In a step wise targeting process a floxed neo cassette was inserted downstream of exon 8. This was followed by removal of the neo leaving a single loxP site. Then an FRT flanked neo cassette and loxP site were inserted upstream of exon 5. Flp mediated recombination removed the neo leaving exons 5 -8 floxed. Finally, cre mediated recombination removed exons 5 - 8. (J:321165)