Developmental control of chondrogenesis and osteogenesis

During vertebrate embryogenesis, bones of the vertebral column, pelvis, and upper and lower limbs, are formed on an initial cartilaginous model. This process, called endochondral ossification, is characterized by a precise se ries of events such as aggregation and differentiation of mesenchymal cells , and proliferation, hypertrophy and death of chondrocytes. Bone formation initiates in the collar surrounding the hypertrophic cartilage core that is eventually invaded by blood vessels and replaced by bone tissue and bone m arrow. Over the last years we have extensively investigated cellular and mo lecular events leading to cartilage and bone formation. This has been parti ally accomplished by using a cell culture model developed in our laboratory . In several cases observations have been confirmed or directly made in the developing embryonic bone of normal and genetically modified chick and mou se embryos. In this article we will review our work in this field.