WNT proteins drive the development and maintenance of many tissues, including bone. It is less clear which of the many WNT proteins act on bone or where these WNTs act in the skeleton; however, loss-of-function mutations in WNT1 cause bone fragility in children and adults. In this issue of the JCI, Joeng and colleagues demonstrate that bone formation is under the control of WNT1 produced by osteocytes, the cells that reside deep in the bone matrix and form dendritic networks. The implication of WNT1 in the control of bone formation identifies a potential new target for the treatment of low bone mass disorders, such as osteoporosis.
