Bone cells unite

Bone-resorbing osteoclasts can't pull together in the absence of dendritic cell–specific transmembrane protein (DC-STAMP), according to new data from Yagi and colleagues (page 345). Without this receptor, osteoclast precursor cells cannot fuse with one another. The failure to fuse cripples the bone resorbing function of the cells, causing osteopetrosis (increased bone mass).

DC-STAMP is a seven-transmembrane–spanning receptor that was originally isolated from dendritic cells (DCs). The ligand for DC-STAMP and its function on DCs are unknown, but this receptor was recently found on osteoclasts and shown to be required for these cells to develop from their macrophage precursors.

Yagi and colleagues now refine these data by showing that multinucleated osteoclasts were completely absent in the bones of mice lacking DC-STAMP, although osteoclast development was intact. The DC-STAMP–deficient mice...