A neomycin resistance cassette replaced a genomic fragment containing exons 3 and 4, which encode three disulfide loops, the heparin binding region and the transmembrane domain of the precursor protein. Northern blot analysis on RNA derived from stomach and skin of homozygous mice demonstrated that a smaller transcript is produced from this allele. RT-PCR and sequencing analysis confirmed the loss of coding sequences from this transcript. (J:54980)