Exons 3 and 4 were deleted and replaced by a betageo/puro cassette, with only 21 bp of exon 3 remaining. This was confirmed at the genomic and RNA level. The construct contains a premature stop codon in the first 8 bp of the selection cassette, which is predicted to lead to a truncated 206 amino acid protein lacking presumably the immunoglobulin-like (Ig-like), serine-rich, fibronectin III, transmembrane and PDZ-binding domains.