Role of tyrosine kinase in the evolution of multicellular animals

酪氨酸激酶Src家族在调节多细胞动物特有的细胞功能中起着关键作用，包括细胞-细胞相互作用、细胞-底物黏附和细胞迁移。为了研究从单细胞祖先向多细胞动物进化过程中Src激酶的功能变化，我们对单细胞脊索鞭毛虫Monosiga ovata和原始多细胞海绵EPhydatia fluviatilis的Src同源物进行了鉴定。在这里，我们证明了src基因家族及其C端的Src激酶(CSK)介导的调控系统已经在单细胞卵形杆菌中建立，并且这种Src相对于多细胞的Src具有独特的特征：它可以被CSK在负调控位点磷酸化，但即使以磷酸化的形式仍然表现出大量的活性。对卵形分枝杆菌和河流分枝杆菌同源基因之间嵌合体分子的分析表明，激活域的结构变化是导致…的原因对卵形分枝杆菌更为低效的负调控。当在脊椎动物成纤维细胞中表达时，无论是否存在CSK，卵形分枝杆菌Src都可以诱导细胞转化。这些发现表明，在单细胞卵形线虫中，稳定的CSK介导的负调控所需的Src结构仍然不成熟，并且稳定的Src负调控的发展可能与动物多细胞的进化有关。为了阐明Src在多细胞动物中的基本作用，分析了线虫中Src功能丧失的影响。在这里，我们证明了SRC-1，SFK的同源基因，在引导秀丽线虫细胞迁移方面发挥了重要作用。Src-L基因的突变导致远端尖细胞(DTC)以活性依赖和DTC细胞自主的方式指导性腺形态发生。在src-1突变体中，DTC不能转向并继续沿着腹肌进行离心式迁移。Src-L突变的作用被CED/Rac途径中功能基因的突变所抑制，这表明DTC中的Src-1是Rac途径的上游调节因子，控制细胞骨架重构。在src-1突变体中，UNC-5/netrin受体的表达受到正常调控，无论是UNC-5的早熟表达还是UNC-5基因的突变都不会显著影响DTC迁移缺陷。这些数据表明，SRC-1在DTCs的netrin信号转导中起作用。Src-1突变体在Q神经母细胞后代AVM和PVM的迁移和生长锥体路径寻找中也显示出细胞自主缺陷。然而，SRC-1的这些作用似乎并不涉及CED/RAC途径。这些发现表明，SRC-1通过不同细胞类型中不同的信号通路，对各种细胞外指导信号做出反应，指导细胞迁移。较少

The Src family of tyrosine kinases play pivotal roles in regulating cellular functions characteristic of multicellular animals, including cell-cell interactions, cell-substrate adhesion and cell migration. To investigate the functional alteration of Src kinases during evolution from a unicellular ancestor to multicellular animals, we characterized Src orthologs from the unicellular choanoflagellate Monosiga ovata and the primitive multicellular sponge Ephydatia fluviatilis. Here, we show that the src gene family and its C-terminal Src kinase (Csk)-mediated regulatory system were already established in the unicellular M.ovata and that this Src has unique features relative to multicellular Src : it can be phosphorylated by Csk at the negative regulatory site, but still exhibits substantial activity even in the phosphorylated form. Analyses of chimera molecules between M.ovata and E. fluviatilis Src orthologs reveal that structural alterations in the kinase domain are responsible for the … More inefficient negative regulation of M.ovata Src. When expressed in vertebrate fibroblasts, M.ovata Src can induce cell transformation irrespective of the presence of Csk. These findings suggest that a structure of Src required for the stable Csk-mediated negative regulation is still immature in the unicellular M.ovata, and that the development of stable negative regulation of Src may correlate with the evolution of multicellularity in animals.To address the fundamental roles Src in the multicellular animals, Effects of loss-of-function of Src in C.elegans was analyzed. Here we show that SRC-1, an orthologue of SFK, plays an essential role in directing cell migration in Caenorhabditis elegans. The mutation in the src-l gene results in defective distal tip cell (DTC)-directed gonad morphogenesis in an activity-dependent and DTC cell-autonomous manners. In the src-1 mutants, DTCs fail to turn and continue their centrifugal migration along the ventral muscles. The effect of the src-l mutation is suppressed by mutations in genes that function in the CED/Rac pathway, suggesting that SRC-1 in DTCs is an upstream regulator of a Rac pathway that controls cytoskeletal remodeling. In the src-1 mutant, the expression of unc-5/netrin receptor is normally regulated, and either the precocious expression of UNC-5 or the mutation in the unc-5 gene does not significantly affect the DTC migration defect. These data suggest that SRC-1 acts in the netrin signaling in DTCs. The src-1 mutant also exhibits cell-autonomous defects in the migration and growth cone path finding of Q neuroblast descendants AVM and PVM. However, these roles of SRC-1 do not appear to involve the CED/Rac pathway. These findings show that SRC-1 functions in responding to various extracellular guidance cues that direct the cell migration via disparate signaling pathways in different cell types. Less