Fig. 1-17b: Targets of cell cycle regulatory effects of TSH, insulin/IGF-1 and TGFβ, as demonstrated in the dog thyroid primary culture system. Diamond/rectangle arrowheads represent inductions/repressions: the other dashed arrows are activations (+) and inhibitions (-). TSH (cAMP) does not induce cyclins D but assembles and then activates the cyclin D3-cdk4-p27 holoenzyme. IGF-1 and insulin allow the accumulation of the required cyclin D3. TGFβ inhibits the nuclear translocation of the cyclin D3-cdk4 complex, its association to p27 and its activation by TSH(cAMP). See text for full explanation.