Acide rétinoïque et diversité des patrons dentaires chez les poissons téléostéens – BOUILLABAISSE

A major objective of current research in zoology and evolutionary sciences is to understand the molecular basis of natural diversity. A powerful approach to identifying the developmental genetic basis of morphological adaptations is the comparison of a model organism in which the genetic control of the development of the feature of interest is well understood, and a series of ''satellite'' organisms of varied and known degrees of relationship. In vertebrates teeth are extremely interesting as these structures exhibit tremendous diversity in size, shape, number and structure, both within and among organisms. In this project we propose to use the Cypriniformes, a highly diverse group of freshwater fishes containing more than 3400 species including the most popular fish model, the zebrafish, Danio rerio to better delineate understand the developmental basis of teeth diversity. Cypriniforme teeth have two main characteristics that render their study particularly interesting from an evolutionary and developmental perspective: (i) they exhibit only pharyngeal teeth since they have lost the oral teeth and the developmental basis for this well characterized event of loss is still unknown; (ii) they harbor a large diversity of tooth patterns and it has been proposed that a persistent trend of reduction in tooth number arose during Cypriniformes diversification. Once again the developmental basis of this reduction and more generally of the teeth diversity of Cypriniformes are not known. Recent experiments from the coordinator lab have shown that retinoic acid signaling is necessary at very precisely defined time windows for the induction of teeth in zebrafish. This effect of retinoic acid is reminiscent of its classical effect as a molecule allowing the definition of temporal windows of competence during development. It is easy to imagine how subtle heterochronic changes in these windows can provide an elegant evolutionary basis for phenotypic variation at various taxonomic levels. In this project we propose to explore how variations in the retinoic acid (RA) pathway may have played a role in the appearance of the distinct tooth pattern common to all Cypriniformes (that is the loss of oral teeth) as well as in the diversification of tooth patterns inside Cypriniformes. For this, we will take advantage of the wide diversity of tooth patterns present in the model species, zebrafish as well as in « satellite » species of Cypriniformes. We propose an integrated series of developmental, genomic, evolutionary and morphological approaches that will allow exploring the notion that RA may have played a role on the evolution of tooth pattern at several developmental and evolutionary contexts. We will specifically ask the question whether changes in RA signaling pathway have played a role in the loss of oral teeth in Cypriniformes. In addition, at a smaller taxonomic level we plan to test if RA signaling has played a role in the morphological diversification of tooth rows that is observed in Cypriniformes. By using Cypriniformes, including the zebrafish as an experimental model system, we will ask three specific questions: 1) Is RA effectively implicated in oral tooth loss in Cypriniformes' 2) Is RA signaling implicated in tooth row organization and tooth shape in zebrafish' 3) Is RA implicated in tooth diversification in Cypriniformes'