A loxP site was inserted upstream of exon 10. An FRT-flanked neo cassette with a 5' loxP site was inserted downstream of exon 10. Flp-mediated recombination removed the neo cassette. Cre-mediated recombination removed exon 10, knocking out the short splice variant. The absence of the short form and expression of the long form was confirmed by western blot analysis. (J:170494)