Comparison of the patterns of chromosomal late replication. I. Human renal epithelium and lung fibroblasts in vitro.

The patterns of late replication of human fetal lung fibroblasts and renal epithelium in culture were compared using a terminal pulse of 3H-TdR or of BrdU followed by autoradiography or Hoechst and Giemsa staining, respectively. Fifty cells from each of two fetuses were scored with each technique. Statistically significant quantitative differences were found in the pattern of late replication of the two tissues, but these differences were not consistent between the two individuals. In cultures from both of the fetuses examined, the autoradiographic grain counts over a given segment of chromosomes 1, 4, and 5 in the two tissues were shown to differ by a factor of 2 or more, while with BrdU chromosomes 1, 2, 4, and 13 had a labeling frequency that differed by 20% or more over a given band. The results suggest that although there are tissue-specific differences in the patterns of late replication, these differences do not reflect changes in the state of differentiation.