Exon 2 was replaced with a floxed full-length Gata4 cDNA with a transcription STOP sequence followed by an alkaline phosphatase gene with a 3' frt site. An frt-flanked neo cassette used for selection purposes was removed by germ line, flp-mediated recombination. Cre mediated recombination is necessary to activate alkaline phospatase expression. (J:137426)