Figure 3.

Inhibition by TGFβ of TSH-induced cell cycle progression (A) and accumulation of cell cycle regulatory proteins (B). Four-day-old dog thyrocytes were stimulated at 0 h with TSH (1 mU/ml) or remained in control (C) condition. TGFβ₁ (2 ng/ml) (β) was administrated at the same time or 15 h after TSH. (A) Kinetics of cell cycle progression evaluated by the determination of the percentage of PCNA-positive cells identified as described (Baptist et al., 1993) in G1 and S phases. PCNA-negative cells are either in G0 or at a G1 stage before PCNA appearance. (B) Accumulation of cdk4, cdk2, cyclin A, and cdc2 assessed by Western blotting in the same experiment.