Exons 2 and 3 were flanked by lox sites and an FRT flanked neo cassette and a 29 bp deletion for genotyping were inserted in intron 3 via homologous recombination. Cre mediated recombination removed the selection cassette and exons including the translational start site. Protein was undetectable by immunofluorescence after E3.5. (J:155958)