During development, cell fate experiments have determined that growth plate and articular chondrocytes differentiate from two distinct populations of cells. Within the growth plate, Indian hedgehog (Ihh) regulates chondrocyte proliferation and differentiation that involves a feedback loop with the parathyroid hormone related protein (PTHrP). We have generated transgenic mice showing that a deregulation of the hedgehog/PTHrP feedback loop during growth plate development that results in chondrodysplasias and the development of cartilage tumours; however, the role of hedgehog signalling in the differentiation and maintenance of articular chondrocyte progenitors is poorly defined. Through investigation of transgenic mice, we hope to further identify the role of hedgehog, and other signalling pathways, on growth plate and articular cartilage development. Team members: Heather Whetstone and Jason Rockel (Not shown: Claire Hsu and Louisa Ho).