Costa-Paiva Elisa M, Whelan Nathan V, Waits Damien S, Santos Scott R, Schrago Carlos G, Halanych Kenneth M
Departamento de Genética, Laboratório de Biologia Evolutiva Teórica e Aplicada, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Department of Biological Sciences, Molette Biology Laboratory for Environmental and Climate Change Studies, Auburn University, Auburn, AL, 36849, USA.
BMC Evol Biol. 2017 Mar 23;17(1):85. doi: 10.1186/s12862-017-0933-z.
Despite 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.
Sequences 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.
The 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.
尽管对血红蛋白和血蓝蛋白进行了广泛研究，但关于蚯蚓血红蛋白（Hr）的进化历史却知之甚少。已记录了Hr的四个亚组，包括：循环型Hr（cHr）、肌蚯蚓血红蛋白（myoHr）、卵蚯蚓血红蛋白（ovoHr）和神经蚯蚓血红蛋白（nHr）。环节动物拥有动物界中种类最多的携氧蛋白，并且是唯一记录了所有Hr亚组的门。为了研究环节动物中Hr的多样性并进一步了解Hr的进化，我们采用了在计算机上调查环节动物转录组的方法。
从40个不同科的44种环节动物中鉴定出214个假定的Hr基因序列，贝叶斯推断揭示了两个得到有力统计支持的主要进化枝。值得注意的是，Hr基因树的拓扑结构并不反映目前所理解的环节动物系统发育，并且我们发现环节动物中存在广泛的Hr基因复制和丢失的证据。基因树拓扑结构支持cHr的单系性以及包括nHr序列的一个myoHr进化枝，这表明这些分类是功能性的而非进化性的。
早期分支类群中存在几种cHr，这表明现存环节动物的共同祖先中存在多种Hr。尽管我们的分析仅限于表达的编码区域，但我们的研究结果表明环节动物中Hr的多样性比以前报道的要大。
