Supplementary Figure Legends Supplementary Figure 1. Characterization of neoplasms of the prostate epithelium in p53PE-/-; RbPE-/- mice. Double immunofluorescence staining was performed on paraffin sections of prostate tumor. Majority of tumor cells express both cytokeratin 8 (CK8, A, green) and synaptophysin (SYN, B, red). C, DAPI counterstaining. D, Merged image of A-C. Cells co-expressing cytokertin 8 and synaptophysin are yellow. Majority of tumor cells also co-express synaptophysin (SYN, E, green) and androgen receptor (AR, F, red). G, DAPI counterstaining. H, Merged image of E- G. Calibration bar, A-H, 100 μm. Supplementary Figure 2. PCR analysis of Rb and p53 gene structure in prostate tumor stroma cells in p53PE-/-; RbPE-/- mice. A-D, H&E-stained prostate sections from p53PE-/-; RbPE-/- mice are shown before (A, C) and after (B, D) microdissection performed as described by us earlier (Genes Dev.10: 1870-1879, 1996). Arrows indicate the stroma regions from which cells were isolated. Calibration bar: A-D, 100 μm. E, PCR analysis of Rb and p53 gene structure in six independent tumor stroma (lanes S1-S6) collected by microdissection, normal wild-type prostate stroma cells (lane WT) and cells homozygous for both floxed Rb and p53 genes (lane L/L). Lane M, DNA marker. 295-, 269-, and 247-bp fragments are diagnostic for floxed, excised, and wild type alleles of the Rb gene, respectively. 316-, 198-, and 163-bp fragments are diagnostic for floxed, excised, and wild-type alleles of the p53 gene, respectively.