The skeleton: no bones about it

The skeleton is composed of bone and cartilage. These tissues are made of an exquisite assembly of functionally distinct cell populations and are required to support the structural, biochemical and mechanical integrity of the skeleton. The functions of the skeleton, which include its role in growth, locomotion, ion homeostasis and the protection of vital organs, are fundamental to the healthy organism. Development, growth and maintenance of the skeleton is under complex endocrine and genetic control and depends on a tight integration of cellular events within the skeleton and within the systems that deliver and accumulate mineral for hydroxyapatite formation (Karsenty 2003).

With few exceptions, bone formation is dependent on the development of the cartilage anlagen from mesenchymal precursors. These cartilage models of the future bones are replaced by bone through endochondral ossification, a process also responsible for linear bone growth at the epiphyseal plate during pre- and post-natal life (Kronenberg 2003). In essence, the laying down of a cartilage matrix by the chondrocyte, the primary cell type of cartilage, is a pre-requisite for future bone modelling and remodelling by the osteoblast and osteoclast. To fully appreciate the contribution of both cartilage and bone elements to skeletal physiology (and pathology), it is essential that we more thoroughly understand the molecular events …