Phylogeny of Echinoderm Hemoglobins.

Ana B Christensen,Dean C Semmens,Xavier Bailly,Daniel Janies,David Hoogewijs,Serge N Vinogradov,Kord M Kober,Joseph L Herman,Gregorio Linchangco,Maurice R Elphick

doi:10.1371/journal.pone.0129668

Abstract

BackgroundRecent 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.ResultsThe 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.ConclusionThe 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.

Highlights

Genomic information accrued over the last decade has demonstrated the existence of globins in all three kingdoms of life [1], far beyond the familiar myoglobin (Mb) and αand β-globins, it has unexpectedly expanded the repertory of vertebrate globins
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, to assess the hypothesis that the neuroglobin and cytoglobin lineages are present in echinoderms
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

Summary

Introduction

Genomic information accrued over the last decade has demonstrated the existence of globins in all three kingdoms of life [1], far beyond the familiar myoglobin (Mb) and αand β-globins, it has unexpectedly expanded the repertory of vertebrate globins. Molecular phylogenetic analyses of vertebrate globins agree that GbX is closely related to Ngbs, while Cygbs are related to cyclostome hemoglobins (Hbs), Mb, GbE, GbY and the Hb α- and β-globins [13,14,15,16,17]. 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. 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, to assess the hypothesis that the neuroglobin and cytoglobin lineages are present in echinoderms

Methods

Results

Conclusion