Exons 3 and 4 of the targeted gene were replaced with a construct containing: loxP-FRT-polyA-neomycin (in reverse transcriptional orientation)-FRT-exons 3-9 of Pofut2 mini cDNA-polyA-loxP-Stop-mCherry-polyA. Flp-mediated recombination removed the FRT-flanked neo cassette. mCherry fluorescence is not detectable in this allele. Cre-mediated recombination removed the loxP-flanked exons 3-9. In-situ hybridization and H&E staining indicates that embryos fail to express markers of extra-embryonic ectoderm and mesoderm differentiation. (J:234992)