School of Chemistry, University of Edinburgh, King's Buildings, Edinburgh EH9 3FJ, United Kingdom.
Department of Biotechnology, Akita Prefectural University, 241-438 Kaidobata-Nishi Shimoshinjo-Nakano, Akita 010-0195, Japan.
J Struct Biol. 2020 Apr 1;210(1):107476. doi: 10.1016/j.jsb.2020.107476. Epub 2020 Feb 1.
Coccolithophores are single-celled marine algae that produce calcified scales called coccoliths. Each scale is composed of anvil-shaped single crystals of calcite that are mechanically interlocked, constituting a remarkable example of the multi-level construction of mineralized structures. Coccolith formation starts with the nucleation of rhombohedral crystals on an organic substrate called base plate. The crystals then grow preferentially along specific directions to generate the mature structure, which is then transported to the outside of the cells. Here, we extracted forming coccoliths from Pleurochrysis carterae cells and used cryo-electron tomography to characterize, in their native, hydrated state, the three-dimensional morphology and arrangement of the crystals. Comparing the crystal morphology across three different stages of coccolith formation, we show that competition for space between adjacent crystals contributes significantly to regulation of morphology by constraining growth in certain directions. We further demonstrate that crystals within a coccolith ring develop at different rates and that each crystalline unit rests directly in contact with the base plate and overgrow the rim of the organic substrate during development.
颗石藻是一种单细胞海洋藻类，它们会产生一种叫做颗石的钙化鳞片。每个鳞片都是由方解石的单晶体构成的，这些单晶体呈钉头状，相互机械锁合，构成了矿化结构多层次构造的一个显著例子。颗石的形成始于在一个叫做基板的有机基质上形成菱面体晶体的成核。然后，晶体沿着特定的方向优先生长，生成成熟的结构，然后将其输送到细胞外部。在这里，我们从帕拉藻细胞中提取了正在形成的颗石，并使用冷冻电子断层扫描技术，在其天然的、水合状态下，对晶体的三维形态和排列进行了表征。通过比较颗石形成的三个不同阶段的晶体形态，我们表明，相邻晶体之间的空间竞争对形态的调节有很大的贡献，它限制了晶体在某些方向上的生长。我们进一步证明，在一个颗石环内的晶体以不同的速度发育，并且每个晶体单元在发育过程中直接与基板接触，并在有机基质的边缘上生长。
