A loxP site was inserted upstream of exon 11. An FRT-flanked neomycin resistance cassette with a 3' loxP site was inserted downstream of exon 13. Cre-mediated recombination removed exons 11 and through 13 (encoding the critical catalytic domain in dioxygenases) and the neomycin resistance cassette. RT-PCR confirmed the absence of transcript expression in the cortex, hippocampus and cerebellum. (J:201001)