CD24 and CD49f expressions of E14.5 mouse mammary anlagen cells define putative distribution of earlier embryonic mammary stem cell activities.

Stem cell biology offers promise for understanding the origins of the mammary gland. However, the distribution of mammary stem cell (MaSC) activities at earlier embryonic stages has not been fully identified. The markers for sorting adult MaSC, CD24, CD29, and CD49f have been applied to analyze fetal MaSCs. Here we explored mammary anlagen MaSCs by investigating the expression of CD24 and CD49f. According to the comparative analysis between adult mammary gland and fetal mammary anlagen, we found that fetal mouse mammary anlagen may possess a high percentage of potential MaSCs. Flow cytometry analysis revealed 2 distinct mammary anlagen populations: Lin ^- CD24 ^med and Lin ^- CD24 ^high . Sphere-forming and mammary repopulating assays confirmed that the stem cell activity of E14.5 mouse mammary anlagen was restricted to the Lin ^- CD24 ^med cell population. Furthermore, CD24 ^med mammary anlagen cells were separated into Lin ^- CD24 ^med CD49f ⁺ and Lin ^- CD24 ^med CD49f ^- populations and identified, respectively. The results proved that the mammary anlagen Lin ^- CD24 ^med CD49f ⁺ cell population possesses more stem cell activities than the Lin ^- CD24 ^med CD49f ^- cell population. However, a limited numbers of stem cells and large numbers of stromal cells were identified in mammary anlagen in the Lin ^- CD24 ^med cell population.