Osteoclast fusion and regulation by RANKL-dependent and independent factors

Figure 1 Receptor activator of NF-κB ligand increases the expression of a set of fusion genes in osteoclasts derived from WT bone marrow cells. Bone marrow mono-nuclear cells were cultured with macrophage colony-stimulating factor for 2 d and were then treated with Receptor activator of NF-κB ligand (RANKL) for additional 3 or 4 d. Cells were harvested at day 0 (before RANKL), day 3 and day 4 after RANKL treatment. A: Tartrate-resistant acid phosphatase (TRAP) staining, osteoclast number and area, and TRAP mRNA expression; B: The expression levels of fusion genes by quantitative polymerase chain reaction. The values are the fold increase vs the value on Day 0 as 1. MFR: Macrophage fusion receptor; DC-STAMP: Dendritic cell-specific transmembrane protein