Evolution In Vitro of Stemlines With Minimal Karyotypic Deviations in a Human Heteroploid Cell Line2

Abstract

A comparative karyotypic study of human cell line C32 during 2 years' continuous in vitro growth was presented. All two sublines and four stemlines found in the C32 line had 45 chromosomes with a similar karyotype constitution, except for the subline- or stemline-specific marker chromosomes. The total chromosome length of hypodiploid C32 cells was longer than that of diploid cells. Of A-, C-, and D-group chromosomes involved in the marker chromosome formation, only C-group chromosomes deviated quantitatively from the disomic condition. The two sublines were readily distinguishable by the presence of the subline-specific ring (C32-R subline) or non-ring (C32-r subline) chromosomes. Four stemlines, however, differed only by either a loss of the marker chromosome 7 or an inclusion of a new marker formed by a balanced translocation between the M7 and a member of one of the only three C-group chromosomes remaining in disomic condition. These data strongly suggested the nonrandomness of karyotypic diversification of stemlines in in vitro culture system. Also, each stemline may have predominated a culture by a simple outgrowth without further chromosome modification. Thus abundant cells with an identical karyotype could be found between cultures separated by 2 years' continuous in vitro growth. Such a karyotypic stability of stemline populations was unusual because most heteroploid cell lines in continuous subcultivations often resulted in generation of vast karyotypic varieties within a short period of in vitro growth.