The CAG-driven SCAT3.1 (caspase-3-sensitive fusion protein) with an upstream floxed STOP cassette was inserted into the locus. SCAT3.1 contains a fusion of ECFP and the Venus EYFP analog connected by a caspase 3 cleavable peptide. Removal of the floxed STOP cassette is required for the expression of the caspase-3-sensitive reporter fusion.