To understand the role of FGFR3 in bladder cancer biology, we knocked in the cDNA of human FGFR3 encoding the S249C mutation under control of a LoxP-Stop-LoxP cassette into the collagen type 1, α1 (Col1a1) locus to generate mice harboring the Col1a1-LSL-FGFR3S249 allele (hereafter called LSL-FGFR3S249C) (Figure 1A). Here, FGFR3 is linked to urinary bladder cancer.