Eye-like ocelloids are built from different endosymbiotically acquired components
Eye-like ocelloids are built from different endosymbiotically acquired components
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DOI：
10.1038/nature14593
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发表时间：
2015-07-09
期刊：
影响因子：
64.8
通讯作者：
Leander, Brian S.
中科院分区：
文献类型：
--
作者：
Gavelis, Gregory S.;Hayakawa, Shiho;Leander, Brian S.
多细胞性通常被认为是形态复杂性的先决条件，正如在几组动物中发现的相机型眼睛所示。一个值得注意的例外存在于单细胞真核生物中，称为甲藻，其中一些具有眼睛状的“ocelloid”，由角膜，透镜，虹膜和视网膜的亚细胞类似物组成（1）。这些眼突细胞是未培养的，在环境样品中很少遇到，模糊了ocelloid的功能和进化起源。在这里，我们显示，使用电子显微镜，断层扫描，分离的细胞器基因组学，和单细胞基因组学的组合，ocelloids是建立从预先存在的细胞器，包括角膜样层的线粒体和视网膜体的细胞质。我们发现，视网膜体形成了多甲藻素型质体网络的中心核心，而在甲藻及其近亲中，多甲藻素型质体是通过与红色藻的古老内共生而起源的（2）。因此，ocelloid是一种嵌合体结构，包含具有不同内共生历史的细胞器。单细胞生物体的解剖学复杂性可能受到可用于分化的成分的限制，但ocelloid表明，预先存在的细胞器可以组装成如此复杂的结构，以至于最初被误认为是多细胞眼（3）。虽然线粒体和质体主要被认为是它们的代谢作用，但它们也可以是更大结构复杂性的构建块。
Multicellularity is often considered a prerequisite for morphological complexity, as seen in the camera-type eyes found in several groups of animals. A notable exception exists in single-celled eukaryotes called dinoflagellates, some of which have an eye-like 'ocelloid' consisting of subcellular analogues to a cornea, lens, iris, and retina(1). These planktonic cells are uncultivated and rarely encountered in environmental samples, obscuring the function and evolutionary origin of the ocelloid. Here we show, using a combination of electron microscopy, tomography, isolated-organelle genomics, and single-cell genomics, that ocelloids are built from pre-existing organelles, including a cornea-like layer made of mitochondria and a retinal body made of anastomosing plastids. We find that the retinal body forms the central core of a network of peridinin-type plastids, which in dinoflagellates and their relatives originated through an ancient endosymbiosis with a red alga(2). As such, the ocelloid is a chimaeric structure, incorporating organelles with different endosymbiotic histories. The anatomical complexity of single-celled organisms may be limited by the components available for differentiation, but the ocelloid shows that preexisting organelles can be assembled into a structure so complex that it was initially mistaken for a multicellular eye(3). Although mitochondria and plastids are acknowledged chiefly for their metabolic roles, they can also be building blocks for greater structural complexity.