Cell proliferation was reduced in the <i>Twist1^flox/+</i>; <i>Twist2^Cre/+</i> mice.

<p>(A–B) BrdU immunohistochemical staining of the femur sections of 7-day-old control and <i>Twist1^flox/+</i>; <i>Twist2^Cre/+</i> mice. The BrdU-positive cells (signal in brown) were counted in a 100-µm zone of the metaphysis, demarcated by the chondro-osseous junction and the marked line (A), and in the femoral diaphysis (B). The osteoblast/osteoprogenitor proliferation was reduced in both the metaphysis (C) and diaphysis (D) in the <i>Twist1^flox/+</i>; <i>Twist2^Cre/+</i> mice, compared to the control mice (<i>n</i> = 4, *<i>P</i><0.05). The data were expressed as the percentage of BrdU-positive nuclei versus total nuclei. Scale bars: 100 µm.