Fig. 1

Preparation of ‘Confetti’ Mice. a The “confetti mouse” is an engineered mouse strain carrying the Confetti cassette comprising short cDNA sequences that encode 4 different fluorescent proteins, separated by “LoxP” sites that enable cutting by the enzyme Cre-recombinase. The cassette is inserted into the ROSA locus under the control if the strong CAGG promoter. Activation of Cre-recombinase with Tamoxifen results in cutting of the DNA at the LoxP sites in a random manner, resulting in labelling of each cell with one of the 4 colors shown. b Fluorescent image of a benign papilloma one week after activation of the Cre-recombinase, showing labelling of each cell with one of the 4 colors. Confetti mice were initially treated using a standard protocol for inducing the growth of squamous tumors which results in the development of benign papillomas on the skin after about 10-15 weeks. At this stage the mice are treated with Tamoxifen, resulting in activation of a single fluorescent color in each individual cell. This picture was taken 1 week later, at which point some of the individual cells had already divided, giving rise to small clusters of cells with the same color