Convergent evolution of hemoglobin switching in jawed and jawless vertebrates

Rohlfing et al. BMC Evolutionary Biology (2016) 16:30 DOI 10.1186/s12862-016-0597-0 RESEARCH ARTICLE Open Access Convergent evolution of hemoglobin switching in jawed and jawless vertebrates Kim Rohlfing1, Friederike Stuhlmann1, Margaret F. Docker2 and Thorsten Burmester1* 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. Conclusion: 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. Keywords: Agnatha, Ammocoete, Gene family, Hemoglobin switching, Myoglobin, Ontogeny, Oxygen, Phylogeny Background Hemoglobin (Hb) is a respiratory protein that facilitates the transport of oxygen (O2) from the respiratory surfaces (usually the skin, gills or lungs) to the inner organs [1]. Hb is present in almost all vertebrates, except some icefish species [2]. It is member of the globin protein family that is characterized by a conserved fold that includes a heme prosthetic group, by which the proteins reversibly bind O2 [1, 3]. In addition to Hb, other types of globins are present in the jawed vertebrates (Gnathostomata): myoglobin (Mb) [4], neuroglobin (Ngb) [5], cytoglobin (Cygb) [6–8], globin E (GbE) [9], globin X (GbX) [10], globin Y (GbY) [11] and androglobin (Adgb) [12]. A variety of functions other than O2 supply have been associated with these globins, including detoxification of reactive oxygen and nitrogen species (ROS/RNS) or signaling (for review, see [13]). * Correspondence: 1 Institute of Zoology, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany Full list of author information is available at the end of the article The Hb of the jawed vertebrates is a hetero-tetramer that is composed of two α- and two β-chains. The interaction of the chains leads to cooperative O2 binding [3]. Further modulation of the O2 affinity according to the physiological requirements is brought about by the interaction with organic phosphates (ATP, GTP, 2,3-diphosphoglycerate), CO2, and protons (Bohr effect), or by changing temperatures. Multiple, paralogous α- and β-genes have originated in evolution by gene duplication and divergence. During ontogeny, the O2 demand changes and, consequently, in many vertebrates distinct Hb chains are expressed in certain developmental stages [11, 14, 15]. For example, humans possess six Hb genes (α, β, γ, δ, ε, and ζ) [1]. Their differential expression results in embryonic, fetal, and adult forms of hemoglobin tetramers [1, 16]. The embryonic Hb consists of two α or ζ chains, respectively, plus two ε chains; the fetal Hb is composed of two α and two γ chains, which change to the adult Hb form (2 × α, 2 × β) during the first year after birth [1]. © 2016 Rohlfing et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Rohlfing et al. BMC Evolutionary Biology (2016) 16:30 Embryonic and fetal Hb have higher oxygen affinities than adult Hb, which is essential to overcome the placental barrier in mammals [17]. The lamprey harbors five distinct globins: Adgb, GbX and Cygb, and functionally analogous Hbs and Mbs that evolved convergently from a common globin ancestor [18]. Lampreys, along with hagfishes, constitute the cyclostomes, the sole survivors of a lineage that diverged from the ancestor to the jawed vertebrates more than 500 million years ago [19, 20]. Like its counterpart in the jawed vertebrates, the lamprey Mb (aMb) is preferentially expressed in the skeletal muscle and presumably supports O2 to this tissue. The agnathan Hb (aHb) is structurally distinct from the gnathostome Hb, although it carries out similar functions. aHb is a monomer in its oxygenated form and associates into homodimers or tetramers when deoxygenated [21, 22]. Like the gnathostome Hbs, aHbs display cooperative O2 binding and a pH-dependent regulation of O2 affinity [23]. In the sea lamprey Petromyzon marinus, four distinct chains have been identified on the protein level that are components of the adult aHb [24–27]. However, analysis of the P. marinus genome revealed at least 14 additional aHb genes plus two pseudogenes [18]. Four of these closely resemble the known adult chains and probably are recent gene duplicates that cannot be distinguished from the main chain on the protein level. The expression patterns of the other nine aHbs remain unclear, leading to the speculation that they represent globin chains expressed in early developmental stages [18]. Sea lampreys (P. marinus) spend most of their life as filter-feeding larvae (ammocoetes), burrowed in the sediments of freshwater rivers [28]. After a dramatic metamorphosis involving major modifications to the morphology, physiology and behavior of the animal [29], the adult anadromous lampreys migrate to the sea, where they have a free-swimming hematophagous lifestyle. At the completion of the feeding phase, lampreys become sexually mature and return to fresh water, undergoing an upstream migration prior to spawning and death. Early electrophoretic studies reported a shift from larval (...truncated)