Assay of Tumor Initiating Cell (TIC) frequencies for basal and luminal cell subpopulations from Wnt-induced tumors.

Cell fractions purified by flow cytometry were assayed by isograft to mammary fat pads at limiting dilutions. We assume that if the significance of the goodness of fit calculation is >0.05, TIC frequencies can be calculated from limiting cell dilutions (the pGOF are shown below the TIC frequency; the goodness of fit calculation is done according to the limdil software, see Methods). Pairwise comparison of the sub-fractions of cells shows that the TIC frequency in the luminal and basal cells is significantly different (* p = 1.06×10−5), as was the TIC frequency for basal and total (Lin−) cells (** p = 2.7×10−4). To determine the absolute number of TICs in each fraction, the number of TICs per million total cells was calculated as the product of the number of cells in that subfraction, and the calculated TIC frequency. Fold enrichment is shown as the frequency of TICs in basal or luminal cells/frequency of TICs in the total population.