An FRT-flanked neomycin resistance cassette was inserted into intron 2. loxP sites were inserted to flank exons 1 and 2. RT-PCR and sequencing revealed the presence of alternatively spliced forms resulting from the splicing of paired box-containing exon 2 to the 3' region of the Pgk1 promoter. With the neo coding region in frame with exon 2 of Pax9, translation of the mRNA predicts and aberrant fusion protein containing the paired domain and the full-length neomycin phosphotransferase, but lacking most of the C-terminal of Pax9. (J:104121)