Amoeboid cells are fundamental to animal biology and broadly distributed across animal diversity, but their evolutionary origin is unclear. The closest living relatives of animals, the choanoflagellates, display a polarized cell architecture (with an apical flagellum encircled by microvilli) that closely resembles that of epithelial cells and suggests homology, but this architecture differs strikingly from the deformable phenotype of animal amoeboid cells. Here, we show that choanoflagellates subjected to confinement differentiate into an amoeboid form by retracting their flagella and activating myosin-based motility. This switch allows escape from confinement and is conserved across choanoflagellate diversity. The conservation of the amoeboid cell phenotype across animals and choanoflagellates, together with the conserved role of myosin, is consistent with the homology of amoeboid motility in both lineages. We hypothesize that the differentiation between animal epithelial and crawling cells might have evolved from a stress-induced phenotypic switch between flagellate and amoeboid forms in their single-celled ancestors.

中文翻译：

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动物近亲中的鞭毛虫到变形虫的转换

变形虫细胞是动物生物学的基础，广泛分布于动物多样性中，但它们的进化起源尚不清楚。动物的近亲，领鞭毛虫，显示出一种极化的细胞结构（顶端鞭毛被微绒毛包围），与上皮细胞的结构非常相似，表明同源性，但这种结构与动物变形虫细胞的可变形表型截然不同。在这里，我们表明受到限制的领鞭毛虫通过缩回鞭毛并激活基于肌球蛋白的运动分化成变形虫形式。这个开关允许从限制中逃脱并且在领鞭毛虫多样性中是保守的。动物和领鞭毛虫中变形虫细胞表型的保护，以及肌球蛋白的保守作用，与两个谱系中变形虫运动的同源性一致。我们假设动物上皮细胞和爬行细胞之间的分化可能是由于应激诱导的单细胞祖先鞭毛和变形虫形式之间的表型转换进化而来的。