title: Phylogeny of Echinoderm Hemoglobins.
abstract: BACKGROUND
  Recent genomic information has revealed that neuroglobin and cytoglobin are the two principal lineages of vertebrate hemoglobins, with the latter encompassing the familiar myoglobin and α-globin/β-globin tetramer hemoglobin, and several minor groups. In contrast, very little is known about hemoglobins in echinoderms, a phylum of exclusively marine organisms closely related to vertebrates, beyond the presence of coelomic hemoglobins in sea cucumbers and brittle stars. We identified about 50 hemoglobins in sea urchin, starfish and sea cucumber genomes and transcriptomes, and used Bayesian inference to carry out a molecular phylogenetic analysis of their relationship to vertebrate sequences, specifically, to assess the hypothesis that the neuroglobin and cytoglobin lineages are also present in echinoderms.
  
  
  RESULTS
  The genome of the sea urchin Strongylocentrotus purpuratus encodes several hemoglobins, including a unique chimeric 14-domain globin, 2 androglobin isoforms and a unique single androglobin domain protein. Other strongylocentrotid genomes appear to have similar repertoires of globin genes. We carried out molecular phylogenetic analyses of 52 hemoglobins identified in sea urchin, brittle star and sea cucumber genomes and transcriptomes, using different multiple sequence alignment methods coupled with Bayesian and maximum likelihood approaches. The results demonstrate that there are two major globin lineages in echinoderms, which are related to the vertebrate neuroglobin and cytoglobin lineages. Furthermore, the brittle star and sea cucumber coelomic hemoglobins appear to have evolved independently from the cytoglobin lineage, similar to the evolution of erythroid oxygen binding globins in cyclostomes and vertebrates.
  
  
  CONCLUSIONS
  The presence of echinoderm globins related to the vertebrate neuroglobin and cytoglobin lineages suggests that the split between neuroglobins and cytoglobins occurred in the deuterostome ancestor shared by echinoderms and vertebrates.
authors.affiliation: Biology Department, Lamar University, Beaumont, Texas, United States of America.
authors.forename: Ana B
authors.initials: AB
authors.lastname: Christensen
authors.affiliation: Department of Statistics, University of Oxford, Oxford, OX1 3TG, United Kingdom; Division of Mathematical Biology, National Institute of Medical Research, London, NW7 1AA, United Kingdom.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Herman
authors.affiliation: School of Biological & Chemical Sciences, Queen Mary University of London, London E1 4NS, United Kingdom.
authors.forename: Maurice R
authors.initials: MR
authors.lastname: Elphick
authors.affiliation: Department of Ecology & Evolutionary Biology, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Kord M
authors.initials: KM
authors.lastname: Kober
authors.affiliation: College of Computing and Informatics, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, United States of America.
authors.forename: Daniel
authors.initials: D
authors.lastname: Janies
authors.affiliation: College of Computing and Informatics, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, United States of America.
authors.forename: Gregorio
authors.initials: G
authors.lastname: Linchangco
authors.affiliation: School of Biological & Chemical Sciences, Queen Mary University of London, London E1 4NS, United Kingdom.
authors.forename: Dean C
authors.initials: DC
authors.lastname: Semmens
authors.affiliation: Marine Plants and Biomolecules, Station Biologique de Roscoff, 2968 Roscoff, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Bailly
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University School of Medicine, Detroit, Michigan 48201, United States of America.
authors.forename: Serge N
authors.initials: SN
authors.lastname: Vinogradov
authors.affiliation: Institute of Physiology, University of Duisburg-Essen, Essen, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Hoogewijs
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D000078842:Cytoglobin; D004447:Echinodermata / Q000737:chemistry / Q000235:genetics*; D005914:Globins / Q000737:chemistry / Q000235:genetics*; D016013:Likelihood Functions; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics*; D000078787:Neuroglobin; D010802:Phylogeny; D011487:Protein Conformation
chemical_list: D000078842:Cytoglobin; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D005914:Globins