title: Convergent evolution of hemoglobin switching in jawed and jawless vertebrates.
abstract: BACKGROUND
  During development, humans and other jawed vertebrates (Gnathostomata) express distinct hemoglobin genes, resulting in different hemoglobin tetramers. Embryonic and fetal hemoglobin have higher oxygen affinities than the adult hemoglobin, sustaining the oxygen demand of the developing organism. Little is known about the expression of hemoglobins during development of jawless vertebrates (Agnatha).
  
  
  RESULTS
  We identified three hemoglobin switches in the life cycle of the sea lamprey. Three hemoglobin genes are specifically expressed in the embryo, four genes in the filter feeding larva (ammocoete), and nine genes correspond to the adult hemoglobin chains. During the development from the parasitic to the reproductive adult, the composition of hemoglobin changes again, with a massive increase of chain aHb1. A single hemoglobin chain is expressed constitutively in all stages. We further showed the differential expression of other globin genes: Myoglobin 1 is most highly expressed in the reproductive adult, myoglobin 2 expression peaks in the larva. Globin X1 is restricted to the embryo; globin X2 was only found in the reproductive adult. Cytoglobin is expressed at low levels throughout the life cycle.
  
  
  CONCLUSIONS
  Because the hemoglobins of jawed and jawless vertebrates evolved independently from a common globin ancestor, hemoglobin switching must also have evolved convergently in these taxa. Notably, the ontogeny of sea lamprey hemoglobins essentially recapitulates their phylogeny, with the embryonic hemoglobins emerging first, followed by the evolution of larval and adult hemoglobins.
authors.affiliation: Institute of Zoology, University of Hamburg, Martin-Luther-King-Platz 3, D-20146, Hamburg, Germany. kim.rohlfing@uni-hamburg.de.
authors.forename: Kim
authors.initials: K
authors.lastname: Rohlfing
authors.affiliation: Institute of Zoology, University of Hamburg, Martin-Luther-King-Platz 3, D-20146, Hamburg, Germany. fstuhlmann@gmail.com.
authors.forename: Friederike
authors.initials: F
authors.lastname: Stuhlmann
authors.affiliation: Department of Biological Sciences, University of Manitoba, 50 Sifton Road, Winnipeg, MB, R3T 2N2, Canada. margaret.docker@umanitoba.ca.
authors.forename: Margaret F
authors.initials: MF
authors.lastname: Docker
authors.affiliation: Institute of Zoology, University of Hamburg, Martin-Luther-King-Platz 3, D-20146, Hamburg, Germany. thorsten.burmester@uni-hamburg.de.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Burmester
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D006454:Hemoglobins / Q000235:genetics*; D048428:Petromyzon / Q000235:genetics / Q000254:growth & development; D010802:Phylogeny; D014714:Vertebrates / Q000145:classification / Q000235:genetics* / Q000254:growth & development
chemical_list: D006454:Hemoglobins
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