This mutant is derived from Rb1tm1Jyjw. The floxed neo cassette in intron 25 was removed by mating Rb1tm1Jyjw animals to cre-expressing line TgN(Prm-cre)58Og. Resulting progeny contain the aspartic acid to alanine mutation in the caspase cleavage site of exon 25 and the diagnostic EcoRI site in intron 24.