DPP analysis and histological analysis using electron microscopy showed that die4 protects retinal degeneration due to rdgC306 (Figure 3A–C, Figure S2), suggesting that Osi21 is not a specific regulator in norpA-triggered retinal degeneration but plays an essential role in retinal degeneration caused by intracellular accumulation of cytotoxic rhodopsin. This evidence concerns the gene RHO and retinal degeneration.