Screening for Toxic Amyloid in Yeast Exemplifies the Role of Alternative Pathway Responsible for Cytotoxicity

The relationship between amyloid and toxic species is a central problem since the discovery of amyloid structures in different diseases. Despite intensive efforts in the field, the deleterious species remains unknown at the molecular level. This may reflect the lack of any structure-toxicity study based on a genetic approach. Here we show that a structure-toxicity study without any biochemical prerequisite can be successfully achieved in yeast. A PCR mutagenesis of the amyloid domain of HET-s leads to the identification of a mutant that might impair cellular viability. Cellular and biochemical analyses demonstrate that this toxic mutant forms GFP-amyloid aggregates that differ from the wild-type aggregates in their shape, size and molecular organization. The chaperone Hsp104 that helps to disassemble protein aggregates is strictly required for the cellular toxicity. Our structure-toxicity study suggests that the smallest aggregates are the most toxic, and opens a new way to analyze the relationship between structure and toxicity of amyloid species

Guidelines and Recommendations on Yeast Cell Death Nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cellular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the definition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death routines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the authors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the progress of this vibrant field of research

Stream dissolved organic matter in permafrost regions shows surprising compositional similarities but negative priming and nutrient effects

Permafrost degradation is delivering bioavailable dissolved organic matter (DOM) and inorganic nutrients to surface water networks. While these permafrost subsidies represent a small portion of total fluvial DOM and nutrient fluxes, they could influence food webs and net ecosystem carbon balance via priming or nutrient effects that destabilize background DOM. We investigated how addition of biolabile carbon (acetate) and inorganic nutrients (nitrogen and phosphorus) affected DOM decomposition with 28-day incubations. We incubated late-summer stream water from 23 locations nested in seven northern or high-altitude regions in Asia, Europe, and North America. DOM loss ranged from 3% to 52%, showing a variety of longitudinal patterns within stream networks. DOM optical properties varied widely, but DOM showed compositional similarity based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Addition of acetate and nutrients decreased bulk DOM mineralization (i.e., negative priming), with more negative effects on biodegradable DOM but neutral or positive effects on stable DOM. Unexpectedly, acetate and nutrients triggered breakdown of colored DOM (CDOM), with median decreases of 1.6% in the control and 22% in the amended treatment. Additionally, the uptake of added acetate was strongly limited by nutrient availability across sites. These findings suggest that biolabile DOM and nutrients released from degrading permafrost may decrease background DOM mineralization but alter stoichiometry and light conditions in receiving waterbodies. We conclude that priming and nutrient effects are coupled in northern aquatic ecosystems and that quantifying two-way interactions between DOM properties and environmental conditions could resolve conflicting observations about the drivers of DOM in permafrost zone waterways

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cel-lular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the defi-nition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differ-ential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death rou-tines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the au-thors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the pro-gress of this vibrant field of research

Le déficit en alpha-1 antitrypsine : modèle d’altération de l’homéostasie protéique ou protéostasie

International audienc

The [URE3] prion is not conserved among Saccharomyces species.

The [URE3] prion of Saccharomyces cerevisiae is a self-propagating inactive form of the nitrogen catabolism regulator Ure2p. To determine whether the [URE3] prion is conserved in S. cerevisiae-related yeast species, we have developed genetic tools allowing the detection of [URE3] in Saccharomyces paradoxus and Saccharomyces uvarum. We found that [URE3] is conserved in S. uvarum. In contrast, [URE3] was not detected in S. paradoxus. The inability of S. paradoxus Ure2p to switch to a prion isoform results from the primary sequence of the protein and not from the lack of cellular cofactors as heterologous Ure2p can propagate [URE3] in this species. Our data therefore demonstrate that [URE3] is conserved only in a subset of Saccharomyces species. Implications of our finding on the physiological and evolutionary meaning of the yeast [URE3] prion are discussed

Functional analysis of Rrp7p, an essential yeast protein involved in pre-rRNA processing and ribosome assembly.

During the functional analysis of open reading frames (ORFs) identified during the sequencing of chromosome III of Saccharomyces cerevisiae, the previously uncharacterized ORF YCL031C (now designated RRP7) was deleted. RRP7 is essential for cell viability, and a conditional null allele was therefore constructed, by placing its expression under the control of a regulated GAL promoter. Genetic depletion of Rrp7p inhibited the pre-rRNA processing steps that lead to the production of the 20S pre-rRNA, resulting in reduced synthesis of the 18S rRNA and a reduced ratio of 40S to 60S ribosomal subunits. A screen for multicopy suppressors of the lethality of the GAL::rrp7 allele isolated the two genes encoding a previously unidentified ribosomal protein (r-protein) that is highly homologous to the rat r-protein S27. When present in multiple copies, either gene can suppress the lethality of an RRP7 deletion mutation and can partially restore the ribosomal subunit ratio in Rrp7p-depleted cells. Deletion of both r-protein genes is lethal; deletion of either single gene has an effect on pre-rRNA processing similar to that of Rrp7p depletion. We believe that Rrp7p is required for correct assembly of rpS27 into the preribosomal particle, with the inhibition of pre-rRNA processing appearing as a consequence of this defect