Abstract
BackgroundDuring 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).ResultsWe 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.ConclusionBecause 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0597-0) contains supplementary material, which is available to authorized users.
Highlights
During development, humans and other jawed vertebrates (Gnathostomata) express distinct hemoglobin genes, resulting in different hemoglobin tetramers
In addition to Hb, other types of globins are present in the jawed vertebrates (Gnathostomata): myoglobin (Mb) [4], neuroglobin (Ngb) [5], cytoglobin (Cygb) [6,7,8], globin E (GbE) [9], globin X (GbX) [10], globin Y (GbY) [11] and androglobin (Adgb) [12]
Expression pattern of agnathan Hb (aHb) during development We quantified the mRNA levels of the aHb genes of the sea lamprey (P. marinus) in different developmental stages by RNA-seq and Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR)
Summary
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. 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]. 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]
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