Mammary epithelial transplantation. (A) Abdominal mammary gland whole mounts showing mature mammary duct development in 17-week old TG and WT virgin females. The mammary lymph node, a positional landmark, is partially visible (darkly stained body, left end of panel). (B) Diagram illustrating the procedure of mammary epithelial transplantation. Blue oval, mammary fat pad; the ductal tree is represented in purple; small black oval, mammary lymph node; tissue to the left of the vertical line is surgically removed leaving a cleared fat pad. See Methods for details. (C) Left, H&E stained section of the mammary adenocarcinoma and metastatic lung nodule (inset) that arose after transplantation of TG epithelium into the cleared fat pad of a WT host. Tissue was fixed in formalin and embedded in paraffin. Right, DNA was isolated from parallel sections and PCR performed, confirming the presence of the transgene in the tumor (M, markers).