title: Conserved intron positions in FGFR genes reflect the modular structure of FGFR and reveal stepwise addition of domains to an already complex ancestral FGFR.
abstract: We have analyzed the evolution of fibroblast growth factor receptor (FGFR) tyrosine kinase genes throughout a wide range of animal phyla. No evidence for an FGFR gene was found in Porifera, but we tentatively identified an FGFR gene in the placozoan Trichoplax adhaerens. The gene encodes a protein with three immunoglobulin-like domains, a single-pass transmembrane, and a split tyrosine kinase domain. By superimposing intron positions of 20 FGFR genes from Placozoa, Cnidaria, Protostomia, and Deuterostomia over the respective protein domain structure, we identified ten ancestral introns and three conserved intron groups. Our analysis shows (1) that the position of ancestral introns correlates to the modular structure of FGFRs, (2) that the acidic domain very likely evolved in the last common ancestor of triploblasts, (3) that splicing of IgIII was enabled by a triploblast-specific insertion, and (4) that IgI is subject to substantial loss or duplication particularly in quickly evolving genomes. Moreover, intron positions in the catalytic domain of FGFRs map to the borders of protein subdomains highly conserved in other serine/threonine kinases. Nevertheless, these introns were introduced in metazoan receptor tyrosine kinases exclusively. Our data support the view that protein evolution dating back to the Cambrian explosion took place in such a short time window that only subtle changes in the domain structure are detectable in extant representatives of animal phyla. We propose that the first multidomain FGFR originated in the last common ancestor of Placozoa, Cnidaria, and Bilateria. Additional domains were introduced mainly in the ancestor of triploblasts and in the Ecdysozoa.
authors.affiliation: FB 17, Morphology and Evolution of Invertebrates, Philipps Universitaet Marburg, Karl von Frisch Str. 8, 35032, Marburg, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Rebscher
authors.forename: Christina
authors.initials: C
authors.lastname: Deichmann
authors.forename: Stefanie
authors.initials: S
authors.lastname: Sudhop
authors.forename: Jens Holger
authors.initials: JH
authors.lastname: Fritzenwanker
authors.forename: Stephen
authors.initials: S
authors.lastname: Green
authors.forename: Monika
authors.initials: M
authors.lastname: Hassel
mesh_terms: D000818:Animals; D003063:Cnidaria / Q000235:genetics; D019143:Evolution, Molecular; D006829:Hydra / Q000235:genetics*; D054909:Placozoa / Q000235:genetics*; D017434:Protein Structure, Tertiary; D017468:Receptors, Fibroblast Growth Factor / Q000737:chemistry / Q000235:genetics*
chemical_list: D017468:Receptors, Fibroblast Growth Factor