Dentition development and budding morphogenesis

The development of functional teeth in the mouse has been widely used as a model to study general mechanisms of organogenesis. Compared with other mam mals, in which three incisors, one canine, four premolars, and three molars may occur even in each dental quadrant, the mouse functional dentition is strongly reduced. It comprises only one incisor separated from three molars by a toothless gap diastema - at the location of the missing teeth. Howeve r, mouse embryos also develop transient vestigial dental primordia between the incisor and molar germs in both the upper and lower jaws. These rudimen tal structures regress, and epithelial apoptosis is involved in this proces s. The existence of the vestigial dental structures allowed a better assess ment of the periodicity in the mouse dentition, which extends opportunities for the interpretation of molecular data on tooth development. We compared the dentition development with tentative models of budding morphogenesis i n other epithelial appendages lungs and feathers. We suggested how developm ental control by signaling molecules, including bone morphogenetic protein (Bmp), sonic hedgehog (Shh), and fibroblast growth factor (Fgf), can be sim ilarly involved during budding morphogenesis of dentition and other epithel ial appendages, We propose that epithelial apoptosis plays an important rol e in achieving specific features of dentition, whose development involves b oth budding and its more complex variant branching. The failure of segregat ion of the originating buds supports the participation of the concrescence of several tooth primordia in the evolutionary differentiation of mammalian teeth.