The targeting vector is designed to insert a loxP site upstream of the endogenous promoter (- 517 bp relative to major transcriptional start site), and a loxP site downstream of exon 2 (+3641 relative to the major transcriptional start site). An FRT-flanked neomycin cassette is also part of the construct. Flp-mediated recombination removed the neo cassette. Cre-mediated recombination removed the promoter and exons 1 and 2. (J:331699)