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Updated: Aug 14, 2026
Mouse Mammary Epithelial Cells form Mammospheres During Lactogenic Differentiation
Published on: October 6, 2009
An improved definition of mouse mammary epithelial side population cells
M J Smalley1, I Titley, A Ashworth
1The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK.
Background:
Mammary epithelial side population cells have been suggested as candidate mammary stem cells. To date, for technical reasons, these cells have been poorly defined and cross-comparison of data between different laboratories has been difficult. Here, we set out to define mammary side population cells in a way that improves the ability to carry out such comparisons.
Methods:
Mouse mammary epithelial cells were stained with Hoechst 33342. Light scatter, PI staining and clonogenicity of different regions of the Hoechst profile were examined. Time-course analyzes of Hoechst 33342 loading were carried out.
Results:
Detailed examination of the light scatter and PI staining of Hoechst 33342-stained mammary cells enabled single live side population and non-side population cells to be defined with greater accuracy. Comparison of ABC pump inhibitors identified potential discrepancies in results obtained using these inhibitors. Time-course analyzes enabled side populations cells to be identified as a dynamic cell population that could be defined accurately by using the relationship between Hoechst 33342-staining profiles of consecutive time points.
Discussion:
Defining the side population of solid tissues as a 'stabilized side population percentage' will enable a more rigorous study of the side population phenomenon and improve evaluation of results from different laboratories.
