Figure 12.

Double immunofluorescent labeling of cyclin D3 (using DCS-22 without unmasking treatment) or cdk4, and PCNA used as a cell cycle marker. Quiescent dog thyrocytes were stimulated for 26 h with TSH (1 mU/ml) + TGFβ (2 ng/ml). Large arrows and medium size arrows show cells identified, respectively, in late G1 and S phases as described previously (Baptist et al., 1993) (the speckled appearance of PCNA-labeled S-phase nuclei was clearly seen at microscope but not in these digitalized micrographs). Small arrows show G0/G1 cells with a low PCNA staining. The microscopical fields were selected to contain cells that escape the TGFβ inhibition of proliferation. Notice that all the PCNA-positive cycling cells display intense nuclear stainings of cyclin D3 and cdk4.