Figure 2.

Localization of RANK mRNA expression in developing and adult bone by in situ hybridization. Sections of embryonic and adult long bones were hybridized with ³³P-labeled antisense riboprobes to RANK, processed and stained with hematoxylin/eosin. Panels A–E are from fetal (E15.5) femur, with B and D being darkfield images of A and C, respectively. Panels F–I are from adult (6-week) femur, with G being a darkfield image of F. RANK is expressed by multinucleated cells attached to matrix, consistent with osteoclasts in areas of active bone modeling in the fetus and adult. Hypertrophic chondrocytes in the adult growth plate also appear to express RANK transcripts. Arrows mark the position of osteoclasts, whereas arrowheads mark the position of hypertrophic chondrocytes. [Bars = 400 μm (A and F), 100 μm (C), and 25 μm (E and H).]