The locations at which joints arise during foetal development are essential for determining the final skeletal pattern and are also strongly implicated in a number of joint diseases. At present little is known about the complicated molecular mechanisms involved in joint formation. In the February Cell, researchers from the Department of Genetics, Harvard Medical School suggest that Wnt-14 is essential in the initial steps of joint formation.

Christine Hartmann and Clifford Tabin studied the early joint-forming regions of the developing chick limb. They found that Wnt-14 shows a striking pattern of expression in the regions of joint formation. Observations of localised Wnt-14 misexpression indicated that cells within prechondrogenic regions respond to exogenous Wnt-14 and become morphologically and histologically distinct from neighbouring cartilage, taking on histological and molecular properties typical of the early joint interzone (Cell 2001, 104:341-351).

But ectopic Wnt-14 expression led to a repression of...