Increased bone resorption in Krox20^+/− animals. (A) Histologic images showing increased osteoclast number and thinner trabeculae in the distal femur of WT (left) and Krox20^+/− (right) animals. Arrows point at TRAP⁺ lining osteoclasts. Images were acquired using a Zeiss Axioskop, with a 40× objective and a SPOT digital camera. (B) Oc.N/BS, TRAP⁺ lining osteoclasts relative to bone surface measured in histologic sections of the distal femur from five 8-week-old mice per group. (C) Serum CTX levels in 4 WT and 3 Krox20^+/− 6-week-old mice. (D) FACS analysis of CD115⁺ monocytes in the distal femoral metaphysis of 4 WT (left) and 5 Krox20^+/− (right) 6-week-old mice. Bars show the percentage CD115⁺ monocytes from total red blood cell-free bone marrow cells. (E-G) Parameters of bone formation were measured in histologic sections of the distal femur from 5 8-week-old mice per group. (E) MAR indicates mineral apposition rate. (F) Min.Peri indicates mineralizing perimeter. (G) BFR indicates bone formation rate. Bars are mean ± SEM with the Krox20^+/− values always on the right. *P < .05 compared with WT controls.