Differentiated cytoplasmic granule formation in quiescent and non-quiescent cells upon chronological aging.

Hsin-Yi Lee,Jun-Yi Leu,Kuo-Yu Cheng,Jung-Chi Chao

doi:10.15698/mic2016.03.484

Hsin-Yi Lee, Jun-Yi Leu + Show 2 more

Open Access

https://doi.org/10.15698/mic2016.03.484

Copy DOI

Abstract

Stationary phase cultures represent a complicated cell population comprising at least two different cell types, quiescent (Q) and non-quiescent (NQ) cells. Q and NQ cells have different lifespans and cell physiologies. However, less is known about the organization of cytosolic protein structures in these two cell types. In this study, we examined Q and NQ cells for the formation of several stationary phase-prevalent granule structures including actin bodies, proteasome storage granules, stress granules, P-bodies, the compartment for unconventional protein secretion (CUPS), and Hsp42-associated stationary phase granules (Hsp42-SPGs). Most of these structures preferentially form in NQ cells, except for Hsp42-SPGs, which are enriched in Q cells. When nutrients are provided, NQ cells enter mitosis less efficiently than Q cells, likely due to the time requirement for reorganizing some granule structures. We observed that heat shock-induced misfolded proteins often colocalize to Hsp42-SPGs, and Q cells clear these protein aggregates more efficiently, suggesting that Hsp42-SPGs may play an important role in the stress resistance of Q cells. Finally, we show that the cell fate of NQ cells is largely irreversible even if they are allowed to reenter mitosis. Our results reveal that the formation of different granule structures may represent the early stage of cell type differentiation in yeast stationary phase cultures.

Highlights

Studies in the budding yeast Saccharomyces cerevisiae have contributed considerably to our knowledge of agingrelated genes and pathways [1]
We examined Q and NQ cells for the formation of several stationary phase-prevalent granule structures including actin bodies, proteasome storage granules, stress granules, P-bodies, the compartment for unconventional protein secretion (CUPS), and Hsp42associated stationary phase granules (Hsp42-SPGs)
Consistent with previous observations, NQ cells exhibited a lower rebudding frequency (61 ± 2.9% of NQ cells vs 98 ± 1.1% of Q cells in 5-day cultures, Figure 4B), indicating that some of them had lost the ability to reproduce. These results indicate that NQ cells lose the ability to reenter mitosis during the stationary phase, but they become less efficient at cell cycle reentry upon fresh nutrient supplementation

Summary

Introduction

Studies in the budding yeast Saccharomyces cerevisiae have contributed considerably to our knowledge of agingrelated genes and pathways [1]. Two distinct models of aging processes have been established: replicative aging and chronological aging. The model of replicative aging defines lifespan by the number of daughter cells that a mother cell can produce before senescence [2]. The chronological lifespan (CLS) is defined by the time that a yeast cell can survive in a non-dividing state in stationary phase cultures [3]. When glucose supplies become limiting, in order to use available nonfermentable carbon sources yeast cells enter diauxic shift that changes cell metabolism from fermentation to respiration. After all carbon sources are exhausted, cells will eventually enter the stationary phase [3]. The CLS is measured by monitoring the ability of stationary phase cells to reenter mitotic growth over time when fresh carbon sources are provided.

Methods

Results

Conclusion