Cathepsin D in wild-type and Nuc1 RPE Cathepsin D in wild-type and Nuc1 RPE. Western blotting with cathepsin D antibody. Cathepsin D in wild-type and Nuc1 RPE. Western blotting with cathepsin D antibody. RPE samples were as follows: Lane 1, 2-month-old wild type; lane 2, 2-month-old Nuc1; lane 3, 8-month-old wild type; lane 4, 8-month-old Nuc1. The immature (inactive) pro-enzyme form of cathepsin is present in all samples. The mature (active) form of the enzyme is present in the wild-type samples, but is barely detectable in the Nuc1 samples. Actin is shown as a loading control. J. Samuel Zigler, Jr et al. J Cell Sci 2011;124:523-531 © 2011.