The starting ATG codon as well as codons 2-4 of exon 1 were replaced with a lacZ-floxed PGKneo cassette. The neo cassette was in the same transcriptional orientation as the gene itself. In vivo cre excision was accomplished by crossing to Tg(ACTB-cre)2Mrt transgenic mice. After cre excision of neo, beta galactosidase staining was reduced in intensity but the overall pattern of staining was maintained.