Olson Bradley Jsc, Nedelcu Aurora M
Division of Biology, Kansas State University, Manhattan, KS, USA.
Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
Curr Opin Genet Dev. 2016 Aug;39:107-115. doi: 10.1016/j.gde.2016.06.003. Epub 2016 Jul 2.
Despite its major impact on the evolution of Life on Earth, the transition to multicellularity remains poorly understood, especially in terms of its genetic basis. The volvocine algae are a group of closely related species that range in morphology from unicellular individuals (Chlamydomonas) to undifferentiated multicellular forms (Gonium) and complex organisms with distinct developmental programs and one (Pleodorina) or two (Volvox) specialized cell types. Modern genetic approaches, complemented by the recent sequencing of genomes from several key species, revealed that co-option of existing genes and pathways is the primary driving force for the evolution of multicellularity in this lineage. The initial transition to undifferentiated multicellularity, as typified by the extant Gonium, was driven primarily by the co-option of cell cycle regulation. Further morphological and developmental innovations in the lineage leading to Volvox resulted from additional co-option events involving genes important for embryonic inversion, asymmetric cell division, somatic and germ cell differentiation and the structure and function of the extracellular matrix. Because of their relatively low but variable levels of morphological and developmental complexity, simple underlying genetics and recent evolutionary history, the volvocine algae are providing significant insight into our understanding of the genetics and evolution of major developmental and morphological traits.
尽管向多细胞性的转变对地球上生命的进化产生了重大影响，但其仍未得到充分理解，尤其是在遗传基础方面。团藻目藻类是一组亲缘关系密切的物种，其形态从单细胞个体（衣藻属）到未分化的多细胞形式（盘藻属），再到具有独特发育程序以及一种（多星藻属）或两种（团藻属）特化细胞类型的复杂生物体。现代遗传学方法，辅以最近对几个关键物种基因组的测序，揭示了现有基因和通路的选择是该谱系中多细胞性进化的主要驱动力。向未分化多细胞性的最初转变，以现存的盘藻属为代表，主要是由细胞周期调控的选择驱动的。导致团藻属的谱系中进一步的形态和发育创新，源于涉及对胚胎反转、不对称细胞分裂、体细胞和生殖细胞分化以及细胞外基质的结构和功能重要的基因的额外选择事件。由于它们相对较低但形态和发育复杂性可变、潜在遗传学简单以及进化历史较近，团藻目藻类为我们理解主要发育和形态特征的遗传学和进化提供了重要见解。
