title: Amphioxus FGF signaling predicts the acquisition of vertebrate morphological traits.
abstract: FGF signaling is one of the few cell-cell signaling pathways conserved among all metazoans. The diversity of FGF gene content among different phyla suggests that evolution of FGF signaling may have participated in generating the current variety of animal forms. Vertebrates possess the greatest number of FGF genes, the functional evolution of which may have been implicated in the acquisition of vertebrate-specific morphological traits. In this study, we have investigated the roles of the FGF signal during embryogenesis of the cephalochordate amphioxus, the best proxy for the chordate ancestor. We first isolate the full FGF gene complement and determine the evolutionary relationships between amphioxus and vertebrate FGFs via phylogenetic and synteny conservation analysis. Using pharmacological treatments, we inhibit the FGF signaling pathway in amphioxus embryos in different time windows. Our results show that the requirement for FGF signaling during gastrulation is a conserved character among chordates, whereas this signal is not necessary for neural induction in amphioxus, in contrast to what is known in vertebrates. We also show that FGF signal, acting through the MAPK pathway, is necessary for the formation of the most anterior somites in amphioxus, whereas more posterior somite formation is not FGF-dependent. This result leads us to propose that modification of the FGF signal function in the anterior paraxial mesoderm in an amphioxus-like vertebrate ancestor might have contributed to the loss of segmentation in the preotic paraxial mesoderm of the vertebrate head.
authors.affiliation: Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7232, Université Pierre et Marie Curie Paris 06, Observatoire Océanologique, F-66651 Banyuls-sur-Mer, France.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bertrand
authors.forename: Alain
authors.initials: A
authors.lastname: Camasses
authors.forename: Ildiko
authors.initials: I
authors.lastname: Somorjai
authors.forename: Mohamed R
authors.initials: MR
authors.lastname: Belgacem
authors.forename: Olivier
authors.initials: O
authors.lastname: Chabrol
authors.forename: Marie-Line
authors.initials: ML
authors.lastname: Escande
authors.forename: Pierre
authors.initials: P
authors.lastname: Pontarotti
authors.forename: Hector
authors.initials: H
authors.lastname: Escriva
mesh_terms: D000818:Animals; D005075:Biological Evolution; D043344:Chordata / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D019143:Evolution, Molecular; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D005775:Gastrula; D006801:Humans; D020935:MAP Kinase Signaling System; D008954:Models, Biological; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D019170:Somites
chemical_list: D005346:Fibroblast Growth Factors