Accession numbers from Phylogenetic evidence for the modular evolution of metazoan signalling pathways

Communication among cells was paramount to the evolutionary increase in cell type diversity and, ultimately, the origin of large body size. Across the diversity of Metazoa, there are only few conserved cell signalling pathways known to orchestrate the complex cell and tissue interactions regulating development; thus, modification to these few pathways has been responsible for generating diversity during the evolution of animals. Here, we summarize evidence for the origin and putative function of the intracellular, membrane-bound and secreted components of seven metazoan cell signalling pathways with a special focus on early branching metazoans (ctenophores, poriferans, placozoans and cnidarians) and basal unikonts (amoebozoans, fungi, filastereans and choanoflagellates). We highlight the modular incorporation of intra- and extracellular components in each signalling pathway and suggest that increases in the complexity of the extracellular matrix may have further promoted the modulation of cell signalling during metazoan evolution. Most importantly, this updated view of metazoan signalling pathways highlights the need for explicit study of canonical signalling pathway components in taxa that do not operate a complete signalling pathway. Studies like these are critical for developing a deeper understanding of the evolution of cell signalling.

细胞间通信对于细胞类型多样性的演化扩增，乃至大型生物体体型的起源，均至关重要。纵观后生动物（Metazoa）的演化多样性，目前已知仅有少数保守的细胞信号通路能够调控发育过程中复杂的细胞与组织相互作用；因此，对这少数通路的修饰改造，正是推动动物演化过程中物种多样性产生的核心机制。本研究综述了7条后生动物细胞信号通路的细胞内、膜结合及分泌型组分的起源证据与推定功能，重点聚焦于早期分支后生动物（栉水母类、多孔动物类、扁盘动物类与刺胞动物类）以及基底单鞭毛类群（变形虫类、真菌、丝足虫类与领鞭毛虫类）。我们着重阐明了每条信号通路中细胞内与细胞外组分的模块化整合模式，并提出细胞外基质复杂度的提升，可能进一步促进了后生动物演化过程中细胞信号通路的调控优化。尤为关键的是，这一更新后的后生动物信号通路认知视角，凸显了一项亟待开展的研究方向：需针对不具备完整信号通路的类群，开展经典信号通路组分的系统性研究。此类研究对于深入解析细胞信号的演化历程具有至关重要的意义。