Autoradiographic study of chromatid distribution of labeled dan in two types of mammalian cells in vitro

Summary

The average generation time and the length of the G1, S, and G2 periods were determined for a line of Chinese hamster cells in vitro. On the basis of this information, cells were labeled with ³H-thymidine and the segregation of radioactive DNA in chromatids at metaphase was studied for four consecutive divisions after labeling. In preparation for autoradiography the metaphase chromosomes were freed of cytoplasm. This technique eliminated beta absorption by overlying cytoplasm and permitted an analysis of 80 to 100 per cent of the chromatids of each cell. Autoradiographs of several thousand chromosome sets of each of the four divisions after labeling were examined. The labeled DNA segregated according to a semiconservative pattern. This finding is in agreement with the work of Taylor and is not in accord with the results of Plaut and Mazia and La Cour and Pelc. The frequency of sister “chromatid exchange” was lower than observed by Taylor in plant chromosomes.

The same pattern of semiconservative segregation of DNA was found in human leucocytes in vitro. The frequency of sister “chromatid exchanges” also was low in this material.