Investigating deeper into the physiological relevance of this temporal change, we added a creERT2 transgene under the control of the SBE-driven reporter and, on the basis of tamoxifen-activated lineage-tracing, we found that, even though the TGFβ-reporter-positive cells were infrequent in papillomas, they contributed substantially to SCCs (Extended Data Fig. 1c). The gene discussed is TGFB1; the disease is papilloma.