(D) Rescue of Rb KO SACs by E2f3a deletion. Horizontal retinal sections of the indicated genotypes and ages were stained for nuclei (DAPI, blue), M-phase (PH3, green), and the SAC marker Slc18a3 (red). E2f3a deletion does not suppress ectopic division, but rescues the SAC defect. Scale bars are 50 μm.