Tissue-Specific Detection and Expression of Deleted Apc Alleles (A) Tissue-specific genotyping PCR. Only genomic DNA samples from the skin (S) and thymus (T), but not liver (L) of mice positive for K14-cre show the presence of deleted ApcΔ580 allele. (B) Genotype- and tissue-specific expression of the truncated Apc transcripts. A representative gel of RT-PCR using primers F546 and R721, showing that only RNA from the skin and thymus but not liver of mice positive for K14-cre have transcripts from both wild-type (528 bp) and deleted (313 bp) Apc alleles.