The proposed origin of double minutes from Homogeneously Staining Region (HSR)-marker chromosomes in human neuroblastoma hybrid cell lines

Double minute chromosomes have been reported in a number of human and animal tumors although their origin and function in the cell remain unclear. The fusion of two cell lines without double minutes—a human neuroblastoma line containing another chromosomal abnormality, the homogeneously staining region (HSR), and a mouse fibroblast line—resulted in hybrid clones containing varying numbers of double minutes. The appearance of double minutes occurred coincident with the disappearance of the HSR. We propose that double minutes can originate from the breakdown of an HSR. The possible functional significance of these two chromosome abnormalities is discussed.