The carmine alumn stained whole mounts were prepared as described (52 (link)). The fourth inguinal mammary gland were fixed in 10% neutral buffered formalin for paraffin embedding and processed for immunohistochemistry as described (9 (link)). Oil Red O staining of cryosections of mammary glands was performed as described (53 (link)). Stained sections were imaged with a Observer Z1 epifluorescence microscope (Zeiss, Oberkochen, Germany) or with a A1 confocal microsope (Nikon Instruments Inc, Melville, NY).