Approximately 4.4kb of sequence was replaced by a PGK-neo selection cassette. The deleted region contained the promoter and all but 24 base pairs of exon 1. While transcript was undetected by RT-PCR analysis in homozygous mutant mice, Northern blot analysis of total retinal RNA showed the presence of a truncated transcript containing the PGK-neo transgene and the untargeted exons. Immunocytochemistry showed the absence of protein in homozygous mutant mice. Western blot analysis confirmed the staining results as well as verified the lack of protein produced from the truncated transcript.