A synthetic splice acceptor site, exons 3 and 4, and an IRES-cre/ERT2 cassette were inserted into intron 2 along with a neo and thymidine kinase cassettes. Insertion was confirmed by Southern blot analysis and through crosses with reporter lines. Expression of cre is tamoxifen inducible and recapitulates endogenous promoter activity specifically in the central nervous system, eye, liver, heart, branchial arches and lymphatic endothelial cells.