Table 2.

Duration (in hours) of cell cycle phases in sub-confluent NIH/3T3-174 fibroblasts cultured without (-Dox) or with (+Dox) 100 ng/ml doxycycline for 24 hours after seeding. In brackets, the formulae used for calculations are indicated (see Materials and Methods for detail). The percentage of cells at G0/G1, S and G2/mitosis phases was determined by flow cytometry. The percentage of G0 cells was measured by cell population culturing with Br-dU for 24 hours. The number of G1 cells was as the number of G1/G0 cells minus the number of G0 cells. Data are expressed as the mean ± SEM. The compared pairs of values, which according to the t-test, differ significantly (p < 0.05) are indicated in bold. The duration of the cell division cycle in -Dox cells (17.6 ± 0.6) and in +Dox cells (14.0 ± 0.4) differ with p < 0.001.

	NIH/3T3-174 -Dox (control)		NIH/3T3-174 +Dox
Parameters	Cell number (%)	Duration (hours)	Cell number (%)	Duration (hours)
G0 period	15.0 ± 2.4		18.0 ± 3.4
Cell division cycle(2)		17.6 ± 0.6		14.0 ± 0.4
G1 phase(5)	34.6 ± 1.9	5.7 ± 0.4	28.2 ± 2.0	3.8 ± 0.3
S phase(4)	40.5 ± 2.0	9.0 ± 0.4	44.9 ± 2.6	8.1 ± 0.4
G2 phase+mitosis(3)	9.9 ± 1.2	2.8 ± 0.3	8.9 ± 0.6	2.1 ± 0.1