PETERKOVA, R*; LESOT, H; PETERKA , M; Institute of Experimental Medicine Academy of Sciences, Prague, Czech Republic.; INSERM U595, Strasbourg, France; Institute of Experimental Medicine Academy of Sciences, Prague, Czech Republic: Phylogenetic memory of developing mammalian dentition

During evolution, the origin of new structures was often accompanied by the suppression of old ones. Primordia of some suppressed structures had been integrated in the new context. Suppressed structures can be retraced due to atavisms and vestiges. Atavism is an exceptional emergence of an ancestral form in a present individual. In contrast, vestige of an ancestral structure regularly occurs during ontogenesis in all members of an actual species. The vestigial structures have practical importance, because they represent integral part of development. Some of them can play important role during normal or pathological morphogenesis. Vestigial structures occur also during dentition development in the laboratory mouse. In the incisive and diastema regions, dental placodes are transiently distinct being morphologically similar to the early tooth primordia in reptiles. These placodes are eliminated by apoptosis in the prospective toothless diastema, while they combine together in the incisive region and give commonly rise to a gnawing incisor. Large vestigial tooth buds occur in front of the molars. They have been homologized to the premolars that disappeared during mouse evolution. The distal premolar vestige becomes incorporated into the first molar germ and participates in development of its mesial part. This incorporation suggests the mechanism of disappearance of the most distal premolar during mouse evolution. Devious development of tooth vestiges can cause some dental anomalies observed in mutant mice. Supernumerary incisor or molar in mutant mice might originate from the revivification of the vestigial ancestral tooth primordia.