BAC recombineering was used to insert a loxP site upstream of exon 2 and a neomycin resistance cassette flanked by FRT sites downstream of exon 3 followed by another loxP site. The neomycin selection cassette was removed via FLP-mediated recombination by breeding with Tg(ACTFLPe)9205Dym expressing mice, leaving exons 2 and 3 flanked by loxP sites. mRNA and protein expression of the adjacent Masp2 gene (in which the 2 last exons of Masp2 overlap with the 3' untranslated region) is reduced by about 50% in heterozygotes. Western blot analysis confirmed Taradbp protein expression in the brain, spinal cord, and liver tissue.