Progressive degeneration of photoreceptor cells in cyp4v7/cyp4v8 DKO zebrafish. (A) Histological analysis revealed the progressive degeneration of the outer retinal layer in cyp4v7^−/−cyp4v8^−/− zebrafish. OS, outer segment; IS, inner segment; ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer. Scale bars: 20 µm. (B) The quantitative results of the thickness of OS layer (represented by the length from the lower edge of IS to the upper edge of RPE) in A. Three parallel samples were tested for each group. The results are shown as mean ± SD. ***P < 0.001; **P < 0.01. (C) Western blotting analysis of Gnat1 and Gnat2 protein levels in WT and mutant zebrafish retinas at 10 and 12 months after fertilization. Tubulin was used to normalize protein loading. (D) Quantitative analysis of the Western blot data. At least three independent experiments were performed and quantified. The results are shown as mean ± SD. ***P < 0.001; **P < 0.01.