Chromosomal Variability in Clonal Populations of a Chinese Hamster Cell Strain

Abstract

Numerical and structural chromosome variations and morphological characteristics of 9 clones derived from strain FAF28, previously cloned 5 times in Boston (Blld-ii) to assure euploidy, were studied. All 9 clones could be divided into: (a) hypo-diploid (modal number of chromosomes 19–20), (b) diploid, and (c) hyperdiploid (modal number from 24–28). Morphologically, hypo-diploid clones were fibroblast-like, hyperdiploid clones were epithelial-like, and diploid clones showed an intermediate type of growth. During 7 to 10 months of cultivation, the evolution of karyotypes of stem cells was observed in 6 of 9 clones, with a tendency of modal classes to shift toward diploidy. Karyotypes having 20 chromosomes were replaced by ones with 21 and 23, and those having 28 and 27 were replaced by complements with 27 and 26 chromosomes, respectively. Structural variants of karyotype were noted among cells with the same chromosome number. In the clones, different chromosome types were responsible for deviations from the diploid number. In hypo-diploid cells the decrease in chromosome number was due to the loss of small metacentric chromosomes(m), the number of large metacentrics(M) remaining unchanged or slightly increased. The number of subtelocentrics (St) did not change significantly. In diploid (pseudodiploid) cells, the decrease in the number of M chromosomes invariably coincided with an increase in the number of St chromosomes. In hyperdiploid cells, the additional chromosomes were of the m or St groups; the number of M chromosomes was essentially normal. Various forms of marker chromosome were noted in the different groups of clones. A correlation of numerical and structural chromosomal variants, as well as the direction of evolution of stem lines in clonal cell populations, indicates that their maintenance (viability and functional) may depend on the rather narrow limit of the total amount of chromosomal material present.