Mice with this conditional insertion, upon cre recombinase expression, produce a mutant neurogenin 3 protein in which serine has been replaced by alanine at amino acid positions 183 and 187 (S183A/S187A), eliminating a glycogen synthase kinase 3 beta (GSK3beta) consensus phosphorylation site, impairing its association with FBW7 and stabilizing the protein. The targeting construct was made by insertion of a cDNA encoding the full-length mouse protein with the introduced mutations into the Gateway compatible pROSA26-DV1 plasmid. The final construct contains a splice acceptor followed by a loxP-flanked Pgk-neor with a triple polyadenylation signal (STOP sequence), the modified Neurog3 cDNA, and an enhanced green fluorescent protein (EGFP) cDNA downstream of an internal ribosomal entry site (IRES). Deletion of the Pgk-neor-STOP by cre recombinase results in co-expression of NEUROG3-S183A/S187A and EGFP. (J:194078, J:215154)