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. This allele is a hypomorph, although RNA levels are not altered, WAPL protein levels are reduced by 2 fold.