Vol. 02, 2015

Intracellular phase for an extracellular bacterial pathogen: MgtC shows the way

Audrey Bernut^1,#, Claudine Belon¹, Chantal Soscia², Sophie Bleves², Anne-Béatrice Blanc-Potard¹

This article discusses the article "A macrophage subversion factor is shared by intracellular and extracellular pathogens" by Belon et al. (PLoS Pathogens 11(6): e1004969, 2015).

Subverting lysosomal function in Trypanosoma brucei

Sam Alsford

This article discusses Koh et al. (2015) "The lysosomotropic drug LeuLeu-OMe induces lysosome disruption and autophagy-independent cell death in Trypanosoma brucei (Microbial Cell 2(8): 288-298).

A single mutation in the 15S rRNA gene confers non sense suppressor activity and interacts with mRF1 the release factor in yeast mitochondria

Ali Gargouri, Catherine Macadré and Jaga Lazowska

This article presents the nucleotide sequence of the mim3-1 mitochondrial ribosomal suppressor, acting on ochre mitochondrial mutations and one frameshift mutation in Saccharomyces cerevisiae. A hypothetical mechanism of suppression by "ribosome shifting" is also discussed in view of the nature of mutations suppressed and not suppressed.

The role of transcriptional ‘futile cycles’ in autophagy and microbial pathogenesis

Guowu Hu¹, Travis McQuiston¹, Amélie Bernard², Yoon-Dong Park¹, Jin Qiu¹, Ali Vural³, Nannan Zhang¹, Scott R. Waterman¹, Nathan H. Blewett⁴, Timothy G. Myers⁵, John H. Kehrl³, Gulbu Uzel¹, Daniel J. Klionsky² and Peter R. Williamson¹

Eukaryotic cells utilize macroautophagy (hereafter autophagy) to recycle cellular materials during nutrient stress. Target of rapamycin (Tor) is a central regulator of this process, acting by post-translational mechanisms, phosphorylating preformed autophagy-related (Atg) proteins to repress autophagy during log-phase growth. A role for this regulatory process in fungal virulence was further demonstrated by showing that overexpression of the Dcp2-associated mRNA-binding protein Vad1 in the AIDS-associated pathogen Cryptococcus neoformans results in constitutive repression of autophagy even under starvation conditions as well as attenuated virulence in a mouse model. In summary, Tor-dependent post-transcriptional regulation of autophagy plays a key role in the facilitation of microbial pathogenesis.

The many facets of homologous recombination at telomeres

Clémence Claussin and Michael Chang

The ends of linear chromosomes are capped by nucleoprotein structures called telomeres. A dysfunctional telomere may resemble a DNA double-strand break (DSB), which is a severe form of DNA damage. The presence of one DSB is sufficient to drive cell cycle arrest and cell death. Therefore cells have evolved mechanisms to repair DSBs such as homologous recombination (HR). HR-mediated repair of telomeres can lead to genome instability, a hallmark of cancer cells, which is why such repair is normally inhibited. However, some HR-mediated processes are required for proper telomere function. The need for some recombination activities at telomeres but not others necessitates careful and complex regulation, defects in which can lead to catastrophic consequences. Furthermore, some cell types can maintain telomeres via telomerase-independent, recombination-mediated mechanisms. In humans, these mechanisms...

The lysosomotropic drug LeuLeu-OMe induces lysosome disruption and autophagy-independent cell death in Trypanosoma brucei

Hazel Xinyu Koh^1,2, Htay Mon Aye¹, Kevin S. W. Tan² and Cynthia Y. He¹

Trypanosoma brucei is a blood-borne, protozoan parasite that causes African sleeping sickness in humans and nagana in animals. The current chemotherapy relies on only a handful of drugs that display undesirable toxicity, poor efficacy and drug-resistance. In this study, we explored the use of lysosomotropic drugs to induce bloodstream form T. brucei cell death via lysosome destabilization. We measured drug concentrations that inhibit cell proliferation by 50% (IC50) for several compounds, chosen based on their lysosomotropic effects previously reported in Plasmodium falciparum. The lysosomal effects and cell death induced by L-leucyl-L-leucyl methyl ester (LeuLeu-OMe) were further analyzed by flow cytometry and immunofluorescence analyses of different lysosomal markers...

From the baker to the bedside: yeast models of Parkinson’s disease

Regina Menezes^1,2, Sandra Tenreiro^3,5, Diana Macedo², Cláudia N. Santos^1,2, Tiago Fleming Outeiro^4,5,6

The baker’s yeast Saccharomyces cerevisiae has been extensively explored for our understanding of fundamental cell biology processes highly conserved in the eukaryotic kingdom. This review provides a brief historical perspective on the emergence of yeast as an experimental model and on how the field evolved to exploit the potential of the model for tackling the intricacies of various human diseases. In particular, the authors focus on existing yeast models of the molecular underpinnings of Parkinson’s disease (PD), focusing primarily on the central role of protein quality control systems.

Why are essential genes essential? – The essentiality of Saccharomyces genes

Zhaojie Zhang and Qun Ren

Essential genes are defined as required for the survival of an organism or a cell. This article reviews and analyzes the levels of essentiality of the Saccharomyces cerevisiae genes and groups the genes into four categories: (1) Conditional essential: essential only under certain circumstances or growth conditions; (2) Essential: required for survival under optimal growth conditions; (3) Redundant essential: synthetic lethal due to redundant pathways or gene duplication; and (4) Absolute essential: the minimal genes required for maintaining a cellular life under a stress-free environment. The essential and non-essential functions of the essential genes are further analyzed.

In Entamoeba histolytica, a BspA family protein is required for chemotaxis toward tumour necrosis factor

Anne Silvestre^{1, 2, 3, 4}, Aurélie Plaze^{1, 2}, Patricia Berthon^{3, 4}, Roman Thibeaux^{1, 2}, Nancy Guillen^{1, 2} and Elisabeth Labruyère^{1, 2}

Background: Entamoeba histolytica cell migration is essential for the development of human amoebiasis (an infectious disease characterized by tissue invasion and destruction). The tissue inflammation associated with tumour necrosis factor (TNF) secretion by host cells is a well-documented feature of amoebiasis. Tumour necrosis factor is a chemoattractant for E. histolytica, and the parasite may have a TNF receptor at its cell surface. Methods: confocal microscopy, RNA Sequencing, bioinformatics, RNA antisense techniques and histological analysis of human colon explants were used to characterize the interplay between TNF and E. histolytica. Results: an antibody against human TNF receptor 1 (TNFR1) stained the E. histolytica trophozoite...

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Modeling human Coenzyme A synthase mutation in yeast reveals altered mitochondrial function, lipid content and iron metabolism

Camilla Ceccatelli Berti¹, Cristina Dallabona¹, Mirca Lazzaretti¹, Sabrina Dusi², Elena Tosi¹, Valeria Tiranti², Paola Goffrini¹

Mutations in nuclear genes associated with defective coenzyme A biosynthesis have been identified as responsible for some forms of neurodegeneration with brain iron accumulation (NBIA), namely PKAN and CoPAN. Yeast expressing a pathogenic mutation exhibited a temperature-sensitive growth defect in the absence of pantothenate and a reduced CoA content. Additional characterization revealed decreased oxygen consumption, reduced activities of mitochondrial respiratory complexes, higher iron content, increased sensitivity to oxidative stress and reduced amount of lipid droplets, thus partially recapitulating the phenotypes found in patients and establishing yeast as a potential model to clarify the pathogenesis underlying PKAN and CoPAN diseases.

Understanding structure, function, and mutations in the mitochondrial ATP synthase

Ting Xu¹, Vijayakanth Pagadala², David M. Mueller¹

This review summarizes the current understanding of the subunit composition of the ATP synthase and the role of the subunits followed by a discussion on known mutations and their effect on the activity of the ATP synthase. The concludes with a summary of mutations in genes encoding subunits of the ATP synthase that are known to be responsible for human disease, and a brief discussion on SNPs.

Modeling non-hereditary mechanisms of Alzheimer disease during apoptosis in yeast

Ralf J. Braun^1,#, Cornelia Sommer^2,3,#, Christine Leibiger^1,#, Romina J.G. Gentier^4,#, Verónica I. Dumit⁵, Katrin Paduch¹, Tobias Eisenberg², Lukas Habernig², Gert Trausinger⁶, Christoph Magnes⁶, Thomas Pieber^6,7, Frank Sinner^6,7, Jörn Dengjel⁵, Fred W. van Leeuwen⁴, Guido Kroemer^8-11, and Frank Madeo^2,3

Impaired protein degradation and mitochondrial dysfunction are believed to contribute to neurodegenerative disorders, including Alzheimer disease (AD). This microreview comments on the article "Accumulation of Basic Amino Acids at Mitochondria Dictates the Cytotoxicity of Aberrant Ubiquitin" by Braun et al. (2015), Cell Rep.

Translate to divide: сontrol of the cell cycle by protein synthesis

Michael Polymenis¹ and Rodolfo Aramayo²

Protein synthesis underpins much of cell growth and, consequently, cell multiplication. Understanding how proliferating cells commit and progress into the cell cycle requires knowing not only which proteins need to be synthesized, but also what determines their rate of synthesis during cell division. Experiments with proliferating populations of microbial strains, animal or plant cell lines, have rigorous expectations. Under the same culture conditions, cells ought to have the same properties and composition in every single experiment. The basic “metrics” of proliferating cells remain constant, even after many rounds of cell division. These metrics include cellular mass and volume, and macromolecular composition. The constancy of such parameters reflects the fundamental ability of cells to coordinate their growth with their division. Balancing cell growth with cell division determines the overall rates of cell proliferation...

New roles for autophagy and spermidine in T cells

D. J. Puleston and A. K. Simon

This microreview discusses the article "Autophagy is a critical regulator of memory CD8+ T cell formation" by Puleston et al. (2014), eLife.

Characterization of the Maf family of polymorphic toxins in pathogenic Neisseria species

Anne Jamet^1,2,3,4,5, Xavier Nassif^2,3,4,5

In addition to harmless commensal species, Neisseria genus encompasses two pathogenic species, N. meningitidis (the meningococcus) and N. gonorrhoeae (the gonococcus), which are responsible for meningitis and genital tract infections, respectively. This microreview comments on the article "A new family of secreted toxins in pathogenic Neisseria species" by Jamet et al. (2015), PLoS Pathog.

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Histone deacetylases: revealing the molecular base of dimorphism in pathogenic fungi

Alberto Elías-Villalobos^1,2, Dominique Helmlinger² and José I. Ibeas¹

Fungi, as every living organism, interact with the external world and have to adapt to its fluctuations. For pathogenic fungi, such interaction involves adapting to the hostile environment of their host. Survival depends on the capacity of fungi to detect and respond to external stimuli, which is achieved through a tight and efficient genetic control. Elías-Villalobos et al. propose that histone acetylation is critical to the proper timing and induction of transcription of the genes encoding factors that coordinate changes in morphology with pathogenesis.

Electron microscopy for ultrastructural analysis and protein localization in Saccharomyces cerevisiae

Andri Frankl, Muriel Mari and Fulvio Reggiori

The yeast Saccharomyces cerevisiae is a key model system for studying of a multitude of cellular processes because of its amenability to genetics, molecular biology and biochemical procedures. The goal of this review is to guide researchers that want to investigate a particular process at the ultrastructural level in yeast by aiding in the selection of the most appropriate approach to visualize a specific structure or subcellular compartment.

A bacterial volatile signal for biofilm formation

Yun Chen², Kevin Gozzi¹, and Yunrong Chai¹

Bacteria constantly monitor the environment they reside in and respond to potential changes in the environment through a variety of signal sensing and transduction mechanisms in a timely fashion. In their recent study (Chen, et al. mBio (2015), 6: e00392-15), the authors demonstrated that the soil bacterium Bacillus subtilis uses acetic acid as a volatile signal to coordinate the timing of biofilm formation within physically separated cells in the community. They also showed that the bacterium possesses an intertwined gene network to produce, secrete, sense, and respond to acetic acid, in stimulating biofilm formation.

The great escape: Pseudomonas breaks out of the lung

Angelica Zhang¹, Stephanie M. Rangel¹, and Alan R. Hauser^1,2

The Gram-negative bacterium Pseudomonas aeruginosa is a major cause of hospital-acquired infections and the focus of much attention due to its resistance to many conventional antibiotics. This article discusses the potential mechanisms by which these processes occur as well as the novel techniques used to study ExoS function in vivo.

Peering into the ‘black box’ of pathogen recognition by cellular autophagy systems

Shu-chin Lai^# and Rodney J Devenish

Autophagy is an intracellular process that plays an important role in protecting eukaryotic cells and maintaining intracellular homeostasis. This review summarises the available evidence regarding the specific recognition of invading pathogens by which they are targeted into host autophagy pathways.

Per aspera ad astra: When harmful chromosomal translocations become a plus value in genetic evolution. Lessons from Saccharomyces cerevisiae

Valentina Tosato and Carlo V. Bruschi

This review will focus on chromosomal translocations (either spontaneous or induced) in budding yeast. Indeed, very few organisms tolerate so well aneuploidy like Saccharomyces, allowing in depth studies on chromosomal numerical aberrations. The phenomenon of post-translocational adaptation (PTA) is discussed, providing some new unpublished data and proposing the hypothesis that translocations may drive evolution through adaptive genetic selection.

Intracellular phase for an extracellular bacterial pathogen: MgtC shows the way

Audrey Bernut^1,#, Claudine Belon¹, Chantal Soscia², Sophie Bleves², Anne-Béatrice Blanc-Potard¹

This article discusses the article "A macrophage subversion factor is shared by intracellular and extracellular pathogens" by Belon et al. (PLoS Pathogens 11(6): e1004969, 2015).

The role of transcriptional ‘futile cycles’ in autophagy and microbial pathogenesis

The many facets of homologous recombination at telomeres

Clémence Claussin and Michael Chang

Quorum protection, growth and survival

Ian G . Macreadie

For the growth of a cell culture, one inoculates not with one cell but with a quorum of cells. This most often a requirement, not just a convenience, and most of us take this for granted without question. Here this observation is re-examined to understand why a quorum may be required to grow cells. The importance of quorums may be widespread in the aspects of microbiology they affect. It is very likely that quorums are connected with and have a large impact on the determination of Minimal Inhibitory Concentrations. It is also possible that low cell density may adversely affect cell survival, however, this is an area where even less is known. The need for a quorum might affect other aspects of microbial cell culture, cell isolation and cell preservation. Effects also extend to mammalian cell culture. Here I seek to review studies that have been documented and speculate on how the information might be utilized in the future.

The emerging role of complex modifications of tRNA^Lys_UUU in signaling pathways

Patrick C. Thiaville^1,2,3,4 and Valérie de Crécy-Lagard^2,4

This comment discusses the article "Loss of wobble uridine modification in tRNA anticodons interferes with TOR pathway signaling" by Scheidt et al (Microbial Cell, 2014).

Targeting of chromatin readers: a novel strategy used by the Shigella flexneri virulence effector OspF to reprogram transcription

December 28, 2014

In this microreview, the authors discuss the article "Shigella flexneri targets the HP1γ subcode through the phosphothreoninelyase OspF" by Harouz et al. (2014), EMBO J, 22 : 2606-2622.