Fig. 4. Increased mammary stem cell (MaSC) frequency and regenerative potential in aged p66Shc^−/− mammospheres.

A Outgrowths obtained by limiting-dilution transplantation of M2-mammosphere cell suspensions. MaSC frequencies were calculated with ELDA [71] and indicated. Scale bar = 1 mm; arrow-head: injection site. B Frequencies of outgrowths obtained by transplantation of ∼1 MaSC (same experiment as in A), categorized according to the percentage of repopulated area (<25%, 25–60% and >60%) and analyzed by pairwise Chi-square test; ^*: P = 0.03; ^**: P = 0.008. C Representation in semi-logarithmic axis of sphere forming efficiency upon serial re-plating of mammary epithelial cells from aged (left) and young (right) WT or p66Shc^−/− mice. Data are represented as mean ± SEM of three independent experiments. Statistical analysis: differences at each passage are calculated by two-way ANOVA and Tukey post-hoc test; ^***: P < 0.001. Differences between fit-lines are calculated by simple linear regression after transformation of exponential curves into straight lines; P values are indicated. DR: decrease rate; R²: coefficient of determination.