Exon 17 was flanked with a loxP site and a floxed neo cassette via homologous recombination. The neo cassette was subsequently removed via in vivo Cre-mediated recombination leaving exon 17 flanked by 2 single loxP sites. Cre mediated removal of exon 17 will result in a frameshift, premature termination codon and truncated protein. (J:131043)