Stromal DNA synthesis is stimulated by young, but not serially aged, mouse mammary epithelium

Ductal elongation in young, proliferating mouse mammary gland is associated with a zone of DNA synthesis in stroma surrounding the end buds. In contrast, slowly growing, serially aged tissue fails to elicit a significant elevation of stromal DNA synthetic activity. Since fatty stroma is required for normal mammary growth and morphogenesis, this altered interaction may be a significant factor in the aging of mammary epithelium.