Using recombinase mediated cassette exchange (RMCE) a 532 bp fragment containing a GFP-Cre fusion protein replaced the entire coding region of the gene. The donor construct includes a frt-flanked pgk-hygromycin immediately downstream of the GFP-Cre fusion sequence. The frt-flanked pgk-hygromycin was removed by FLPe mediated recombination. Western blot analysis confirmed absence of protein in homozygotes. Green fluorescence is seen in pancreatic pre-endocrine cells and in islet cells after birth, in the developing central nervous system between E9.5 and E18.5, and also in the peripheral nervous system and gut endocrine cells. (J:94077, J:214095)