Capacity of mammary fat pads of adult C3H/HeMs mice to interact morphogenetically with fetal mammary epithelium.

When rudimentary mammary epithelium from 13- to 17-day female C3H/HeMs fetuses was transplanted into gland-free mammary fat pads of 3-week-old mice, organogenetic development of the grafts occurred, resembling that seen in normal mammary gland morphogenesis. Initial developmental growth did not require the reproductive hormones. Mammary fat pads of juvenile (3-wk-old), young adult (8- to 12-wk-old), and fully matured (40-wk-old) females had equal ability to interact morphogenetically with fetal mammary epithelium. Fetal pulmonary, pancreatic, and salivary gland epithella showed no morphogenetic response within adult mammary fat. An exception was rudimentary hair follicle epithellum, which underwent extensive development toward hair follicles within mammary fat. Mammary glands that developed from rudimentary mammary epithellum transplanted into gland-free fat pads underwent morphologic changes characteristic of lactation when the hosts bore young.