Exon 1 was replaced by the tdTomato reporter gene, a Ptf1a coding sequence with an N-terminal epitope tagged Strep/Flag (NSF) fusion, and an FRT-flanked hygro cassette via RMCE using the loxed cassette acceptor (LCA) allele-containing ES cells. Flp-mediated recombination removed the selection cassette. (J:296396)