Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7232, Université Pierre et Marie Curie Paris 06, Observatoire Océanologique, F-66651 Banyuls-sur-Mer, France.
Proc Natl Acad Sci U S A. 2011 May 31;108(22):9160-5. doi: 10.1073/pnas.1014235108. Epub 2011 May 12.
FGF signaling is one of the few cell-cell signaling pathways conserved among all metazoans. The diversity of FGF gene content among different phyla suggests that evolution of FGF signaling may have participated in generating the current variety of animal forms. Vertebrates possess the greatest number of FGF genes, the functional evolution of which may have been implicated in the acquisition of vertebrate-specific morphological traits. In this study, we have investigated the roles of the FGF signal during embryogenesis of the cephalochordate amphioxus, the best proxy for the chordate ancestor. We first isolate the full FGF gene complement and determine the evolutionary relationships between amphioxus and vertebrate FGFs via phylogenetic and synteny conservation analysis. Using pharmacological treatments, we inhibit the FGF signaling pathway in amphioxus embryos in different time windows. Our results show that the requirement for FGF signaling during gastrulation is a conserved character among chordates, whereas this signal is not necessary for neural induction in amphioxus, in contrast to what is known in vertebrates. We also show that FGF signal, acting through the MAPK pathway, is necessary for the formation of the most anterior somites in amphioxus, whereas more posterior somite formation is not FGF-dependent. This result leads us to propose that modification of the FGF signal function in the anterior paraxial mesoderm in an amphioxus-like vertebrate ancestor might have contributed to the loss of segmentation in the preotic paraxial mesoderm of the vertebrate head.
FGF 信号通路是所有后生动物中保守的细胞间信号通路之一。不同门动物中 FGF 基因含量的多样性表明，FGF 信号的进化可能参与了动物形态的多样性的产生。脊椎动物拥有最多数量的 FGF 基因，其功能进化可能与脊椎动物特有的形态特征的获得有关。在这项研究中，我们研究了 FGF 信号在头索动物文昌鱼胚胎发生过程中的作用，文昌鱼是脊索动物祖先的最佳代表。我们首先分离了完整的 FGF 基因库，并通过系统发育和基因共线性保守性分析确定了文昌鱼和脊椎动物 FGF 之间的进化关系。通过药理学处理，我们在文昌鱼胚胎的不同时间窗抑制 FGF 信号通路。我们的结果表明，在原肠胚形成过程中 FGF 信号的需求是脊索动物之间的保守特征，而与脊椎动物中已知的情况相反，在文昌鱼中，该信号对于神经诱导不是必需的。我们还表明，FGF 信号通过 MAPK 通路作用，对于文昌鱼头最前部体节的形成是必需的，而对于更后部体节的形成则不是 FGF 依赖性的。这一结果使我们提出，在文昌鱼样的脊椎动物祖先的前轴旁中胚层中，FGF 信号功能的修饰可能导致了脊椎动物头部前耳轴旁中胚层的分节丢失。
