Math5 -lineage cells undergo apoptosis in Math5 -null retinas. Retinal sections from the control (top panels) and Math5-null (bottom panels) embryos at the indicated developmental stages were immunolabeled with anti-activated caspase-3 (red) and anti-GFP (green). (A-E) At E12.5 to E17.5, compared to the GFP+ apoptotic cells (arrows) occasionally seen in control retinas, the number of GFP+ apoptotic cells is significantly increased in Math5-null retinas. Insets in B-D indicate the enlarged views of boxed regions. Scale bar equals 100 μm. (F) Quantification of the GFP+/caspase-3+ cells per retinal section. Note: a, apoptotic cells negative for GFP were counted.