A targeting vector was designed to flank exon 3 of the gene with loxP sites and insert a FRT-flanked neomycin resistance cassette in intron 3 (within the loxP sites). Resultant carrier mice were crossed with a germline Cre transgenic strain driven by a protamine 1 (Prm1) promoter on a mixed C57BL/6 and 129 background to remove both exon 3 and the neomycin cassette.