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Journal of Biomedicine and Biotechnology
Volume 1 (2001), Issue 3, Pages 133-143
Correspondence article

Identification of Stem Cell Units in the Terminal End Bud and Duct of the Mouse Mammary Gland

1Department of Biological Sciences, Hampton University, Hampton 23668, VA, USA
2Center of Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda 20892, MD, USA

Copyright © 2001 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The mouse mammary gland may undergo cycles of proliferation, terminal differentiation, tissue remodeling, and more importantly malignant transformation.Mammary epithelial stem cells and their progeny participate in these processes.Mammary epithelial stem cells are multipotent, exhibit properties of self renewal (up to 7 divisions)and may exist either as long-lived nondividing cells or as proliferating-differentiating cells. The focus of this study was to locate stem cells by identifying them as long-lived, label-retaining mammary epithelial cells (LRCs)in growth active (developing)or growth static (aged)mammar y ducts. Initially, primary epithelial cells were pulse labeled with either fluorescent tracker dye and/or BrdU. Cells were then transplanted into cleared juvenile syngeneic mammary fat pads and held for 5weeks or 8weeks. In this study, we demonstrate that LRCs are stem cells and their progeny (transitional cells)ar e arranged as transitional units (TUs). Additionally, TUs are located every 250 ± 75 µm in ducts or in the terminal end bud 200–600 µm in diameter. Molecules expressed in TUs were Zonula Occludens-1 and α-catenin proteins which were significantly detected in 75%–91% (P < 0.001)of the LRCs cells that make up the TU. These data suggest that transitional units may be a group of label-retaining stem cells and maybe involved in the developmental or cancer process.