En1^tm8.1Alj

A targeting construct was designed to insert an frt-flanked neomycin cassette and loxP site upstream, and a loxP site downstream of the second exon of the targeted gene. Correctly targeted ES cells were injected into recipient blastocysts and chimeric mice were bred with Black Swiss mice (to avoid rescue of the En1 mutant phenotype by the C57BL/6 background). The resulting En1flox-neo mice were then bred to 129 mice constitutively expressing Flp recombinase to remove the Frt-flanked neo cassette, generating En1flox offspring. (J:134516)