Selection and adaptation for rapid growth in culture of cells from delayed sarcomas in XXXX .

@entity5 @entity19
More than 1000 cells of a spontaneously transformed line of BALB/3T3 cells are required to initiate @entity5 in half the @entity19 inoculated s.c., although the cells clone with an efficiency approaching 100% in culture. The cells of two @entity5 with prolonged latent periods, initiated by 2 X 10(4) and 5 X 10(3) cells, were chosen for detailed clonal analysis in culture. The cells from the @entity5 grew very poorly in culture in the first passages, but with increasing speed and efficiency in later passages. Cells derived directly from the two @entity5 cloned in agar with an efficiency of 0.01 and 0.002%. The growth rates on plastic of the rare successful clones derived from agar were generally low but extremely varied. Some clones lost the capacity for multiplication in a few passages, while others persisted but fluctuated unpredictably in growth rate in the early passages. The graded increase in growth rate of the uncloned @entity5 cell populations was probably the result of selection of the more rapidly growing clones. One of the slower-growing clones was subcloned. About half of the subclones grew at a slower rate than the parental clone. These, however, increased progressively in growth rate over six successive weekly passages, suggesting the occurrence of a gradual physiological adaptation. We conclude that selection of fast-growing clones contributes a major part of the gradually improving growth of @entity5 cell populations in culture, but that a physiological adaptation extending over many cell generations makes a significant contribution. The mechanism in either case is unknown, and indeed there may not be a unique mechanism in the scientifically rigorous sense.
