Further Observations on the Chromosomes of Chinese Hamster Cells in Tissue Culture 2

Abstract

The chromosome complements of 3 Chinese hamster cell strains and a methylcholanthrene-treated subline varied during observation periods of 12 to 22 months. The complements were formed basically from multiples of the haploid constitution, and in 1 strain the normal diploid complement persisted as the predominant pattern for many months. Abnormalities of varying types began to appear soon after a culture was initiated, and in some sublines particular abnormal chromosome patterns persisted for many months, while in others variation was continuous. Except in the rare, markedly polyploid and partially disintegrated metaphases, the normal morphology of the individual chromosomes was usually maintained. Thus the metaphase chromosomes could nearly always be identified, though exact similarity to the normal types was not found when deletions resulted in partial loss of chromosome arms. Telocentric chromosomes, not present in the normal diploid complement, were a feature of most strains and in some cases could be related to centromeric misdivision with persistence of 1 or 2 arms as functioning chromosomes. Other aberrant chromosome forms could not be identified with normal chromosome types. The changes in chromosome complements in these nonclonal cultures were fluctuating events unassociated with obvious changes in cultural or morphological appearances. A characteristic chromosome pattern with an unusual chromosome form appeared in a methylcholanthrene-treated subline of 1 cell strain, 5 months after exposure to the carcinogen. Subsequently, however, this characteristic pattern disappeared, and the chromosome complement of the treated subline did not differ significantly from the untreated parent cell strain.