Chromosomal replication asynchrony of a human breast carcinoma cell line. I. studied by continuous BrdU incorporation and G-banding analysis.

Continuous BrdU incorporation and the Giemsa staining technique were used to study the cell cycle kinetics of a human breast tumor cell line. It was found that the interchromosomal replication pattern of the neoplastic cell was significantly different from that of normal cells in two respects. First, the pattern is highly asynchronous; within a single cell there are chromosomes at different replication cycles; that is, some chromosomes complete their DNA replication before others begin. Second, the replication schedule for the chromosomes, as identified by superimposing the BrdU-Giemsa technique on the trypsin G-banding technique, is relatively consistent within the cell line but differs from that of normal cells. Some chromosomes that replicate late in normal human lymphocytes and fibroblasts replicate early in this cell line. In contrast to the unusual interchromosomal replication pattern, gross analysis of the intrachromosomal replication schedule shows no apparent difference from that reported for normal cells. The asynchrony phenomenon reported here may be associated with the etiology of aneuploidy in neoplasia.