Rescue of Embryonic Epithelium Reveals That the Homozygous Deletion of the Retinoblastoma Gene Confers Growth Factor Independence and Immortality but Does Not Influence Epithelial Differentiation or Tissue Morphogenesis*

The ability to rescue viable prostate precursor tissue from retinoblastoma-deficient (Rb−/−) fetal mice has allowed for the isolation and characterization of the first Rb−/− prostate epithelial cell line. This cell line, designated Rb−/−PrE, was utilized for experiments examining the consequences of Rb loss on an epithelial population. These findings demonstrated that Rb deletion has no discernible effect on prostatic histodifferentiation in Rb−/−PrE cultures. When Rb−/−PrE cells were recombined with embryonic rat urogenital mesenchyme and implanted into athymic male, nude mouse hosts, the recombinants developed into fully differentiated and morphologically normal prostate tissue. The Rb−/−PrE phenotype was characterized by serum independence in culture and immortality in vivo, when compared with wild type controls. Cell cycle analysis revealed elevated S phase DNA content accompanied by increased expression of cyclin E1 and proliferating cell nuclear antigen. Rb−/−PrE cultures also exhibited a diminished ability to growth arrest under high density culture conditions. We believe that the development of Rb−/− prostate tissue and cell lines has provided a unique experimental platform with which to investigate the consequences of Rb deletion in epithelial cells under various physiological conditions. Additionally, the development of this technology will allow similar studies in other tissues and cell populations rescued from Rb−/− fetuses.