Accelerated invagination of vacuoles as a stress response in chronically heat-stressed yeasts

Ayane Ishii,Tomohiro Sasanami,Kohei Takeda,Hiroyuki Kato,Yoshinobu Ichikawa,Keiji Tanaka,Masahito Kawai,Yoko Kimura,Kotomi Asakawa,Haruka Noda

doi:10.1038/s41598-018-20781-8

Ayane Ishii, Tomohiro Sasanami + Show 8 more

Open Access

https://doi.org/10.1038/s41598-018-20781-8

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Abstract

When exposed to sublethal high temperatures, budding yeast cells can survive for a period of time; however, a sufficient amount of ubiquitin is necessary for this survival. To understand the nature of the stress, we examined the morphological changes in yeast cells, focusing on the vacuoles. Changes in vacuolar morphology were notable, and ruffled vacuolar membranes, accelerated invaginations of vacuolar membranes, and vesicle-like formations were observed. These changes occurred in the absence of Atg1, Atg9 or Ivy1 but appeared to require endosomal sorting proteins, such as Vps23, Vps24 or Pep12. Furthermore, the serial sections of the vacuoles analysed using an electron microscopic analysis revealed that spherical invaginated structures were linked together in a vacuole. Because degradation of cell surface proteins is induced from heat stress, fusion of endosomal and vacuolar membranes might occur frequently in heat-stressed cells, and yeast cells might be able to cope with a rapid increase in vacuolar surface area by such invaginations.

Highlights

In response to elevated temperatures, organisms initiate a sequence of events that function to cushion these stresses[1,2,3,4]
The degradation of several cell surface proteins, such as transporters, proton pumps or pheromone receptors, after various heat stresses, and the increase in chitin content, which is most likely activated by the cell wall stress pathway, have been reported[12,13,14,15]; the physiological changes or consequences that occur in the cell after chronic heat stress and that change the cell into a heat-tolerant state have not been fully investigated
To understand the nature of chronic sublethal heat stress on yeast, we examined the physiological changes in the cells after the stress, and focused on the specific changes in vacuolar morphology in this study

Summary

Introduction

In response to elevated temperatures, organisms initiate a sequence of events that function to cushion these stresses[1,2,3,4]. We decided to carefully examine the vacuolar structures in the cell after exposure to chronic heat stress because the protein transport toward the vacuoles involves the K63-linked ubiquitination, and the ruffling of vacuolar membranes by heat stress has been reported[20]. On examination of vacuolar structures in ubi4Δ cells, we observed that many vacuoles were swollen and remained single-lobed after exposure to heat stress (Fig. 2a, Supplementary Fig. 1a).

Results

Conclusion