This is supported by research using Shh-Cre+ mice to specifically express a mutant form of the Kirsten-Ras oncogene homolog with a glycine to asparagine mutation at codon 12 (KRasG12D) in TA cells, which fail to initiate papilloma formation, in contrast to HF-specific expression of the KRasG12D mutant using K15-Cre+ mice, where papillomas frequently manifest [23]. Here, SHH is linked to papilloma.