Institut Curie, PSL Research University, CNRS - UMR 144, 75005 Paris, France
Open Biol. 2018 Aug;8(8). doi: 10.1098/rsob.180052.
Cell-autonomous polarity in Metazoans is evolutionarily conserved. I assume that permanent polarity in unicellular eukaryotes is required for cell motion and sensory reception, integration of these two activities being an evolutionarily constrained function. Metazoans are unique in making cohesive multicellular organisms through complete cell divisions. They evolved a primary cilium/centrosome (PC/C) organ, ensuring similar functions to the basal body/flagellum of unicellular eukaryotes, but in different cells, or in the same cell at different moments. The possibility that this innovation contributed to the evolution of individuality, in being instrumental in the early specification of the germ line during development, is further discussed. Then, using the example of highly regenerative organisms like planarians, which have lost PC/C organ in dividing cells, I discuss the possibility that part of the remodelling necessary to reach a new higher-level unit of selection in multi-cellular organisms has been triggered by conflicts among individual cell polarities to reach an organismic polarity. Finally, I briefly consider organisms with a sensorimotor organ like the brain that requires exceedingly elongated polarized cells for its activity. I conclude that beyond critical consequences for embryo development, the conservation of cell-autonomous polarity in Metazoans had far-reaching implications for the evolution of individuality.
多细胞生物的细胞自主极性是进化保守的。我假设单细胞真核生物的永久极性对于细胞运动和感觉接收是必需的，这两种活动的整合是一种进化受限的功能。多细胞生物通过完全细胞分裂来形成有凝聚力的多细胞生物，这在进化上是独一无二的。它们进化出了一个中心粒/中心体（PC/C）器官，确保了与单细胞真核生物的基体/鞭毛类似的功能，但在不同的细胞中，或者在同一细胞的不同时刻。进一步讨论了这种创新可能有助于个体性的进化，因为它有助于在发育过程中早期特化生殖系。然后，我以具有高度再生能力的生物，如涡虫为例，讨论了在多细胞生物中达到新的更高选择水平所必需的部分重塑是如何由个体细胞极性之间的冲突触发的，以达到生物体极性。最后，我简要考虑了具有类似于大脑的感觉运动器官的生物，其活动需要非常伸长的极化细胞。我得出结论，除了对胚胎发育有重要影响外，多细胞动物中细胞自主极性的保守性对个体性的进化也有着深远的影响。
