Role of tyrosine kinase in the evolution of multicellular animals

从单细胞原生动物到多细胞动物的进化是动物史上的一个重要事件。为了解决在这一转变中发生的分子事件，我们研究了作为参与动物多细胞行为的关键分子开关的Src酪氨酸激酶的功能变化。从单细胞脊椎动物Monosiga ovata和原始多细胞海绵EPhydatia River viatilis中克隆了Src及其负调控因子CSK的同源基因，并对其活性和调控特性进行了比较分析。这两种生物都含有多种形式的Src，所有的结构域都参与了负调控和一个功能性的CSK。与脊椎动物一样，在河蟹中，多种Src亚型被CSK磷酸化严格抑制。然而，在卵形分枝杆菌中，由于激酶结构域的三级结构的偏差，即使在CSK磷酸化的形式下，Src也保持着强大的活性。用sRc抑制剂抑制后鞭藻中的sRc可促进Poll…丝状结构介导的更分散的集落形成。这些发现表明，Src及其调控成分的出现早于动物起源，但调控系统经历了伴随多细胞进化而来的功能进化。为了阐明Src在多细胞动物中的基础作用，分析了Src在线虫中功能丧失的影响。Src-1基因的突变导致远端尖细胞(DTC)以一种依赖活动的方式指导性腺形态发生。Src-1突变的作用被位于RAC途径的基因突变强烈抑制，这表明SRC-1是RAC途径的上游调节因子，控制细胞骨架重塑。Src-1突变体在神经细胞迁移方面也表现出缺陷。这些发现表明，SRC-1在响应细胞外指导信号方面发挥着不可或缺的作用，这些信号通过控制细胞骨架重塑的途径引导细胞在发育过程中发生迁移。较少

Evolution from unicellular protists to mulicellular animals is a crucial event in animal history. To address the molecular events occurred at this transition, we examined the functional alteration of Src tyrosine kinase, as a key molecular switch involved in the animal multicellularity. Orthologues of Src and its negative regulator Csk were molecular cloned from the unicellular choanoflagellate Monosiga ovata and the primitive multicellular sponge Ephydatia fluviatilis, and their activities and regulatory features were comparatively analyzed. Both organisms contain multiple forms of Src with all the domains involved in negative regulation and a functional Csk. In E.fluviatilis, multiple Src isoforms are stringently inhibited by Csk phosphorylation as in vertebrate. However, in M.ovata, Src retains robust activity even in the Csk phosphorylated form, due to deviations in the tertiary structure of the kinase domain. Inhibition of Src in choanoflagellates by the Src inhibitor promotes pol … More arized colony formation mediated by filopodia-like structures. These findings demonstrate that the appearance of Src and its regulatory components predates animal origins, but the regulatory system underwent a functional evolution accompanying the evolution of multicellularity.To address the fundamental roles Src in the multicellular animals, Effects of loss-of-function of Src in C.elegans was analyzed. A mutation in the src-1 gene resulted in defective distal tip cell (DTC)-directed gonad morphogenesis in an activity dependent manner. The effect of the src-1 mutation was robustly suppressed by mutations in the genes located in a Rac pathway, which suggests that SRC-1 is an upstream regulator of the Rac pathway that controls cytoskeletal remodeling. The src-1 mutant also exhibits defects in neural cell migration. These findings suggest that SRC-1 plays an integral role in responding to the extracellular guidance cues that direct the cell migration occurring during development via a pathway that controls cytoskeletal remodeling. Less