Irimia Manuel, Maeso Ignacio, Garcia-Fernàndez Jordi
Mol Biol Evol. 2008 Aug;25(8):1521-5. doi: 10.1093/molbev/msn109. Epub 2008 May 9.
Vertebrate and Drosophila Iroquois genes are organized in clusters of 3 genes sharing blocks of conserved regulatory sequences. Here, we report a 3-gene cluster in the basal, preduplicative chordate amphioxus. Surprisingly, however, the origin of the amphioxus cluster is independent of those in vertebrates and drosophilids. Investigation of genomic organization of Iroquois genes in other 17 metazoan genomes revealed a fourth independent 3-gene cluster organization in polychaetes, as well as additional 2- and 4-gene clusters in other clades, in one of the most striking examples of convergence in genomic organization described so far. The recurrent independent evolution of Iroquois clusters suggests a functional importance of this organization for these genes, perhaps related to the sharing of regulatory elements. Consistent with this, comparative analysis of genomic regions flanking the 3 amphioxus Irx genes revealed several blocks of sequences, conserved for at least 100 Myr. Finally, we discuss the possible causes and implications of the convergent evolution of this genomic and regulatory organization throughout metazoans.
脊椎动物和果蝇的Iroquois基因以3个基因的簇形式组织在一起，这些基因共享保守调控序列块。在此，我们报告了基部、复制前的脊索动物文昌鱼中的一个3基因簇。然而，令人惊讶的是，文昌鱼基因簇的起源独立于脊椎动物和果蝇中的基因簇。对其他17种后生动物基因组中Iroquois基因的基因组组织进行研究发现，多毛纲动物中有第四个独立的3基因簇组织，以及其他进化枝中的额外2基因和4基因簇，这是迄今为止所描述的基因组组织趋同的最显著例子之一。Iroquois基因簇的反复独立进化表明这种组织对这些基因具有功能重要性，可能与调控元件的共享有关。与此一致的是，对文昌鱼3个Irx基因侧翼基因组区域的比较分析揭示了几个至少保守1亿年的序列块。最后，我们讨论了整个后生动物中这种基因组和调控组织趋同进化的可能原因及影响。
