Divergent Expression of , , and Genes During Jawed Vertebrate Cartilage Mineralization.

While cartilage is an ancient tissue found both in protostomes and deuterostomes, its mineralization evolved more recently, within the vertebrate lineage. , , and the members (Secretory Calcium-binding PhosphoProtein genes which evolved from ) are major players of dentine and bone mineralization, but their involvement in the emergence of the vertebrate mineralized cartilage remains unclear. We performed hybridization on mineralizing cartilaginous skeletal elements of the frog () and the shark () to examine the expression of (present in both species), (present in only) and the members (present in only). We show that while mineralizing cartilage expresses (but not ) in , it expresses the genes (but not ) in , and propose two possible evolutionary scenarios to explain these opposite expression patterns. In spite of these genetic divergences, our data draw the attention on an overlooked and evolutionarily conserved peripheral cartilage subdomain expressing or the genes and exhibiting a high propensity to mineralize.