Holland P W, Garcia-Fernàndez J, Williams N A, Sidow A
Department of Zoology, University of Oxford, UK.
Dev Suppl. 1994:125-33.
All vertebrates possess anatomical features not seen in their closest living relatives, the protochordates (tunicates and amphioxus). Some of these features depend on developmental processes or cellular behaviours that are again unique to vertebrates. We are interested in the genetic changes that may have permitted the origin of these innovations. Gene duplication, followed by functional divergence of new genes, may be one class of mutation that permits major evolutionary change. Here we examine the hypothesis that gene duplication events occurred close to the origin and early radiation of the vertebrates. Genome size comparisons are compatible with the occurrence of duplications close to vertebrate origins; more precise insight comes from cloning and phylogenetic analysis of gene families from amphioxus, tunicates and vertebrates. Comparisons of Hox gene clusters, other homeobox gene families, Wnt genes and insulin-related genes all indicate that there was a major phase of gene duplication close to vertebrate origins, after divergence from the amphioxus lineage; we suggest there was probably a second phase of duplication close to jawed vertebrate origins. From amphioxus and vertebrate homeobox gene expression patterns, we suggest that there are multiple routes by which new genes arising from gene duplication acquire new functions and permit the evolution of developmental innovations.
所有脊椎动物都具有其现存亲缘关系最近的原索动物（被囊动物和文昌鱼）所没有的解剖学特征。其中一些特征依赖于脊椎动物特有的发育过程或细胞行为。我们对可能促成这些创新起源的基因变化感兴趣。基因复制，随后新基因发生功能分化，可能是一类允许重大进化变化的突变。在这里，我们检验这样一种假说，即基因复制事件发生在脊椎动物起源和早期辐射的附近时期。基因组大小比较与接近脊椎动物起源时发生复制的情况相符；更精确的见解来自对文昌鱼、被囊动物和脊椎动物基因家族的克隆和系统发育分析。对Hox基因簇、其他同源异型框基因家族、Wnt基因和胰岛素相关基因的比较均表明，在与文昌鱼谱系分化后，接近脊椎动物起源时存在一个基因复制的主要阶段；我们认为在有颌脊椎动物起源附近可能还存在第二个复制阶段。从文昌鱼和脊椎动物同源异型框基因的表达模式来看，我们认为基因复制产生的新基因通过多种途径获得新功能，并促成发育创新的进化。
