An FRT flanked neo cassette with a 5' loxP site was inserted upstream of exon 5. An additional loxP site was inserted downstream of exon 7. Flp-mediated recombination removed the neo cassette leaving exons 5 through 7 floxed. An 84% reduction in protein expression was confirmed by western blot analysis on E13.5 brain extracts (J:170581)