Zebrafish eyeballs at different ages were lysed with SDS sample buffer (Beyotime, Shanghai, China), centrifuged for 1 minute at 9,000g, and the supernatant was collected. The 2X SDS-page loading buffer was equally added into the supernatant and then boiled for 10 minutes. Equal amounts of protein were separated by 12% SDS-PAGE and transferred onto a polyvinylidene difluoride membrane (Millipore, Bedford, MA, USA). The membrane was incubated in 5% milk (Sangon Biotech, Shanghai, China) for blocking, in the anti-myelin basic protein (MBP) antibody (1:1000, Abmart, Shanghai, China) and anti-β-actin (Cell Signaling, Beverly, MA, USA) for antigen-antibody recognition, and then in horseradish peroxidase–conjugated goat anti-rabbit IgG (1:10,000; Sango, Shanghai, China) for signal detection. Enhanced chemiluminescence detection kits (Thermo Fisher Scientific, Waltham, MA, USA) were used to visualize protein and films (Kodak, Rochester, NY, USA) were used to expose the membrane.