A new chromosome region possibly derived from double minutes in an in vitro transformed epithelial cell line

Double minute chromosomes (DMs) are reported for the first time in in vitro transformed mouse epithelial cells. In one cell line, CSG 122/17, DMs persisted through numerous passages. A subpopulation appeared in this line at passage 23, in which the DMs had disappeared but were replaced by a finely banded chromosome region possibly associated with the distal end of chromosome 5. In a second cell line, CSG 120/7, there was no evidence of DMs in the earliest frozen stock available. However, a finely banded region similar to that found in CSG 122/17 was present and was again associated with chromosome 5, in this case with the proximal end. The possible evolution of these new chromosome regions from DMs is discussed.