A 1.6 kb fragment encoding cre recombinase followed by the rabbit beta-globin polyadenylation signal was used to generate a targeting vector that replaced the translational start site of Foxl2 with the cre-ATG start codon by homologous recombination. The targeting vector contained a self-excising neo cassette (ACN cassette) and a diphtheria toxin-negative selection cassette (DTA). The ACN cassette was excised during passage through the male germline.