Table 1.

Population doubling time (in hours) in different types of NIH/3T3 fibroblasts as calculated with the formula 1 (see Material and Methods for detail) after cell culturing without (-Dox) or with (+Dox) 100 ng/ml doxycycline for 24 or 48 hours. The data are expressed as the mean ± SEM (Standard Error of the Mean). At 24 hours of post-induction, the values observed in –Dox and +Dox NIH/3T3-174 fibroblasts differ statistically significantly (t-test, p < 0.001) and are shown in bold. The population doubling time in –Dox NIH/3T3-174, -Dox NIH/3T3-EGFP, +Dox NIH/3T3-EGFP and parental NIH/3T3 fibroblasts do not differ significantly (p > 0.05). At 48 hours, the population doubling-time between different fibroblasts differs insignificantly (p > 0.05).

	Cell population doubling time (in hours)
Investigation time-point	NIH/3T3-174 (-Dox)	NIH/3T3-174 (+Dox)	NIH/3T3-EGFP (-Dox)	NIH/3T3-EGFP (+Dox)	Parental NIH/3T3 (-Dox)
24 hours	19.8 ± 0.7	16.2 ± 0.5	19.0 ± 0.2	19.6 ± 0.9	18.2 ± 0.2
48 hours	21.9 ± 1.9	26.6 ± 1.5	23.3 ± 2.5	27.7 ± 5.4	24.2 ± 3.2