title: The molecular phylogeny of eph receptors and ephrin ligands.
abstract: BACKGROUND
  The tissue distributions and functions of Eph receptors and their ephrin ligands have been well studied, however less is known about their evolutionary history. We have undertaken a phylogenetic analysis of Eph receptors and ephrins from a number of invertebrate and vertebrate species.
  
  
  RESULTS
  Our findings indicate that Eph receptors form three major clades: one comprised of non-chordate and cephalochordate Eph receptors, a second comprised of urochordate Eph receptors, and a third comprised of vertebrate Eph receptors. Ephrins, on the other hand, fall into either a clade made up of the non-chordate and cephalochordate ephrins plus the urochordate and vertebrate ephrin-Bs or a clade made up of the urochordate and vertebrate ephrin-As.
  
  
  CONCLUSIONS
  We have concluded that Eph receptors and ephrins diverged into A and B-types at different points in their evolutionary history, such that primitive chordates likely possessed an ancestral ephrin-A and an ancestral ephrin-B, but only a single Eph receptor. Furthermore, ephrin-As appear to have arisen in the common ancestor of urochordates and vertebrates, whereas ephrin-Bs have a more ancient bilaterian origin. Ancestral ephrin-B-like ligands had transmembrane domains; as GPI anchors appear to have arisen or been lost at least 3 times.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, Victoria, Canada. dan.mellott@gmail.com
authors.forename: Dan O
authors.initials: DO
authors.lastname: Mellott
authors.forename: Robert D
authors.initials: RD
authors.lastname: Burke
mesh_terms: D000818:Animals; D001665:Binding Sites; D002450:Cell Communication; D036342:Ephrins / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D008024:Ligands; D016013:Likelihood Functions; D009432:Neural Crest / Q000196:embryology / Q000378:metabolism*; D010802:Phylogeny; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D020239:Receptor Cross-Talk; D036081:Receptors, Eph Family / Q000235:genetics*; D016415:Sequence Alignment; D017421:Sequence Analysis; D014561:Urochordata; D014714:Vertebrates
chemical_list: D036342:Ephrins; D008024:Ligands; D011505:Protein-Tyrosine Kinases; D036081:Receptors, Eph Family