The evolutionary transition from invertebrates to vertebrates involved extensive gene duplication, but understanding precisely how such duplications contributed to this transition requires more detailed knowledge of specific cases of genes and gene families. Myogenic differentiation (MyoD) has long been recognized as a master developmental control gene and member of the MyoD family of bHLH transcription factors (myogenic regulatory factors [MRFs]) that drive myogenesis across the bilaterians. Phylogenetic reconstructions within this gene family are complicated by multiple instances of gene duplication and loss in several lineages. Following two rounds of whole-genome duplication (2R WGD) at the origin of the vertebrates, the ancestral function of MRFs is thought to have become partitioned among the daughter genes, so that MyoD and Myf5 act early in myogenic determination, whereas Myog and Myf6 are expressed later, in differentiating myoblasts. Comparing chordate MRFs, we find an independent expansion of MRFs in the invertebrate chordate amphioxus, with evidence for a parallel instance of subfunctionalization relative to that of vertebrates. Conserved synteny between chordate MRF loci supports the 2R WGD events as a major force in shaping the evolution of vertebrate MRFs. We also resolve vertebrate MRF complements and organization, finding a new type of vertebrate MRF gene in the process, which allowed us to infer an ancestral two-gene state in the vertebrates corresponding to the early- and late-acting types of MRFs. This necessitates a revision of previous conclusions about the simple one-to-four origin of vertebrate MRFs.

中文翻译：

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通过2R超过一比四：MyoD相关的肌肉调节因子（MRFs）的独立的两栖类扩张和两个基因的祖先脊椎动物状态的证据。

从无脊椎动物到脊椎动物的进化过渡涉及广泛的基因复制，但是要准确地了解此类复制是如何促成这种过渡的，则需要对基因和基因家族的具体情况有更详细的了解。肌源性分化（MyoD）长期以来一直被认为是主要的发育控制基因和MyoD的成员bHLH转录因子（肌源性调节因子[MRF]）家族，在整个Bilaterians中推动肌发生。该基因家族内的系统发育重建由于基因复制的多个实例和几个谱系的丢失而变得复杂。在脊椎动物起源处进行了两轮全基因组复制（2R WGD）之后，MRF的祖先功能被认为已在子代基因之间分配，因此MyoD和Myf5在成肌测定中起早期作用，而Myog和Myf6稍后在分化成肌细胞中表达。比较脊索动物的MRFs，我们发现无脊椎动物脊索动物的两栖动物中的MRFs有一个独立的扩展，并且有证据表明与脊椎动物相比，亚功能化的情况平行。氯酸盐MRF基因座之间的保守同构支持2R WGD事件，这是塑造脊椎动物MRF进化的主要力量。我们还解决了脊椎动物MRF的补体和组织问题，在此过程中发现了一种新型的脊椎动物MRF基因，这使我们能够推断出与MRF早期和晚期类型相对应的脊椎动物的祖先两个基因状态。这需要修订关于脊椎动物MRF的简单的一到四起源的先前结论。