Tooth development in sharks

Teeth and skin denticles, which are flat, hard, tooth-shaped structures, are part of a group of organs called odontodes. The evolutionary origin of teeth and their relationship to other odontode structures remains unclear. Kyle Martin et al. (pp. 14769–14774) compared the cellular and molecular mechanisms that shape the development of teeth and denticles in the catshark (Scyliorhinus canicula), an organism that has maintained both forms of odontodes. Gene expression profiles revealed a remarkable conservation of gene expression patterns during the development of teeth and denticles, suggesting that a shared gene regulatory network drives the development of all odontodes. Genetic studies of developing catshark jaws revealed that the epithelial stem cell marker sox2 is expressed during tooth, but not denticle, development and is associated with the rapid and continuous regenerative capacity of shark teeth. Dendrites do not regenerate and develop only after injury or when they are lost. In addition, the authors found that teeth and anteriormost oral taste buds, which constantly regenerate, emerge from the same field of epithelial sox2+ progenitor cells. According to the authors, truly regenerative teeth may have arisen when the gene regulatory network for producing simple denticles combined with the network for producing the highly regenerative taste buds in the mouth. - Read at PNAS.org