Osteocyte messages from a bony tomb.

Until recently, osteocytes have escaped the limelight, embedded within their cave-like lacunae in the mineralized matrix of bone. In this issue of Cell Metabolism, Tatsumi et al. (2007) present evidence that this "third bone cell" can send either inhibitory signals to osteoclasts to maintain bone mass with normal loading or stimulatory signals to osteoclasts to initiate bone loss upon immobilization, thereby playing an indispensable role in skeletal homeostasis.