Saccharomyces cerevisiae samples stained with FUN-1 dye can be stored at ?20�C for later observation

Lactoferrin perturbs lipid rafts and requires integrity of Pma1p-lipid rafts association to exert its antifungal activity against Saccharomyces cerevisiae

Lactoferrin (Lf) is a bioactive milk-derived protein with remarkable wide-spectrum antifungal activity. To deepen our understanding of the molecular mechanisms underlying Lf cytotoxicity, the role of plasma membrane ergosterol- and sphingolipid-rich lipid rafts and their association with the proton pump Pma1p was explored. Pma1p was previously identified as a Lf-binding protein. Results showed that bovine Lf (bLf) perturbs ergosterol-rich lipid rafts organization by inducing intracellular accumulation of ergosterol. Using yeast mutant strains lacking lipid rafts-associated proteins or enzymes involved in the synthesis of ergosterol and sphingolipids, we found that perturbations in the composition of these membrane domains increase resistance to bLf-induced yeast cell death. Also, when Pma1p-lipid rafts association is compromised in the Pma1-10 mutant and in the absence of the Pma1p-binding protein Ast1p, the bLf killing activity is impaired. Altogether, results showed that the perturbation of lipid rafts and the inhibition of both Pma1p and V-ATPase activities mediate the antifungal activity of bLf. Since it is suggested that the combination of conventional antifungals with lipid rafts-disrupting compounds is a powerful antifungal approach, our data will help to pave the way for the use of bLf alone or in combination for the treatment/eradication of clinically and agronomically relevant yeast pathogens/fungi.

RNA Aptamers Rescue Mitochondrial Dysfunction in a Yeast Model of Huntington's Disease

Huntington’s disease (HD) is associated with the misfolding and aggregation of mutant huntingtin harboring an elongated polyglutamine stretch at its N terminus. A distinguishing pathological hallmark of HD is mitochondrial dysfunction. Any strategy that can restore the integrity of the mitochondrial environment should have beneficial consequences for the disease. Specific RNA aptamers were selected that were able to inhibit aggregation of elongated polyglutamine stretch containing mutant huntingtin fragment (103Q-htt). They were successful in reducing the calcium overload, which leads to mitochondrial membrane depolarization in case of HD. In one case, the level of Ca²⁺ was restored to the level of cells not expressing 103Q-htt, suggesting complete recovery. The presence of aptamers was able to increase mitochondrial mass in cells expressing 103Q-htt, along with rescuing loss of mitochondrial genome. The oxidative damage to the proteome was prevented, which led to increased viability of cells, as monitored by flow cytometry. Thus, the presence of aptamers was able to inhibit aggregation of mutant huntingtin fragment and restore mitochondrial dysfunction in the HD cell model, confirming the advantage of the strategy in a disease-relevant parameter.

A fluorescence-based assay for in vitro screening of Saprolegnia inhibitors

The incidence of fish pathogenic oomycetes, Saprolegnia, has increased significantly in aquaculture since the ban of malachite green. For the efficient characterization of anti-Saprolegnia therapeutics, simple accurate methods are required. However, the current screening methods are limited by time, and none of them are confirming the viability of treated spores or hyphae. In this study, a modified fluorescence-based assay for the in vitro screening of Saprolegnia inhibitors has been developed. This method involves the use of FUN-1 viability dye combined with calcofluor white M2R, and is based on the formation of orange-red cylindrical intravacuolar structures (CIVS) in metabolically active spores, hyphae and biofilms. Heat-killed and bronopol-treated Saprolegnia spores, hyphae and biofilms exhibited diffuse bright green fluorescence which confirms complete loss of viability. For boric acid-treated spores, no germination was observed. However, tiny CIVS were observed in 50% of treated spores which indicated reduction in their viability. Our results proved that FUN-1 dye is an efficient tool to distinguish between live and dead Saprolegnia spores, hyphae and biofilms and to monitor the change in Saprolegnia viability during qualitative evaluation of potential anti-Saprolegnia compounds.

Viability of Saccharomyces cerevisiae incorporated within silica and polysaccharide hosts monitored via time-resolved fluorescence

The viability of Saccharomyces cerevisiae in biocompatible polymers under different growth conditions and studied using time-resolved fluorescence techniques is presented. Two fluorophores, the viscosity sensitive probe 4-(4-(dimethylamino)styryl)-N-methyl-pyridiniumiodine (DASPMI) and the yeast viability stain 2-chloro-4-(2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene)-1-phenylquinolinium iodide (FUN-1) are used to elucidate information on the incorporated yeast cell viability. Variations in cell viscosity, which are indicative of the cell state, were obtained using DASPMI. Prior to observing FUN-1 in yeast cells using fluorescence lifetime imaging, its photophysics in solution and heterogeneous media were investigated. Time-resolved emission spectra were measured and analysed to associate lifetimes to the spectral emission. Preliminary results show that monitoring the fluorescence lifetime of FUN-1 may give a useful insight into cellular metabolism. The results indicate that both fluorophores may be used to monitor the entrapped yeast cell viability, which is important for in vitro studies and applications, such as that in the biofuel industry, where Saccharomyces cerevisiae are required to remain active in high ethanol environments.

A multiplexed immunofluorescence method identifies Phakopsora pachyrhizi Urediniospores and determines their viability

Soybean rust, caused by Phakopsora pachyrhizi, occurs concomitantly wherever soybean is grown in the tropical and subtropical regions of the world. After reports of its first occurrence in Brazil in 2001 and the continental United States in 2004, research on the disease and its pathogen has greatly increased. One area of research has focused on capturing urediniospores, primarily by rain collection or wind traps, and detecting them either by microscopic observations or by immunological or molecular techniques. This system of detection has been touted for use as a potential warning system to recommend early applications of fungicides. One shortcoming of the method has been an inability to determine whether the spores are viable. Our study developed a method to detect viable P. pachyrhizi urediniospores using an immunofluorescence assay combined with propidium iodide (PI) staining. Antibodies reacted to P. pachyrhizi and other Phakopsora spp. but did not react with other common soybean pathogens or most other rust fungi tested, based on an indirect immunofluorescence assay using fluorescein isothiocyanate-labeled secondary antibodies. Two vital staining techniques were used to assess viability of P. pachyrhizi urediniospores: one combined carboxy fluorescein diacetate (CFDA) and PI, and the other utilized (2-chloro-4-[2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene]-1-phenylquinolinium iodide] (FUN 1). Using the CFDA-PI method, viable spores stained green with CFDA and nonviable spores counterstained red with PI. Using the FUN 1 method, cylindrical intravacuolar structures were induced to form within metabolically active urediniospores, causing them to fluoresce bright red to reddish-orange, whereas dead spores, with no metabolic activity, had an extremely diffused, faint fluorescence. An immunofluorescence technique in combination with PI counterstaining was developed to specifically detect viable P. pachyrhizi urediniospores. The method is rapid and reliable, with a potential for application in forecasting soybean rust based on the detection of viable urediniospores.

Assessment of FUN-1 vital dye staining: Yeast with a block in the vacuolar sorting pathway have impaired ability to form CIVS when stained with FUN-1 fluorescent dye

FUN-1 [2-chloro-4-(2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene)-1-phenylquinolinium iodide] is a fluorescent dye used in studies of yeast and other fungi to monitor cell viability in the research lab and to assay for active fungal infection in the clinical setting. When the plasma membrane is intact, fungal cells internalize FUN-1 and the dye is seen as diffuse green cytosolic fluorescence. FUN-1 is then transported to the vacuole in metabolically active wild type cells and subsequently is compacted into fluorescent red cylindrical intravacuolar structures (CIVS) by an unknown transport pathway. This dye is used to determine yeast viability, as only live cells form CIVS. However, in live Saccharomyces cerevisiae with impaired protein sorting to the yeast vacuole, we report decreased to no CIVS formation, depending on the cellular location of the block in the sorting pathway. Cells with a block in vesicle-mediated transport from the Golgi to prevacuolar compartment (PVC) or with a block in recycling from the PVC to the Golgi demonstrate a substantial impairment in CIVS formation. Instead, the FUN-1 dye is seen either in small punctate structures under fluorescence or as diffuse red cytosol under white light. Thus, researchers using FUN-1 should be cognizant of the limitations of this procedure in determining cell viability as there are viable yeast mutants with impaired CIVS formation.

Human initiator caspases trigger apoptotic and autophagic phenotypes in Saccharomyces cerevisiae

Caspases are a family of proteases that participate in the progression and execution of the apoptotic program. However, regulation of the caspase activation and their substrates has not yet been fully elucidated. Here we explore the effect of the ectopic expression of the human initiator caspases-8 and -10 in Saccharomyces cerevisiae. Our results showed that the expression of human CASP10 and CASP8 triggers certain apoptotic markers such as a massive production of reactive oxygen species (ROS), chromatin condensation and phosphatidylserine externalization, finally leading to cell death. In response to hydroxyurea (HU), yeast cells expressing caspase-10 did not reduce the replication of DNA and escaped to the intra-S checkpoint of the cell cycle. In addition, caspase-10 expression induced yeast vacuolization and a vacuole-associated phenotype resembling autophagy. Other intracellular alterations such as disorganization of the actin cytoskeleton, cell wall damage, and aberrations within the endoplasmic reticulum lumen were also associated with caspase-10 expression. Furthermore, caspase-induced cell death was completely dependent on the proteolytic activation of the enzyme but, in contrast, was not dependent on either of the endogenous yeast apoptotic proteins Aif1 and Mca1 or the mitochondria.