Table of contents

Volume 3, Issue 3, pp. 95 - 131, March 2016

Issue cover
Cover: Meiotic chromosomes develop a characteristic superstructure called the synaptonemal complex (SC) where homologous chromosomes are tightly aligned to each other. Budding yeast meiotic chromosomes with fully-assembled SC are shown. Yellow, DNA; green, Ecm11 (a central region protein of the SC); red, Red1 (a lateral element protein of the SC). Image by Hideo Tsubouchi (University of Sussex, UK); modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license. Enlarge issue cover

Editorial

Gearing up for survival – HSP-containing granules accumulate in quiescent cells and promote survival

Ruofan Yu and Weiwei Dang

page 95-96 | 10.15698/mic2016.03.481 | Full text | PDF |

News and Thoughts

Yeast screening platform identifies FDA-approved drugs that reduce Aβ oligomerization

Triana Amen and Daniel Kaganovich

page 97-100 | 10.15698/mic2016.03.482 | Full text | PDF |

In a nutshell

Mitochondrial regulation of cell death: a phylogenetically conserved control

Lorenzo Galluzzi, Oliver Kepp and Guido Kroemer

page 101-108 | 10.15698/mic2016.03.483 | Full text | PDF | Abstract

Mitochondria are fundamental for eukaryotic cells as they participate in critical catabolic and anabolic pathways. Moreover, mitochondria play a key role in the signal transduction cascades that precipitate many (but not all) regulated variants of cellular demise. In this short review, we discuss the differential implication of mitochondria in the major forms of regulated cell death.

Research Articles

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

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

page 109-119 | 10.15698/mic2016.03.484 | Full text | PDF | 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.

Research Reports

Towards understanding the gliotoxin detoxification mechanism: in vivo thiomethylation protects yeast from gliotoxin cytotoxicity

Elizabeth B. Smith, Stephen K. Dolan, David A. Fitzpatrick, Sean Doyle and Gary W. Jones

page 120-125 | 10.15698/mic2016.03.485 | Full text | PDF | Abstract

Gliotoxin (GT) is a mycotoxin produced by some species of ascomycete fungi including the opportunistic human pathogen Aspergillus fumigatus. In order to produce GT the host organism needs to have evolved a self-protection mechanism. GT contains a redox-cycling disulfide bridge that is important in mediating toxicity. Recently is has been demonstrated that A. fumigatus possesses a novel thiomethyltransferase protein called GtmA that has the ability to thiomethylate GT in vivo, which aids the organism in regulating GT biosynthesis. It has been suggested that thiomethylation of GT and similar sulfur-containing toxins may play a role in providing self-protection in host organisms. In this work we have engineered Saccharomyces cerevisiae, a GT-naïve organism, to express A. fumigatus GtmA. We demonstrate that GtmA can readily thiomethylate GT in yeast, which results in protection of the organism from exogenous GT. Our work has implications for understanding the evolution of GT self-protection mechanisms in organisms that are GT producers and non-producers.

Microreviews

Shaping meiotic chromosomes with SUMO: a feedback loop controls the assembly of the synaptonemal complex in budding yeast

Hideo Tsubouchi, Bilge Argunhan and Tomomi Tsubouchi

page 126-128 | 10.15698/mic2016.03.486 | Full text | PDF | Abstract

The synaptonemal complex (SC) is a meiosis-specific chromosomal structure in which homologous chromosomes are intimately linked through arrays of specialized proteins called transverse filaments (TF). Widely conserved in eukaryote meiosis, the SC forms during prophase I and is essential for accurate segregation of homologous chromosomes at meiosis I. However, the basic mechanism overlooking formation and regulation of the SC has been poorly understood. By using the budding yeast Saccharomyces cerevisiae, we recently showed that SC formation is controlled through the attachment of multiple molecules of small ubiquitin-like modifier (SUMO) to a regulator of TF assembly. Intriguingly, this SUMOylation is activated by TF, implicating the involvement of a positive feedback loop in the control of SC assembly. We discuss the implication of this finding and possible involvement of a similar mechanism in regulating other processes.

Mek1/Mre4 is a master regulator of meiotic recombination in budding yeast

Nancy M. Hollingsworth

page 129-131 | 10.15698/mic2016.03.487 | Full text | PDF | Abstract

Sexually reproducing organisms create gametes with half the somatic cell chromosome number so that fusion of gametes at fertilization does not change the ploidy of the cell. This reduction in chromosome number occurs by the specialized cell division of meiosis in which two rounds of chromosome segregation follow a single round of chromosome duplication. Meiotic crossovers formed between the non-sister chromatids of homologous chromosomes, combined with sister chromatid cohesion, physically connect homologs, thereby allowing proper segregation at the first meiotic division. Meiotic recombination is initiated by programmed double strand breaks (DSBs) whose repair is highly regulated such that (1) there is a bias for recombination with homologs rather than sister chromatids, (2) crossovers are distributed throughout the genome by a process called interference, (3) crossover homeostasis regulates the balance between crossover and non-crossover repair to maintain a critical number of crossovers and (4) each pair of homologs receives at least one crossover. It was previously known that the imposition of interhomolog bias in budding yeast requires meiosis-specific modifications to the DNA damage response and the local activation of the meiosis-specific Mek1/Mre4 (hereafter Mek1) kinase at DSBs. However, because inactivation of Mek1 results in intersister, rather than interhomolog DSB repair, whether Mek1 had a role in interhomolog pathway choice was unknown. A recent study by Chen et al. (2015) reveals that Mek1 indirectly regulates the crossover/non-crossover decision between homologs as well as genetic interference. It does this by enabling phosphorylation of Zip1, the meiosis-specific transverse filament protein of the synaptonemal complex (SC), by the conserved cell cycle kinase, Cdc7-Dbf4 (DDK). These results suggest that Mek1 is a “master regulator” of meiotic recombination in budding yeast.