GFP fluorescence monitors ductal and alveolar development in WOC and during mammary gland transplantation. (A-D) Mammary glands were cultured in IPAH media for a total of 10 days. On days 0 (A), 3 (B), 7 (C), and 10 (D) the mammary glands were briefly removed from the incubator to examine alveolar development as visualized with GFP expression. (E-L) Mammary glands from newborn mice expressing GFP were transplanted into nude mice. E and F show the newborn mammary gland pre-transplantation GFP and H&E imaging, respectively. Post-transplantation in a non-pregnant nude mouse (G-I) allows for visualization of ductal development of the transplanted gland as it grows to fill its fat pad whereas transplantation from a pregnant nude mouse (J-L) causes the transplant to display lobular development characteristic of late pregnancy. GFP images: G and H (higher power) and J and K (higher power), Whole mount images: I and L. Arrows: mammary ducts, thick arrows: lobules, ^: nipple. Magnifications are as indicated.