CDKN2A and neoplasm: Levels of the p16-3MR transgene were elevated in the tumor (GFP+) cells compared with the surrounding parenchyma (GFP−) cells, similar to p16Ink4a expression, suggesting that in our model p16-3MR expression followed the same trend as the endogenous expression of p16Ink4a (Supplementary Fig. 2a).