Expression of the Rb family during the cell cycle. (A-D) The E14.5 retinal explants were maintain in culture in the presence of [3H]thy for 1 h, washed and then maintained in culture for different periods. Dissociated retinas (dapi in A) were then immunostained for p107 (red in B) and overlaid with autoradiographic emulsion to detect the [3H]thy (C). The proportion of p107+ cells was then scored (250 cells in duplicate), and normalized data were plotted (D). The peak level of p107 was detected after 8 h of exposure, which coincided with the G2 and M phases of the cell cycle, and declined at 24 h, which coincided with the G1/G0 phase. (E-H) Similar experiments were done using P0 retinal explants and in P2 retinal explants (I-L). (H) The proportion of [3H]thy-labeled Rb+ cells from P0 retinal explants was high during 0 to 4 h of exposure (S, G2) and subsequently declined. (L) The level of [3H]thy-labeled p130+ cells in P2 retinal explants was low during the first 4 h (S, G2), peaked at 8 and 16 h (M phase) and then declined during G1/G0. Similar data for p27 are plotted as an internal reference for cell cycle phase estimates. Scale bars: A, E and I, 10 μm.