Fetal protection from osteopenia through RU486 administration during late gestation. Mineralized bone is visualized with Alizarin red S and cartilage with alcian blue. A. Tibia and fibula of an E18.5 Lifr +/+ untreated control mouse. Bone mineralization occurs throughout the length of the bone, including the epiphysis. The same can be seen for Lifr +/+ and Lifr +/- mice whether the mother was adrenalectomized on E16.5 of gestation (C) or received RU486 on E16.5 and E17.5 (E). B. An E18.5 Lifr -/- untreated control mouse littermate of the pup shown in A demonstrates mineralized bone loss at the growth plate. D. An E18.5 Lifr -/- littermate of the pup shown in C where the mother was adrenalectomized on E16.5 displays similar bone loss at the epiphysis as seen in B, but bones of the Lifr -/- mice in this group tend to be more fragile and show breaks within areas of osteopenia (arrow). F. A Lifr -/- E18.5 pup that was exposed to RU486 on E16.5 and E17.5. The epiphysis is modestly thinner than that of the wild type littermate (E), but mineralization at the growth plate is improved relative to the untreated control (B) or adrenalectomy treated (D) Lifr -/- pups. The size bar indicates 1 cm.