Since p53 ablation has been frequently observed in BCC and other tumors, which could possibly speed up the process of BCC (Rady et al., 1992; Soussi & Béroud, 2001; Soussi et al., 2000; Wijnhoven et al., 2005), we constructed lentiviral expressing shRNAs targeting tree shrew p53 with tdTomato expression driven by an individual PGK promoter, which was used to follow the shRNA expressing cells and tissues (Figure 4A). The gene discussed is TP53; the disease is skin basal cell carcinoma.