficient rejoining system(s) is always present in mouse thymocytes and in hepatocytes.