PATTERNING OF THE MAMMALIAN DENTITION IN DEVELOPMENT AND EVOLUTION

The mammalian dentition is a segmented organ system with shape differe nces among its serially homologous elements (individual teeth). It is believed to have evolved from simpler precursors with greater similari ties in shape among teeth, and a wealth of descriptive data exist on c hanges to the dentition that have occurred within mammals. Recent prog ress has been made in determining the genetic basis of the processes t hat form an individual tooth, but patterning of the dentition as a who le (i.e, the number, location and shape of the teeth) is less well und erstood. In contrast to similarly organized systems, such as the verte bral column and limb, Hox genes are not involved in specifying differe nces among elements. Nevertheless, recent work on a variety of systems is providing clues to the transcription factors and extracellular sig nalling molecules involved.