Opazo Juan C, Lee Alison P, Hoffmann Federico G, Toloza-Villalobos Jessica, Burmester Thorsten, Venkatesh Byrappa, Storz Jay F
Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile
Institute of Molecular and Cell Biology, Comparative and Medical Genomics Laboratory, Agency for Science, Technology, and Research Biopolis, Singapore
Mol Biol Evol. 2015 Jul;32(7):1684-94. doi: 10.1093/molbev/msv054. Epub 2015 Mar 4.
Comparative analyses of vertebrate genomes continue to uncover a surprising diversity of genes in the globin gene superfamily, some of which have very restricted phyletic distributions despite their antiquity. Genomic analysis of the globin gene repertoire of cartilaginous fish (Chondrichthyes) should be especially informative about the duplicative origins and ancestral functions of vertebrate globins, as divergence between Chondrichthyes and bony vertebrates represents the most basal split within the jawed vertebrates. Here, we report a comparative genomic analysis of the vertebrate globin gene family that includes the complete globin gene repertoire of the elephant shark (Callorhinchus milii). Using genomic sequence data from representatives of all major vertebrate classes, integrated analyses of conserved synteny and phylogenetic relationships revealed that the last common ancestor of vertebrates possessed a repertoire of at least seven globin genes: single copies of androglobin and neuroglobin, four paralogous copies of globin X, and the single-copy progenitor of the entire set of vertebrate-specific globins. Combined with expression data, the genomic inventory of elephant shark globins yielded four especially surprising findings: 1) there is no trace of the neuroglobin gene (a highly conserved gene that is present in all other jawed vertebrates that have been examined to date), 2) myoglobin is highly expressed in heart, but not in skeletal muscle (reflecting a possible ancestral condition in vertebrates with single-circuit circulatory systems), 3) elephant shark possesses two highly divergent globin X paralogs, one of which is preferentially expressed in gonads, and 4) elephant shark possesses two structurally distinct α-globin paralogs, one of which is preferentially expressed in the brain. Expression profiles of elephant shark globin genes reveal distinct specializations of function relative to orthologs in bony vertebrates and suggest hypotheses about ancestral functions of vertebrate globins.
对脊椎动物基因组的比较分析不断揭示出珠蛋白基因超家族中令人惊讶的基因多样性，其中一些基因尽管起源古老，但系统发育分布却非常有限。软骨鱼（板鳃亚纲）珠蛋白基因库的基因组分析对于了解脊椎动物珠蛋白的复制起源和祖先功能应该特别有帮助，因为板鳃亚纲和硬骨脊椎动物之间的分化代表了有颌脊椎动物中最基部的分支。在这里，我们报告了对脊椎动物珠蛋白基因家族的比较基因组分析，其中包括姥鲨（Callorhinchus milii）完整的珠蛋白基因库。利用所有主要脊椎动物类群代表的基因组序列数据，对保守共线性和系统发育关系的综合分析表明，脊椎动物的最后一个共同祖先拥有至少七个珠蛋白基因：雄激素球蛋白和神经球蛋白的单拷贝、珠蛋白X的四个旁系同源拷贝，以及整个脊椎动物特异性珠蛋白集合的单拷贝祖先。结合表达数据，姥鲨珠蛋白的基因组清单产生了四个特别令人惊讶的发现：1）没有神经球蛋白基因的踪迹（这是一个高度保守的基因，在迄今为止已检测的所有其他有颌脊椎动物中都存在），2）肌红蛋白在心脏中高度表达，但在骨骼肌中不表达（这反映了具有单循环系统的脊椎动物可能的祖先状况），3）姥鲨拥有两个高度分化的珠蛋白X旁系同源物，其中一个在性腺中优先表达，4）姥鲨拥有两个结构不同的α-珠蛋白旁系同源物，其中一个在大脑中优先表达。姥鲨珠蛋白基因的表达谱揭示了相对于硬骨脊椎动物直系同源物的不同功能特化，并提出了关于脊椎动物珠蛋白祖先功能的假设。
