E2f1, but Not E2f2 or E2f3, Loss Rescues Ectopic Division and Cell Death in the Rb KO Retina
(A) Retinal development. At E11 the retina is a NBL of dividing RPCs (white circle, green nuclei). RPC cell bodies oscillate along processes as they progress through the cell cycle. By P0 the NBL contains both RPCs and post-mitotic RTCs (coloured circles, red nuclei) and is separated from the GCL by the IPL. By P8 there are no RPCs, fewer RTCs, an OPL, and more differentiated rods (r) and cones (c) in the ONL; horizontal (h), bipolar (b), Müller (m), and amacrine (a) cells in the INL; and ganglion (g) and displaced amacrine cells in the GCL. Development is complete by ~P18.
(B) Rb is thought to regulate cell cycle and apoptosis by repressing E2fs, but to promote differentiation by potentiating tissue-specific transcription factors. However, Rb loss could also perturb differentiation through the indirect effects of abnormal division or death, and/or through direct regulation of differentiation genes by E2fs.
(C and D) Horizontal retinal sections of the indicated genotypes and ages were stained for nuclei (DAPI, blue), and (C) S-phase (anti-BrdU, red) or (D) apoptosis (TUNEL, red). Scale bars are 50 μm.
(E–G) Quantification of (E) all BrdU+ cells, (F) ectopic BrdU+ cells in GCL at P0, and (G) total TUNEL+ cells.
(H) Real-time RT-PCR analysis of E2fs and E2f target genes in P8 retinas of the indicated genotypes.
Error bars represent SD of measurements from three animals, and asterisks indicate a significant difference between the WT and indicated genotypes (*, p <0.05; **; p <0.01; ANOVA and Tukey HSD test for [E–G] and Fisher test for [H]).