Figure 1.

Stem cell model for the organization of the prostate epithelium. The prostate epithelial compartment is organized in a hierarchy of expanding stem cell units. There are a limited number of androgen-independent basal stem cells that, in dividing, create new basal stem cells as well as giving rise to a larger subset of androgen-sensitive amplifying basal cells. In the absence of androgen (as in the castrated prostate) the amplifying cells are in a steady-state with the rate of proliferation equal to the rate of cell death. If androgen is present, the majority of these androgen-sensitive amplifying cells differentiate into androgen-dependent transit glandular epithelial cells. Once the normal number of these androgen-dependent glandular cells is reached, the cell proliferation rate balances the cell death rate such that neither prostatic regression nor continuous glandular overgrowth occurs. Because of the clonally expansive nature of this hierarchical stem cell organization, the vast majority of the epithelial compartment is composed of androgen-dependent glandular cells, with lower numbers of androgen-sensitive basal cells and a limited number of androgen-independent basal stem cells.