A cassette containing lacZ and neo genes was inserted into exon 2. The construct was designed such that a fusion protein, containing the alternatively spliced exon 1 and lacZ product, would be produced. The insertion deleted the majority of exon 2 and all of exon 3, which encode residues conserved in the FGF family. Transcript was undetected via Northern blot analysis of total cerebellar RNA obtained from homozygous mutant mice. While in situ hybridization and RNA blot analysis showed similar mRNA expression patterns between the mutant and endogenous alleles, protein expression patterns were shown to vary via X-gal staining.