Globin-X (GbX) is an enigmatic member of the vertebrate globin gene family with a wide phyletic distribution that spans protostomes and deuterostomes. Unlike canonical globins such as hemoglobins and myoglobins, functional data suggest that GbX does not have a primary respiratory function. Instead, evidence suggests that the monomeric, membrane-bound GbX may play a role in cellular signaling or protection against the oxidation of membrane lipids. Recently released genomes from key vertebrates provide an excellent opportunity to address questions about the early stages of the evolution of GbX in vertebrates. We integrate bioinformatics, synteny, and phylogenetic analyses to characterize the diversity of GbX genes in nonteleost ray-finned fishes, resolve relationships between the GbX genes of cartilaginous fish and bony vertebrates, and demonstrate that the GbX genes of cyclostomes and gnathostomes derive from independent duplications. Our study highlights the role that whole-genome duplications (WGDs) have played in expanding the repertoire of genes in vertebrate genomes. Our results indicate that GbX paralogs have a remarkably high rate of retention following WGDs relative to other globin genes and provide an evolutionary framework for interpreting results of experiments that examine functional properties of GbX and patterns of tissue-specific expression. By identifying GbX paralogs that are products of different WGDs, our results can guide the design of experimental work to explore whether gene duplicates that originate via WGDs have evolved novel functional properties or expression profiles relative to singleton or tandemly duplicated copies of GbX.

中文翻译：

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脊椎动物 Globin-X 基因的全基因组复制和多样化

Globin-X (GbX) 是脊椎动物珠蛋白基因家族的一个神秘成员，具有广泛的系统分布，涵盖原口动物和后口动物。与血红蛋白和肌红蛋白等典型球蛋白不同，功能数据表明 GbX 不具有主要呼吸功能。相反，有证据表明单体膜结合 GbX 可能在细胞信号传导或防止膜脂氧化方面发挥作用。最近发布的关键脊椎动物基因组为解决有关脊椎动物 GbX 进化早期阶段的问题提供了绝佳的机会。我们综合生物信息学、同线性和系统发育分析来表征非硬骨鱼射线鳍鱼类 GbX 基因的多样性，解析软骨鱼和骨脊椎动物的 GbX 基因之间的关系，并证明圆口类和颌口类的 GbX 基因源自独立重复。我们的研究强调了全基因组重复（WGD）在扩大脊椎动物基因组中的基因库中所发挥的作用。我们的结果表明，与其他珠蛋白基因相比，GbX 旁系同源物在 WGD 后具有非常高的保留率，并为解释检查 GbX 功能特性和组织特异性表达模式的实验结果提供了一个进化框架。通过识别不同 WGD 产物的 GbX 旁系同源物，我们的结果可以指导实验工作的设计，以探索源自 WGD 的基因重复相对于 GbX 的单拷贝或串联重复拷贝是否进化出新的功能特性或表达谱。