Figure 2.

Effect of MTX pretreatment on cloning efficiency of three sublines. Cells (10⁴) of the A′, SA′, and 4° SA′ sublines were treated with 200 nM MTX during the growth curves of Fig. 1. On each successive day for 4 days, treated and untreated cultures were trypsinized, and 100 cells were reseeded in MCDB 402 with 10% CS without MTX. They were incubated for 6 days, fixed, and stained, and the number of colonies were counted in a stereomicroscope. A′ cells, ▪; SA′ cells, •; 4° SA′ cells, ▴.