Reciprocal compensation after Rb or p107 inactivation. (A) Real-time PCR analysis of Rb expression in retinas from three developmental stages of p107-deficient or wild-type mice. At E13.5, Rb was upregulated. Analysis was done in triplicate samples analyzed in duplicate. (B) In a similar experiment, p107 expression was analyzed in Rb-deficient retinas. Due to the embryonic lethality of deleting Rb, cultured retinas were used for the later stages; p107 was upregulated in a compensatory manner. (C) A summary of the changes in Rb family gene expression after Rb or p107 inactivation. (D) E13.5 p107-deficient retinas were labeled with [3H]thy for 4 h and immunostained for Rb expression (red). (E) In a similar experiment, cultured Rb-deficient retinas were labeled for p107 expression. (F, G) In the absence of Rb in Chx10-Cre;Rb
Lox/- P12 retinas, rod photoreceptors failed to form, and chromatin failed to condense in the ONL (arrow). (H) Chromatin (arrow) in rod photoreceptors normally condenses during differentiation. (I) In the absence of Rb, rods remained immature with diffuse chromatin (arrow). (J) These defects in cell-fate specification also caused defects in synaptogenesis of horizontal cells (arrows); with processes extending apically into the ONL. (K-N) Wild-type and Rb-deficient E13.5 retinas were immunostained with an antibody against Brn3b (red), a ganglion cell marker. Brn3b was distributed across the retina (green nuclear stain overlay) and was indistinguishable in the presence or absence of Rb. (O-R) Wild-type and p107-deficient E15.5 retinas were immunostained for p57Kip2 (red), which was expressed in a subset of retinal progenitor cells and newly postmitotic amacrine cells. (S) PSD95 (red) was expressed in the OPL and was normally distributed in the absence of p107. (T) Amacrine cells stained with tyrosine hydroxylase were also distributed normally. (U, V) Cone photoreceptors, (W, X) calretinin+ amacrine cells and (Y, Z) amacrine cells and horizontal cells were distributed normally in the p107-knockout retinas. Abbreviations: DIC, days in culture; INL, inner nuclear layer; IPL, inner plexiform layer; ONL, outer nuclear layer; OPL, outer plexiform layer. Scale bars: B, D, F, H, L, N, P, T and U, 10 μm; I and J, 25 μm.