Wnt-signaling in skeletal development.

As the vertebrate skeleton develops it progresses from a solely cartilaginous scaffold to a mineralized bony skeleton. The cells that build up the skeleton, the chondrocytes and osteoblasts, are primarily of mesodermal origin. Yet, some facial bones, as well as the endocranium, are derived from neural crest cells. The differentiation of the mesenchymal cells to skeletal precursors as well as their subsequent differentiation and maturation along the two lineages, chondrogenic and osteogenic, is controlled by various different signaling pathways, among them Wnt-signaling. WNTs comprise a family of 19 secreted cysteine-rich glycoproteins and can signal through a variety of different intracellular pathways. Genetic loss- and gain-of-function experiments of Wnt-signaling pathway genes have helped to uncover their multiple roles in skeletogenesis, which will be discussed in this article primarily focusing on endochondral bone formation.