Progressive thinning of ONL in Mef2d−/− and Mef2c−/− mice. (A–D) H&E staining of Mef2d+/+ and Mef2d−/− retinas at P14 (A), P30 (B), P60 (C), and P180 (D). (E, F) Representative images of H&E stained retinal sections of Mef2c+/+ and Mef2c−/− retinas at P14 (E) showing normal structural phenotype, and at P30 (F) showing dramatic loss of photoreceptors in Mef2c−/− with only a single row of photoreceptors remaining. Scale bars: 20 μm.