This allele was created by RMCE in Gt(ROSA)26Sortm1Mgn. The original selections cassettes (puromycin N-acetyltransferase and a truncated form of HSV1 thymidine kinase and EM7-driven neomycin resistance) were replaced by a cassette composed of ROSA26 upstream sequence deleted from the start codon to -60, mutant TCF/LEF binding sites from the Ctnnb1 gene controlling expression of the CFP reporter. An upstream FLP flanked hygromycin selection cassette was subsequently removed by flp recombinase.