Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot, Israel.
Life Sciences Core Facilities, Weizmann Institute of Science, Rehovot, Israel.
Nat Commun. 2023 Jan 30;14(1):480. doi: 10.1038/s41467-023-36112-z.
Diatoms are unicellular algae characterized by silica cell walls. These silica elements are known to be formed intracellularly in membrane-bound silica deposition vesicles and exocytosed after completion. How diatoms maintain membrane homeostasis during the exocytosis of these large and rigid silica elements remains unknown. Here we study the membrane dynamics during cell wall formation and exocytosis in two model diatom species, using live-cell confocal microscopy, transmission electron microscopy and cryo-electron tomography. Our results show that during its formation, the mineral phase is in tight association with the silica deposition vesicle membranes, which form a precise mold of the delicate geometrical patterns. We find that during exocytosis, the distal silica deposition vesicle membrane and the plasma membrane gradually detach from the mineral and disintegrate in the extracellular space, without any noticeable endocytic retrieval or extracellular repurposing. We demonstrate that within the cell, the proximal silica deposition vesicle membrane becomes the new barrier between the cell and its environment, and assumes the role of a new plasma membrane. These results provide direct structural observations of diatom silica exocytosis, and point to an extraordinary mechanism in which membrane homeostasis is maintained by discarding, rather than recycling, significant membrane patches.
硅藻是一种单细胞藻类，其特征是具有硅细胞壁。这些硅元素被认为是在膜结合的硅沉积小泡内形成的，并在完成后外排。硅藻在这些大而刚性的硅元素外排过程中如何维持膜的动态平衡仍不清楚。在这里，我们使用活细胞共聚焦显微镜、透射电子显微镜和冷冻电子断层扫描技术，研究了两种模式硅藻物种在细胞壁形成和外排过程中的膜动力学。我们的结果表明，在形成过程中，矿物质与硅沉积小泡膜紧密结合，形成了精细几何图案的精确模具。我们发现，在细胞外排过程中，远端硅沉积小泡膜和质膜逐渐与矿物质分离并在细胞外空间解体，没有明显的内吞回收或细胞外再利用。我们证明，在细胞内，近端硅沉积小泡膜成为细胞与其环境之间的新屏障，并承担新质膜的作用。这些结果提供了硅藻硅外排的直接结构观察结果，并指出了一种非凡的机制，即通过丢弃而不是回收大量膜片来维持膜的动态平衡。
