After inducing retinal degeneration using 150 mg/l MNU, maximal activation of the TGFβ pathway occurred between days 3 and 8 as demonstrated by immunohistochemistry for phosphorylated Smad3 (P-Smad3) (Fig 1; representative immunohistochemistry for day 5 is shown). This evidence concerns the gene SMAD3 and retinal degeneration.