Discovery and evolution of novel hemerythrin genes in annelid worms

Abstract

BackgroundDespite extensive study on hemoglobins and hemocyanins, little is known about hemerythrin (Hr) evolutionary history. Four subgroups of Hrs have been documented, including: circulating Hr (cHr), myohemerythrin (myoHr), ovohemerythrin (ovoHr), and neurohemerythrin (nHr). Annelids have the greatest diversity of oxygen carrying proteins among animals and are the only phylum in which all Hr subgroups have been documented. To examine Hr diversity in annelids and to further understand evolution of Hrs, we employed approaches to survey annelid transcriptomes in silico.ResultsSequences of 214 putative Hr genes were identified from 44 annelid species in 40 different families and Bayesian inference revealed two major clades with strong statistical support. Notably, the topology of the Hr gene tree did not mirror the phylogeny of Annelida as presently understood, and we found evidence of extensive Hr gene duplication and loss in annelids. Gene tree topology supported monophyly of cHrs and a myoHr clade that included nHrs sequences, indicating these designations are functional rather than evolutionary.ConclusionsThe presence of several cHrs in early branching taxa suggests that a variety of Hrs were present in the common ancestor of extant annelids. Although our analysis was limited to expressed-coding regions, our findings demonstrate a greater diversity of Hrs among annelids than previously reported.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0933-z) contains supplementary material, which is available to authorized users.

Broad Phylogenetic Occurrence of the Oxygen-Binding Hemerythrins in Bilaterians

“…3 , orange and gray clades). As expected ( Costa-Paiva etal. 2017 ), leech “nHr” was strongly supported ( P = 1) as sister lineage to a myoHr sequence from the same species.…”

“…We found Hr orthologs in 12 additional annelid species ( table 1 ), augmenting previous counts ( Bailly etal. 2008 ; Costa-Paiva etal. 2017 ).…”

“…All new 58 sequences possessed the five-residue insertion before the D α-helix characteristic of myoHrs ( Bailly etal. 2008 ; Costa-Paiva etal. 2017 ) ( fig.…”

“…However more recent work ( Vanin etal. 2006 ; Costa-Paiva etal. 2017 ) has confirmed that there are only two types of Hrs (myoHr and cHr).…”

“…Recent studies show that occurrence, diversity, and expression of Hrs in animals is much greater than currently recorded ( Martín-Durán etal. 2013 ; Costa-Paiva etal. 2017 ).…”