Institute of Zoology, Biocenter Grindel, University of Hamburg, Germany.
Teaching Hospital Cologne, University of Cologne, Cologne, Germany.
Genome Biol Evol. 2021 Jul 6;13(7). doi: 10.1093/gbe/evab078.
The members of the globin superfamily are a classical model system to investigate gene evolution and their fates as well as the diversity of protein function. One of the best-known globins is myoglobin (Mb), which is mainly expressed in heart muscle and transports oxygen from the sarcolemma to the mitochondria. Most vertebrates harbor a single copy of the myoglobin gene, but some fish species have multiple myoglobin genes. Phylogenetic analyses indicate an independent emergence of multiple myoglobin genes, whereby the origin is mostly the last common ancestor of each order. By analyzing different transcriptome data sets, we found at least 15 multiple myoglobin genes in the polypterid gray bichir (Polypterus senegalus) and reedfish (Erpetoichthys calabaricus). In reedfish, the myoglobin genes are expressed in a broad range of tissues but show very different expression values. In contrast, the Mb genes of the gray bichir show a rather scattered expression pattern; only a few Mb genes were found expressed in the analyzed tissues. Both, gray bichir and reedfish possess lungs which enable them to inhabit shallow and swampy waters throughout tropical Africa with frequently fluctuating and low oxygen concentrations. The myoglobin repertoire probably reflects the molecular adaptation to these conditions. The sequence divergence, the substitution rate, and the different expression pattern of multiple myoglobin genes in gray bichir and reedfish imply different functions, probably through sub- and neofunctionalization during evolution.
球蛋白超家族的成员是研究基因进化及其命运以及蛋白质功能多样性的经典模式系统。众所周知的球蛋白之一是肌红蛋白（Mb），它主要在心肌中表达，将氧气从肌膜运输到线粒体。大多数脊椎动物只含有一个肌红蛋白基因，但有些鱼类有多个肌红蛋白基因。系统发育分析表明，多个肌红蛋白基因的独立出现，其起源主要是每个目最后的共同祖先。通过分析不同的转录组数据集，我们在多鳍鱼（Polypterus senegalus）和雷鱼（Erpetoichthys calabaricus）中发现了至少 15 个肌红蛋白基因。在雷鱼中，肌红蛋白基因在广泛的组织中表达，但表达值非常不同。相比之下，灰鲟的 Mb 基因表现出相当分散的表达模式；仅在分析的组织中发现了少数 Mb 基因表达。灰鲟和雷鱼都有肺，这使它们能够栖息在整个热带非洲的浅水和沼泽水域，那里的氧气浓度经常波动且较低。肌红蛋白库可能反映了对这些条件的分子适应。灰鲟和雷鱼中多个肌红蛋白基因的序列分歧、替代率和不同的表达模式表明存在不同的功能，可能是通过进化过程中的亚功能化和新功能化。
