Stat3 is required to maintain the multipotency of mammary stem cells and their proliferative potential.

<p>(A) Whole mount staining of mammary outgrowths originating from CD24⁺ CD49f^hi basal cells sorted from mammary glands of 5-week-old <i>Stat3^fl/fl,K14-Cre⁻</i> and <i>Stat3^fl/fl;K14-Cre⁺</i> females. (B) Limiting dilution analysis to assess the repopulating frequency of the mammary stem cell-enriched population sorted from mammary glands of 5-week-old <i>Stat3^fl/fl,K14-Cre⁻</i> and <i>Stat3^fl/fl;K14-Cre⁺</i> females. Number of outgrowths per number of transplanted fat pads and percentage of fat pad filled ± standard error of the mean are shown. CI: confidence interval. (C) H&E staining of mammary outgrowths originating from CD24⁺ CD49f^hi basal cells sorted from mammary glands of 5-week-old <i>Stat3^fl/fl;K14-Cre⁻</i> and <i>Stat3^fl/fl;K14-Cre⁺</i> females. (D, E) Immunohistochemistry staining for pStat5 (red, D), Ki67 (red, E) and E-cadherin (green) in mammary outgrowths originating from CD24⁺ CD49f^hi cells from mammary glands of 5-week-old <i>Stat3^fl/fl,K14-Cre⁻</i> and <i>Stat3^fl/fl;K14-Cre⁺</i> females. Nuclei were stained with Hoechst 33342 (blue).