Kin Koryu, Schaap Pauline
School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain.
Genes (Basel). 2021 Mar 27;12(4):487. doi: 10.3390/genes12040487.
Multicellularity evolved repeatedly in the history of life, but how it unfolded varies greatly between different lineages. Dictyostelid social amoebas offer a good system to study the evolution of multicellular complexity, with a well-resolved phylogeny and molecular genetic tools being available. We compare the life cycles of the Dictyostelids with closely related amoebozoans to show that complex life cycles were already present in the unicellular common ancestor of Dictyostelids. We propose frost resistance as an early driver of multicellular evolution in Dictyostelids and show that the cell signalling pathways for differentiating spore and stalk cells evolved from that for encystation. The stalk cell differentiation program was further modified, possibly through gene duplication, to evolve a new cell type, cup cells, in Group 4 Dictyostelids. Studies in various multicellular organisms, including Dictyostelids, volvocine algae, and metazoans, suggest as a common principle in the evolution of multicellular complexity that unicellular regulatory programs for adapting to environmental change serve as "proto-cell types" for subsequent evolution of multicellular organisms. Later, new cell types could further evolve by duplicating and diversifying the "proto-cell type" gene regulatory networks.
多细胞性在生命史上曾多次演化，但它在不同谱系中的演化过程差异很大。盘基网柄菌属社会性变形虫提供了一个研究多细胞复杂性演化的良好系统，其系统发育关系明确，且有分子遗传学工具可用。我们将盘基网柄菌属的生命周期与亲缘关系密切的变形虫进行比较，以表明复杂的生命周期在盘基网柄菌属的单细胞共同祖先中就已存在。我们提出抗冻性是盘基网柄菌属多细胞演化的早期驱动力，并表明分化为孢子和柄细胞的细胞信号通路是从包囊化的信号通路演化而来的。柄细胞分化程序可能通过基因复制进一步发生改变，从而在第4组盘基网柄菌属中演化出一种新的细胞类型——杯状细胞。对包括盘基网柄菌属、团藻目藻类和后生动物在内的各种多细胞生物的研究表明，作为多细胞复杂性演化的一个共同原则，适应环境变化的单细胞调控程序充当了多细胞生物后续演化的“原始细胞类型”。后来，新的细胞类型可以通过复制和多样化“原始细胞类型”的基因调控网络进一步演化。
