Quick-Freeze, Deep-Etch Electron Microscopy Reveals the Characteristic Architecture of the Fission Yeast Spore

Abstract

The spore of the fission yeast Schizosaccharomyces pombe is a dormant cell that is resistant to a variety of environmental stresses. The S. pombe spore is coated by a proteinaceous surface layer, termed the Isp3 layer because it comprises mainly Isp3 protein. Although thin-section electron microscopy and scanning electron microscopy have revealed the fundamental structure of the spore, its architecture remains unclear. Here we visualized S. pombe spores by using a quick-freeze replica electron microscopy (QFDE-EM) at nanometer resolution, which revealed novel characteristic structures. QFDE-EM revealed that the Isp3 layer exists as an interwoven fibrillar layer. On the spore cell membrane, many deep invaginations, which are longer than those on the vegetative cell membrane, are aligned in parallel. We also observed that during spore germination, the cell surface changes from a smooth to a dendritic filamentous structure, the latter being characteristic of vegetative cells. These findings provide significant insight into not only the structural composition of the spore, but also the mechanism underlying the stress response of the cell.

Wake-up alarm: virtual time-lapse gene expression landscape illuminates mechanisms underlying dormancy breaking of germinating spores

“…Images for H3.c1-GFP (histone H3 copy 1 encoded by hht1) of the same cells (green) and schematics are also shown. Scale bar (bottom), 10 µm nutrition; they are round, and spore walls are harder than the cell walls of vegetative cells (Yoo et al 1973;Tahara et al 2020). This is partly due to sporulation-specific wall components, including β-glucan and chitin synthesised by Bgs2…”

“…Formation of the germ projection and its outgrowth are actin-dependent landmark events in the middle-to-late stages of the whole germination process in yeast (Hatanaka and Shimoda 2001;Kono et al 2005;Tahara et al 2020). The mechanism of symmetry breaking in the round shape of a spore has recently been revealed.…”

Involvement of a Multidrug Efflux Pump and Alterations in Cell Surface Structure in the Synergistic Antifungal Activity of Nagilactone E and Anethole against Budding Yeast Saccharomyces cerevisiae

“…However, no significant difference was observed in the electron micrographs. In contrast, similar fibrous structures of the outermost layer were observed in the vegetative cells of the fission yeast, Schizosaccharomyces pombe [33]. These fibers are known to consist of galactomannan in S. pombe [34].…”

“…The cells were washed twice with HEPES buffer and harvested by centrifugation. The cells were mixed with a slurry that included mica flakes, placed on a rabbit lung slab, and frozen using CryoPress (Valiant Instruments, St. Louis, MO, USA) that was cooled using liquid helium [33,40]. The slurry was used to retain the appropriate volume of water before freezing.…”

Special Issue: Formation and Function of Fungal Ascospores

“…The spore wall is the defining feature of the ascospore, and four studies added to our understanding of the organization of this remarkable extracellular matrix. Tahara et al have used a quick-freeze deep etch electron microscopy technique to reveal the architecture of the surface layers of the S. pombe spore wall [9]. The spore wall of S. cerevisiae contains an outer layer consisting of a polymer of the di-amino acid dityrosine.…”