Mammary epithelial stem cells

It has recently been shown that the progeny from a single cell may comprise the epithelial population of a fully developed lactating mammary outgrowth in mice. Serial transplantation of epithelial fragments from this clonally derived gland demonstrates that the subsequently generated outgrowths are also comprised of progeny from the original antecedent. All epithelial cell types were found to be present within these clonal normal populations incl uding luminal, myoepithelial, ductal, and lobule-committed epithelial proge nitors and fully competent mammary epithelial stem cells. These observation s demonstrate the presence of multipotent tissue-specific epithelial stem c ells among the parenchyma of the murine mammary gland. Similarly, genetic a nalysis of contiguous portions of individual human mammary ducts within the same breast indicates their clonal derivation. Here, we discuss the proper ties, location, division-potential, senescence, and plasticity associated w ith mammary epithelial stem cells and present the developing evidence for t heir presence in human breast and their important role in the risk for brea st cancer development. Further, we review the present morphologic and genet ic evidence for the characterization of specific stem cell markers and line age-limited progenitor cells in human and rodent mammary epithelium. Publis hed 2001 Wiley-Liss, Inc.(dagger).