Transduction with GFP and hTERT/GFP.

(A) Progressive loss of telomere fluorescence in subclones transduced with GFP vector (G11.8 and G11.1). (B) Elongation or maintenance of telomere fluorescence in subclones transduced with hTERT/GFP vector (T11.9, T11.14, T11.7 and T11.10). Eight clones were analyzed by flow FISH after each cloning (mean ± SD) and a single clone with average telomere length was picked for subsequent recloning; bp indicates base pair; PD, population doublings; n = 5, telomere fluorescence analysis of only 5 clones. Arrows represent the replicative senescence stage observed after the fifth round of cloning in subclones G11.1 and G11.8.