A construct containing Hoxb8 upstream sequences, a FlipO recombinase cassette, and a bovine poly(A) sequence inserted in-frame downstream of the Hoxb8 ATG site was used. Fertilized early-stage C57BL/6J oocytes were injected with the linearized construct, and two founders were obtained. Founders were mated to generate transgenic lines, one of them, F11, exhibited the expected expression pattern of Hoxb8 at P0.