A PGK-neomycin resistance cassette replaced part of exon 1 and all of exons 2 and 3. Northern analysis of poly(A)+ RNA using a probe that corresponds to exon 3 did not detect transcript in homozygous mutant whole E14.5 embryo. In situ RNA hybridization did not detect gene expression in the gut of E14.5 homozygous mutant embryos. (J:29443)