DiOC6 staining reveals organelle structure and dynamics in living yeast cells

Acyl-CoA binding protein is required for lipid droplet degradation in the diatom Phaeodactylum tricornutum

Diatoms (Bacillariophyceae) accumulate neutral storage lipids in lipid droplets during stress conditions, which can be rapidly degraded and recycled when optimal conditions resume. Since nutrient and light availability fluctuate in marine environments, storage lipid turnover is essential for diatom dominance of marine ecosystems. Diatoms have garnered attention for their potential to provide a sustainable source of omega-3 fatty acids. Several independent proteomic studies of lipid droplets isolated from the model oleaginous pennate diatom Phaeodactylum tricornutum have identified a previously uncharacterized protein with an acyl-CoA binding (ACB) domain, Phatrdraft_48778, here referred to as Phaeodactylum tricornutum acyl-CoA binding protein (PtACBP). We report the phenotypic effects of CRISPR-Cas9 targeted genome editing of PtACBP. ptacbp mutants were defective in lipid droplet and triacylglycerol degradation, as well as lipid and eicosapentaenoic acid synthesis, during recovery from nitrogen starvation. Transcription of genes responsible for peroxisomal β-oxidation, triacylglycerol lipolysis, and eicosapentaenoic acid synthesis was inhibited. A lipid-binding assay using a synthetic ACB domain from PtACBP indicated preferential binding specificity toward certain polar lipids. PtACBP fused to eGFP displayed an endomembrane-like pattern, which surrounded the periphery of lipid droplets. PtACBP is likely responsible for intracellular acyl transport, affecting cell division, development, photosynthesis, and stress response. A deeper understanding of the molecular mechanisms governing storage lipid turnover will be crucial for developing diatoms and other microalgae as biotechnological cell factories.

rtPA-loaded fucoidan polymer microbubbles for the targeted treatment of stroke

Systemic injection of thrombolytic drugs is the gold standard treatment for non-invasive blood clot resolution. The most serious risks associated with the intravenous injection of tissue plasminogen activator-like proteins are the bleeding complication and the dose related neurotoxicity. Indeed, the drug has to be injected in high concentrations due to its short half-life, the presence of its natural blood inhibitor (PAI-1) and the fast hepatic clearance (0.9 mg/kg in humans, 10 mg/kg in mouse models). Overall, there is a serious need for a dose-reduced targeted treatment to overcome these issues. We present in this article a new acoustic cavitation-based method for polymer MBs synthesis, three times faster than current hydrodynamic-cavitation method. The generated MBs are ultrasound responsive, stable and biocompatible. Their functionalization enabled the efficient and targeted treatment of stroke, without side effects. The stabilizing shell of the MBs is composed of Poly-Isobutyl Cyanoacrylate (PIBCA), copolymerized with fucoidan. Widely studied for its targeting properties, fucoidan exhibit a nanomolar affinity for activated endothelium and activated platelets (P-selectins). Secondly, the thrombolytic agent (rtPA) was loaded onto microbubbles (MBs) with a simple adsorption protocol. Hence, the present study validated the in vivo efficiency of rtPA-loaded Fuco MBs to be over 50 % more efficient than regular free rtPA injection for stroke resolution. In addition, the relative injected rtPA grafted onto targeting MBs was 1/10th of the standard effective dose (1 mg/kg in mouse). As a result, no hemorrhagic event, BBB leakage nor unexpected tissue distribution were observed.

A detection method for neuronal death indicates abnormalities in intracellular membranous components in neuronal cells that underwent delayed death

Acute neuronal degeneration is always preceded under the light and electron microscopes by a stage called microvacuolation, which is characterized by a finely vacuolar alteration in the cytoplasm of the neurons destined to death. In this study, we reported a method for detecting neuronal death using two membrane-bound dyes, rhodamine R6 and DiOC₆(3), which may be associated with the so-called microvacuolation. This new method produced a spatiotemporally similar staining pattern to Fluoro-Jade B in kainic acid-damaged brains in mice. Further experiments showed that increased staining of rhodamine R6 and DiOC₆(3) was observed only in degenerated neurons, but not in glia, erythrocytes, or meninges. Different from Fluoro-Jade-related dyes, rhodamine R6 and DiOC₆(3) staining is highly sensitive to solvent extraction and detergent exposure. Staining with Nile red for phospholipids and filipin III for non-esterified cholesterol supports that the increased staining of rhodamine R6 and DiOC₆(3) might be associated with increased levels of phospholipids and free cholesterol in the perinuclear cytoplasm of damaged neurons. In addition to kainic acid-injected neuronal death, rhodamine R6 and DiOC₆(3) were similarly useful for detecting neuronal death in ischemic models either in vivo or in vitro. As far as we know, the staining with rhodamine R6 or DiOC₆(3) is one of a few histochemical methods for detecting neuronal death whose target molecules have been well defined and therefore may be useful for explaining experimental results as well as exploring the mechanisms of neuronal death. (250 words).

Whole and Purified Aqueous Extracts of Nigella sativa L. Seeds Attenuate Apoptosis and the Overproduction of Reactive Oxygen Species Triggered by p53 Over-Expression in the Yeast Saccharomyces cerevisiae

Plants are an important source of pharmacologically active compounds. In the present work, we characterize the impact of black cumin (Nigella sativa L.) aqueous extracts on a yeast model of p53-dependent apoptosis. To this end, the Saccharomyces cerevisiae recombinant strain over-expressing p53 was used. The over-expression of p53 triggers the expression of apoptotic markers: the externalization of phosphatidylserine, mitochondrial defect associated with cytochrome-c release and the induction of DNA strand breaks. These different effects were attenuated by Nigella sativa L. aqueous extracts, whereas these extracts have no effect on the level of p53 expression. Thus, we focus on the anti-apoptotic molecules present in the aqueous extract of Nigella sativa L. These extracts were purified and characterized by complementary chromatographic methods. Specific fluorescent probes were used to determine the effect of the extracts on yeast apoptosis. Yeast cells over-expressing p53 decrease in relative size and have lower mitochondrial content. The decrease in cell size was proportional to the decrease in mitochondrial content and of mitochondrial membrane potential (ΔΨm). These effects were prevented by the purified aqueous fraction obtained by fractionation with different columns, named C4 fraction. Yeast cell death was also characterized by reactive oxygen species (ROS) overproduction. In the presence of the C4 fraction, ROS overproduction was strongly reduced. We also noted that the C4 fraction promotes the cell growth of control yeast cells, which do not express p53, supporting the fact that this purified extract acts on cellular mediators activating cell proliferation independently of p53. Altogether, our data obtained on yeast cells over-expressing p53 demonstrate that anti-apoptotic molecules targeting p53-induced apoptosis associated with mitochondrial dysfunction and ROS overproduction are present in the aqueous extracts of Nigella seeds and in the purified aqueous C4 fraction.

Herbivorous Juvenile Grass Carp (Ctenopharyngodon idella) Fed with Genetically Modified MON 810 and DAS-59122 Maize Varieties Containing Cry Toxins: Intestinal Histological, Developmental, and Immunological Investigations

Feeding experiments with juvenile grass carp (Ctenopharyngodon idella) fed with genetically modified maize MON 810 or DAS-59122 dried leaf biomass were carried out with 1-, 3- and 6-month exposures. Dosages of 3–7 μg/fish/day Cry1Ab or 18-55 μg/fish/day Cry34Ab1 toxin did not cause mortality. No difference occurred in body or abdominal sac weights. No differences appeared in levels of inorganic phosphate, calcium, fructosamine, bile acids, triglycerides, cholesterol, and alanine and aspartame aminotransferases. DAS-59122 did not alter blood parameters tested after 3 months of feeding. MON 810 slightly decreased serum albumin levels compared to the control, only in one group. Tapeworm (Bothriocephalus acheilognathi) infection changed the levels of inorganic phosphate and calcium. Cry34Ab1 toxin appeared in blood (12.6 ± 1.9 ng/mL), but not in the muscle. It was detected in B. acheilognathi. Cry1Ab was hardly detectable in certain samples near the limit of detection. Degradation of Cry toxins was extremely quick in the fish gastrointestinal tract. After 6 months of feeding, only mild indications in certain serum parameters were observed: MON 810 slightly increased the level of apoptotic cells in the blood and reduced the number of thrombocytes in one group; DAS-59122 mildly increased the number of granulocytes compared to the near-isogenic line.

Human OVCA2 and its homolog FSH3-induced apoptosis in Saccharomyces cerevisiae

Mammalian ovarian tumor suppressor candidate 2 (OVCA2) gene belongs to the family of serine hydrolase (FSH). This study aimed to elucidate the functional similarities of OVCA2 with its yeast homolog genes (FSH1, FSH2, and FSH3) regarding apoptosis. We found that the expression of OVCA2 in Saccharomyces cerevisiae increased production of reactive oxygen species (ROS), decreased cell growth, disturbed mitochondrial morphology, reduced membrane potential, increased chromatin condensation, and externalization of phosphatidylserine (PS) (annexin V/propidium iodide staining) indicating induced apoptotic cell death in yeast. We also showed that complementation of OVCA2 in fsh3Δ cells reduced cell growth and increased the apoptotic phenotypes. Collectively, our results suggest that complementation of human OVCA2 in fsh3Δ cells induced apoptosis in S. cerevisiae.

Miro (Mitochondrial Rho GTPase), a key player of mitochondrial axonal transport and mitochondrial dynamics in neurodegenerative diseases

Miro (mitochondrial Rho GTPases) a mitochondrial outer membrane protein, plays a vital role in the microtubule-based mitochondrial axonal transport, mitochondrial dynamics (fusion and fission) and Mito-Ca²⁺ homeostasis. It forms a major protein complex with Milton (an adaptor protein), kinesin and dynein (motor proteins), and facilitates bidirectional mitochondrial axonal transport such as anterograde and retrograde transport. By forming this protein complex, Miro facilitates the mitochondrial axonal transport and fulfills the neuronal energy demand, maintain the mitochondrial homeostasis and neuronal survival. It has been demonstrated that altered mitochondrial biogenesis, improper mitochondrial axonal transport, and mitochondrial dynamics are the early pathologies associated with most of the neurodegenerative diseases (NDs). Being the sole mitochondrial outer membrane protein associated with mitochondrial axonal transport-related processes, Miro proteins can be one of the key players in various NDs such as Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD). Thus, in the current review, we have discussed the evolutionarily conserved Miro proteins and its role in the pathogenesis of the various NDs. From this, we indicated that Miro proteins may act as a potential target for a novel therapeutic intervention for the treatment of various NDs.

Extracellular loops matter - subcellular location and function of the lysine transporter Lyp1 from Saccharomyces cerevisiae

Yeast amino acid transporters of the APC superfamily are responsible for the proton motive force-driven uptake of amino acids into the cell, which for most secondary transporters is a reversible process. The l-lysine proton symporter Lyp1 of Saccharomyces cerevisiae is special in that the Michaelis constant from out-to-in transport ( K m out → in ) is much lower than K m in → out , which allows accumulation of l-lysine to submolar concentration. It has been proposed that high intracellular lysine is part of the antioxidant mechanism of the cell. The molecular basis for the unique kinetic properties of Lyp1 is unknown. We compared the sequence of Lyp1 with APC para- and orthologues and find structural features that set Lyp1 apart, including differences in extracellular loop regions. We screened the extracellular loops by alanine mutagenesis and determined Lyp1 localization and activity and find positions that affect either the localization or activity of Lyp1. Half of the affected mutants are located in the extension of extracellular loop 3 or in a predicted α-helix in extracellular loop 4. Our data indicate that extracellular loops not only connect the transmembrane helices but also serve functionally important roles.

Deletion of Voltage-Dependent Anion Channel 1 knocks mitochondria down triggering metabolic rewiring in yeast

The Voltage-Dependent Anion-selective Channel (VDAC) is the pore-forming protein of mitochondrial outer membrane, allowing metabolites and ions exchanges. In Saccharomyces cerevisiae, inactivation of POR1, encoding VDAC1, produces defective growth in the presence of non-fermentable carbon source. Here, we characterized the whole-genome expression pattern of a VDAC1-null strain (Δpor1) by microarray analysis, discovering that the expression of mitochondrial genes was completely abolished, as consequence of the dramatic reduction of mtDNA. To overcome organelle dysfunction, Δpor1 cells do not activate the rescue signaling retrograde response, as ρ0 cells, and rather carry out complete metabolic rewiring. The TCA cycle works in a "branched" fashion, shunting intermediates towards mitochondrial pyruvate generation via malic enzyme, and the glycolysis-derived pyruvate is pushed towards cytosolic utilization by PDH bypass rather than the canonical mitochondrial uptake. Overall, Δpor1 cells enhance phospholipid biosynthesis, accumulate lipid droplets, increase vacuoles and cell size, overproduce and excrete inositol. Such unexpected re-arrangement of whole metabolism suggests a regulatory role of VDAC1 in cell bioenergetics.

Mitofusin 2 in Mature Adipocytes Controls Adiposity and Body Weight

We found that exposure of adult animals to caloriedense foods rapidly abolished expression of mitofusin 2 (Mfn2), a gene promoting mitochondrial fusion and mitochondrion-endoplasmic reticulum interactions, in white and brown fat. Mfn2 mRN was also robustly lower in obese human subjects compared with lean controls. Adipocyte-specific knockdown of Mfn2 in adult mice led to increased food intake, adiposity, and impaired glucose metabolism on standard chow as well as on a diet with high calorie content. The body weight and adiposity of mature adipocyte-specific Mfn2 knockout mice on a standard diet were similar to those of control mice on a high-fat diet. The transcriptional profile of the adipose tissue in adipocyte-specific Mfn2 knockout mice was consistent with adipocyte proliferation, increased lipogenesis at the tissue level, and decreased glucose utilization at the systemic level. These observations suggest a possible crucial role for mitochondrial dynamics in adipocytes in initiating systemic metabolic dysregulation.

Mancini et al. find that the mitochondrial fusion protein Mfn2 is lower in adipose tissue of mice on a high-fat diet and that of obese humans and that this protein in the fat is important for systemic control of metabolism.

Assays for Monitoring the Effects of Nicotinamide Supplementation on Mitochondrial Activity in Saccharomyces cerevisiae

The single-celled yeast Saccharomyces cerevisiae is one of the most valuable laboratory models that has been used successfully to identify factors and pathways involved in several cellular processes, the counterparts of which are evolutionarily conserved. Furthermore, it is also a powerful tool for analyzing the effects of molecules of nutraceutical interest with the view of leading to human health benefits and improving the quality of aging. In this context, we present some of the methods that have allowed us to assess the beneficial influence of a form of vitamin B3, namely nicotinamide, on mitochondrial functionality during yeast chronological aging. Mitochondrial dysfunctions are considered to be hallmarks of aging, and of several metabolic and neurodegenerative diseases. More specifically, these methods concern the determination of the respiratory parameters in intact cells in order to evaluate the efficiency of mitochondrial respiration in concert with the risk of superoxide anion (O₂^-) production, which results from inefficient respiration. In addition, we describe fluorescent staining specific for O₂^- detection and mitochondrial membrane potential, as well as a simple clonogenic assay based on the ability of cells to grow on a carbon source that requires a functional mitochondrial metabolism.

Crosstalk between protein N-glycosylation and lipid metabolism in Saccharomyces cerevisiae

The endoplasmic reticulum (ER) is a multi functional organelle and plays a crucial role in protein folding and lipid biosynthesis. The SEC59 gene encodes dolichol kinase, required for protein glycosylation in the ER. The mutation of sec59-1 caused a protein N-glycosylation defect mediated ER stress resulting in increased levels of phospholipid, neutral lipid and sterol, whereas growth was reduced. In the sec59-1∆ cell, the N-glycosylation of vacuolar carboxy peptidase-Y (CPY) was significantly reduced; whereas the ER stress marker Kar2p and unfolded protein response (UPR) were significantly increased. Increased levels of Triacylglycerol (TAG), sterol ester (SE), and lipid droplets (LD) could be attributed to up-regulation of DPP1, LRO1, and ARE2 in the sec 59-1∆ cell. Also, the diacylglycerol (DAG), sterol (STE), and free fatty acids (FFA) levels were significantly increased, whereas the genes involved in peroxisome biogenesis and Pex3-EGFP levels were reduced when compared to the wild-type. The microarray data also revealed increased expression of genes involved in phospholipid, TAG, fatty acid, sterol synthesis, and phospholipid transport resulting in dysregulation of lipid homeostasis in the sec59-1∆ cell. We conclude that SEC59 dependent N-glycosylation is required for lipid homeostasis, peroxisome biogenesis, and ER protein quality control.

Different rates of endocytic activity and vesicle transport from the apical and synaptic poles of the outer hair cell

Background

Intense endocytic activity at the apex of outer hair cells (OHCs)—the electromechanical cells of the cochlea—has been demonstrated using the vital plasma-membrane marker FM1-43 and confocal laser-scanning microscopy. Vesicular traffic toward the cell nucleus to distinct locations of the endoplasmic reticulum has also been shown.

Objective

The current study characterizes the dynamics of endocytic activity, as well as apicobasal and basoapical trafficking, using a local perfusion technique that we recently developed and published to visualize bidirectional trafficking in isolated bipolar cells.

Materials and methods

The fluorescent plasma-membrane markers FM1-43 (10 µM) and FM4-64 (10 µM), together with a fluid-phase marker, Lucifer yellow (50 µM), were used to label endocytosed vesicles in isolated OHCs of the guinea pig cochlea. Targets of endocytosed vesicles were examined with a fluorescent marker of subsurface cisternae, DiOC₆ (0.87 µM). Single- and two-photon confocal laser-scanning microscopy was used to visualize labeled vesicles.

Results

The plasma-membrane markers presented more intense vesicle internalization at the synaptic pole than at the apical pole of the OHC. Intracellular basoapical vesicle trafficking was faster than apicobasal trafficking. Vesicles endocytosed at the synaptic pole were transcytosed to the endoplasmic reticulum system. An intracellular Lucifer yellow signal was not detected.

Conclusion

The larger endocytic fluorescent signals in the synaptic pole and the faster basoapical trafficking imply that membrane internalization and vesicle trafficking are more efficient at the synaptic pole than at the apical pole of the OHC.

Relationship between mitofusin 2 and cancer

Mitochondria are dynamic organelles whose actions are fundamental for cell viability. Within the cell, the mitochondrial system is incessantly modified via the balance between fusion and fission processes. Among other proteins, mitofusin 2 is a central protagonist in all these mitochondrial events (fusion, trafficking, contacts with other organelles), the balance of which causes the correct mitochondrial action, shape, and distribution within the cell. Here we examine the structural and functional characteristics of mitofusin 2, underlining its essential role in numerous intracellular pathways, as well as in the pathogenesis of cancer.

Fluorescent Tracking of the Endoplasmic Reticulum in Live Pathogenic Fungal Cells

In fungal cells, the endoplasmic reticulum (ER) harbors several of the enzymes involved in the biosynthesis of ergosterol, an essential membrane component, making this organelle the site of action of antifungal azole drugs, used as a first-line treatment for fungal infections. This highlights the need for specific fluorescent labeling of this organelle in cells of pathogenic fungi. Here we report on the development and evaluation of a collection of fluorescent ER trackers in a panel of Candida, considered the most frequently encountered pathogen in fungal infections. These trackers enabled imaging of the ER in live fungal cells. Organelle specificity was associated with the expression of the target enzyme of antifungal azoles that resides in the ER; specific ER labeling was not observed in mutant cells lacking this enzyme. Labeling of live Candida cells with a combination of a mitotracker and one of the novel fungal ER trackers revealed sites of contact between the ER and mitochondria. These fungal ER trackers therefore offer unique molecular tools for the study of the ER and its interactions with other organelles in live cells of pathogenic fungi.

Spleen tyrosine kinase-dependent Nrf2 activation regulates oxidative stress-induced cell death in WiL2-NS human B lymphoblasts

Autoimmune rheumatic lesions are often characterised by the immune cell recruitment including B lymphocytes and the presence of reactive oxygen species (ROS), which increase antioxidant gene transcription via nuclear factor (erythroid-derived 2)-like 2 (Nrf2). Spleen tyrosine kinase (Syk) has a major role in the signal transmission of all haematopoietic lineage cells including B/T cells, mast cells, and macrophages. In this study, we investigated whether B cell survival is regulated by Nrf2 via ROS-mediated Syk activation in WiL2-NS human B lymphoblast cells. When WiL2-NS cells were incubated with 1% foetal bovine serum (FBS), the survival rate and mitochondrial membrane potential (MMP) were reduced. In addition, 1% FBS increased caspase 3 activity, cytochrome C release, nuclear localisation of Nrf2, and ROS production. N-acetylcysteine attenuated ROS production and nuclear translocation of Nrf2. It also inhibited cell death, caspase 3 activation, MMP collapse, and cytochrome C release. Results from the 1% FBS treatment were consistent with those of H₂O₂ treatment. Syk phosphorylation at tyrosine 525/526 was increased by incubation with 1% FBS or treatment with 100 µM H₂O₂. Nuclear translocation of Nrf2 by H₂O₂ was inhibited by treatment with BAY61-3606, a Syk inhibitor. BAY61-3606 also promoted MMP collapse, cytochrome C release, caspase 3 activation, and cell death. Taken together, these results implicate that Syk controls oxidative stress-induced human B cell death via nuclear translocation of Nrf2 and MMP collapse. These results suggest that Syk is a novel regulator of Nrf2 activation.

Localizing Antifungal Drugs to the Correct Organelle Can Markedly Enhance their Efficacy

A critical aspect of drug design is optimal target inhibition by specifically delivering the drug molecule not only to the target tissue or cell but also to its therapeutically active site within the cell. This study demonstrates, as a proof of principle, that drug efficacy can be increased considerably by a structural modification that targets it to the relevant organelle. Specifically, by varying the fluorescent dye segment an antifungal azole was directed from the fungal cell mitochondria to the endoplasmic reticulum (ER), the organelle that harbors the drug target. The ER-localized azole displayed up to two orders of magnitude improved antifungal activity and also dramatically reduced the growth of drug-tolerant fungal subpopulations in a panel of Candida species, which are the most prevalent causes of serious human fungal infections. The principle underlying the "target organelle localization" approach provides a new paradigm to improve drug potency and replenish the limited pipeline of antifungal drugs.

Effect of U(VI) aqueous speciation on the binding of uranium by the cell surface of Rhodotorula mucilaginosa, a natural yeast isolate from bentonites

This study presents the effect of aqueous uranium speciation (U-hydroxides and U-hydroxo-carbonates) on the interaction of this radionuclide with the cells of the yeast Rhodotorula mucigilanosa BII-R8. This strain was isolated from Spanish bentonites considered as reference materials for the engineered barrier components of the future deep geological repository of radioactive waste. X-ray absorption and infrared spectroscopy showed that the aqueous uranium speciation has no effect on the uranium binding process by this yeast strain. The cells bind mobile uranium species (U-hydroxides and U-hydroxo-carbonates) from solution via a time-dependent process initiated by the adsorption of uranium species to carboxyl groups. This leads to the subsequent involvement of organic phosphate groups forming uranium complexes with a local coordination similar to that of the uranyl mineral phase meta-autunite. Scanning transmission electron microscopy with high angle annular dark field analysis showed uranium accumulations at the cell surface associated with phosphorus containing ligands. Moreover, the effect of uranium mobile species on the cell viability and metabolic activity was examined by means of flow cytometry techniques, revealing that the cell metabolism is more affected by higher concentrations of uranium than the cell viability. The results obtained in this work provide new insights on the interaction of uranium with bentonite natural yeast from genus Rhodotorula under deep geological repository relevant conditions.

Cyclic AMP Pathway Activation and Extracellular Zinc Induce Rapid Intracellular Zinc Mobilization in Candida albicans

Zinc is an essential micronutrient, required for a range of zinc-dependent enzymes and transcription factors. In mammalian cells, zinc serves as a second messenger molecule. However, a role for zinc in signaling has not yet been established in the fungal kingdom. Here, we used the intracellular zinc reporter, zinbo-5, which allowed visualization of zinc in the endoplasmic reticulum and other components of the internal membrane system in Candida albicans. We provide evidence for a link between cyclic AMP/PKA- and zinc-signaling in this major human fungal pathogen. Glucose stimulation, which triggers a cyclic AMP spike in this fungus resulted in rapid intracellular zinc mobilization and this “zinc flux” could be stimulated with phosphodiesterase inhibitors and blocked via inhibition of adenylate cyclase or PKA. A similar mobilization of intracellular zinc was generated by stimulation of cells with extracellular zinc and this effect could be reversed with the chelator EDTA. However, zinc-induced zinc flux was found to be cyclic AMP independent. In summary, we show that activation of the cyclic AMP/PKA pathway triggers intracellular zinc mobilization in a fungus. To our knowledge, this is the first described link between cyclic AMP signaling and zinc homeostasis in a human fungal pathogen.

Low mitochondrial activity within developing earthworm male germ-line cysts revealed by JC-1

The male germ-line cysts that occur in annelids appear to be a very convenient model for spermatogenesis studies. Germ-line cysts in the studied earthworm are composed of two compartments: (1) germ cells, where each cell is connected via one intercellular bridge to (2) an anuclear central cytoplasmic mass, the cytophore. In the present paper, confocal and transmission electron microscopy were used to follow the changes in the mitochondrial activity and ultrastructure within the cysts during spermatogenesis. JC-1 was used to visualize the populations of mitochondria with a high and low membrane potential. We used the spot detection Imaris software module to obtain the quantitative data. We counted and compared the 'mitochondrial spots' - the smallest detectable signals from mitochondria. It was found that in all of the stages of cyst development, the majority of mitochondria spots showed a green fluorescence, thus indicating a low mitochondrial membrane potential (MMP). Moreover, the number of active mitochondria spots that were visualized by red JC-1 fluorescence (high MMP) drastically decreased as spermatogenesis progressed. As much as 26% of the total number of mitochondrial spots in the spermatogonial cysts showed a high MMP - 19% in the spermatocytes, 24% in the isodiametric spermatids and 3% and 6%, respectively, in the cysts that were holding early and late elongate spermatids. The mitochondria were usually thread-like and had an electron-dense matrix and lamellar cristae. Then, during spermiogenesis, the mitochondria within both the spermatids and the cytophore had a tendency to form aggregates in which the mitochondria were cemented by an electron-dense material.

Probing the contractile vacuole as Achilles' heel of the biotrophic grapevine pathogen Plasmopara viticola

The causative agent of Grapevine Downy Mildew, the oomycete Plasmopara viticola, poses a serious threat to viticulture. In the current work, the contractile vacuole of the zoospore is analysed as potential target for novel plant protection strategies. Using a combination of electron microscopy, spinning disc confocal microscopy, and video differential interference contrast microscopy, we have followed the genesis and dynamics of this vacuole required during the search for the stomata, when the non-walled zoospore is exposed to hypotonic conditions. This subcellular description was combined with a pharmacological study, where the functionality of the contractile vacuole was blocked by manipulation of actin, by Na, Cu, and Al ions or by inhibition of the NADPH oxidase. We further observe that RGD peptides (mimicking binding sites for integrins at the extracellular matrix) can inhibit the function of the contractile vacuole as well. Finally, we show that an extract from Chinese liquorice (Glycyrrhiza uralensis) proposed as biocontrol for Downy Mildews can efficiently induce zoospore burst and that this activity depends on the activity of NADPH oxidase. The effect of the extract can be phenocopied by its major compound, glycyrrhizin, suggesting a mode of action for this biologically safe alternative to copper products.

A systematic genomic screen implicates nucleocytoplasmic transport and membrane growth in nuclear size control

How cells control the overall size and growth of membrane-bound organelles is an important unanswered question of cell biology. Fission yeast cells maintain a nuclear size proportional to cellular size, resulting in a constant ratio between nuclear and cellular volumes (N/C ratio). We have conducted a genome-wide visual screen of a fission yeast gene deletion collection for viable mutants altered in their N/C ratio, and have found that defects in both nucleocytoplasmic mRNA transport and lipid synthesis alter the N/C ratio. Perturbing nuclear mRNA export results in accumulation of both mRNA and protein within the nucleus, and leads to an increase in the N/C ratio which is dependent on new membrane synthesis. Disruption of lipid synthesis dysregulates nuclear membrane growth and results in an enlarged N/C ratio. We propose that both properly regulated nucleocytoplasmic transport and nuclear membrane growth are central to the control of nuclear growth and size.

High resolution microscopy reveals the nuclear shape of budding yeast during cell cycle and in various biological states

How spatial organization of the genome depends on nuclear shape is unknown, mostly because accurate nuclear size and shape measurement is technically challenging. In large cell populations of the yeast Saccharomyces cerevisiae, we assessed the geometry (size and shape) of nuclei in three dimensions with a resolution of 30 nm. We improved an automated fluorescence localization method by implementing a post-acquisition correction of the spherical microscopic aberration along the z-axis, to detect the three dimensional (3D) positions of nuclear pore complexes (NPCs) in the nuclear envelope. Here, we used a method called NucQuant to accurately estimate the geometry of nuclei in 3D throughout the cell cycle. To increase the robustness of the statistics, we aggregated thousands of detected NPCs from a cell population in a single representation using the nucleolus or the spindle pole body (SPB) as references to align nuclei along the same axis. We could detect asymmetric changes of the nucleus associated with modification of nucleolar size. Stereotypical modification of the nucleus toward the nucleolus further confirmed the asymmetric properties of the nuclear envelope.

Summary: This novel method to explore 3D geometry of the nuclear envelope with enhanced resolution and post-acquisition correction of z-axis aberration revealed increased NPC density near the SPB and the nucleolus.

Potential role of Apoptosis Inducing Factor in evolutionarily significant eukaryote, Dictyostelium discoideum survival

Apoptosis Inducing Factor (AIF), a phylogenetically conserved mitochondrial inter-membrane space flavoprotein has an important role in caspase independent cell death. Nevertheless, AIF is also essential for cell survival. It is required for mitochondrial organization and energy metabolism. Upon apoptotic stimulation, AIF induces DNA fragmentation after its mitochondrio-nuclear translocation. Although it executes critical cellular functions in a coordinated manner, the exact mechanism still remains obscure. The present study aims to understand AIF's role in cell survival, growth and development by its down-regulation in an interesting unicellular eukaryote, D. discoideum which exhibits multicellularity upon starvation. Constitutive AIF down-regulated (dR) cells exhibited slower growth and delayed developmental morphogenesis. Also, constitutive AIF dR cells manifested high intracellular ROS, oxidative DNA damage and calcium levels with lower ATP content. Interestingly, constitutive AIF dR cells showed amelioration in cell growth upon antioxidant treatment, strengthening its role as ROS regulator. Under oxidative stress, AIF dR cells showed early mitochondrial membrane depolarization followed by AIF translocation from mitochondria to nucleus and exhibited necrotic cell death as compared to paraptoptic cell death of control cells. Thus, the results of this study provide an exemplar where AIF is involved in growth and development by regulating ROS levels and maintaining mitochondrial function in D. discoideum, an evolutionarily significant model organism exhibiting caspase independent apoptosis.

A mitotic nuclear envelope tether for Gle1 also impacts nuclear and nucleolar architecture

During Aspergillus nidulans mitosis peripheral nuclear pore complex (NPC) proteins (Nups) disperse from the core NPC structure. Unexpectedly, one predicted peripheral Nup, Gle1, remains at the mitotic NE via an unknown mechanism. Gle1 affinity purification identified MtgA ( M: itotic T: ether for G: le1), which tethers Gle1 to the NE during mitosis, but not during interphase when Gle1 is at NPCs. MtgA is the ortholog of the Schizosaccharomyces pombe telomere-anchoring inner nuclear membrane protein Bqt4. Like Bqt4, MtgA has meiotic roles but is functionally distinct from Bqt4 as MtgA is not required for tethering telomeres to the NE. Domain analyses revealed MtgA targeting to the NE requires its C-terminal transmembrane domain and a nuclear localization signal. Importantly, MtgA functions beyond Gle1 mitotic targeting and meiosis and impacts nuclear and nucleolar architecture when deleted or overexpressed. Deletion of MtgA generates small, round nuclei whereas overexpressing MtgA generates larger nuclei with altered nuclear compartmentalization resulting from NE expansion around the nucleolus. The accumulation of MtgA around the nucleolus promotes a similar accumulation of the endoplasmic reticulum (ER) protein Erg24 lowering its levels in the ER. This study extends the functions of Bqt4-like proteins to include mitotic Gle1 targeting and modulation of nuclear and nucleolar architecture.

Nicotinamide supplementation phenocopies SIR2 inactivation by modulating carbon metabolism and respiration during yeast chronological aging

Nicotinamide (NAM), a form of vitamin B₃, is a byproduct and noncompetitive inhibitor of the deacetylation reaction catalyzed by Sirtuins. These represent a family of evolutionarily conserved NAD⁺-dependent deacetylases that are well-known critical regulators of metabolism and aging and whose founding member is Sir2 of Saccharomyces cerevisiae. Here, we investigated the effects of NAM supplementation in the context of yeast chronological aging, the established model for studying aging of postmitotic quiescent mammalian cells. Our data show that NAM supplementation at the diauxic shift results in a phenocopy of chronologically aging sir2Δ cells. In fact, NAM-supplemented cells display the same chronological lifespan extension both in expired medium and extreme Calorie Restriction. Furthermore, NAM allows the cells to push their metabolism toward the same outcomes of sir2Δ cells by elevating the level of the acetylated Pck1. Both these cells have the same metabolic changes that concern not only anabolic pathways such as an increased gluconeogenesis but also respiratory activity in terms both of respiratory rate and state of respiration. In particular, they have a higher respiratory reserve capacity and a lower non-phosphorylating respiration that in concert with a low burden of superoxide anions can affect positively chronological aging.

Poly (ADP-ribose) polymerase1 regulates growth and multicellularity in D. discoideum

Poly (ADP-ribose) polymerase (PARP)-1 regulates various biological processes like DNA repair, cell death etc. However, the role of PARP-1 in growth and differentiation still remains elusive. The present study has been undertaken to understand the role of PARP-1 in growth and development of a unicellular eukaryote, Dictyostelium discoideum. In silico analysis demonstrates ADPRT1A as the ortholog of human PARP-1 in D. discoideum. The present study shows that ADPRT1A overexpression (A OE) led to slow growth of D. discoideum and significant population of AOE cells were in S and G2/M phase. Also, AOE cells exhibited high endogenous PARP activity, significant NAD(+) depletion and also significantly lower ADPRT1B and ADPRT2 transcript levels. Moreover, AOE cells are intrinsically stressed and also exhibited susceptibility to oxidative stress. AOE also affected development of D. discoideum predominantly streaming, aggregation and formation of early culminant which are concomitant with reports on PARP's role in D. discoideum development. In addition, under developmental stimuli, increased PARP activity was seen along with developmentally regulated transcript levels of ADPRT1A during D. discoideum multicellularity. Thus the present study suggests that PARP-1 regulates growth as well as the developmental morphogenesis of D. discoideum, thereby opening new avenues to understand the same in higher eukaryotes.

Temporal Regulation of Lipin Activity Diverged to Account for Differences in Mitotic Programs

Eukaryotes remodel the nucleus during mitosis using a variety of mechanisms that differ in the timing and the extent of nuclear envelope (NE) breakdown. Here, we probe the principles enabling this functional diversity by exploiting the natural divergence in NE management strategies between the related fission yeasts Schizosaccharomyces pombe and Schizosaccharomyces japonicus [1-3]. We show that inactivation of Ned1, the phosphatidic acid phosphatase of the lipin family, by CDK phosphorylation is both necessary and sufficient to promote NE expansion required for "closed" mitosis in S. pombe. In contrast, Ned1 is not regulated during division in S. japonicus, thus limiting membrane availability and necessitating NE breakage. Interspecies gene swaps result in phenotypically normal divisions with the S. japonicus lipin acquiring an S. pombe-like mitotic phosphorylation pattern. Our results provide experimental evidence for the mitotic regulation of phosphatidic acid flux and suggest that the regulatory networks governing lipin activity diverged in evolution to give rise to strikingly dissimilar mitotic programs.

Nuclear localization and functional characteristics of voltage-gated potassium channel Kv1.3

It is widely known that ion channels are expressed in the plasma membrane. However, a few studies have suggested that several ion channels including voltage-gated K(+) (Kv) channels also exist in intracellular organelles where they are involved in the biochemical events associated with cell signaling. In the present study, Western blot analysis using fractionated protein clearly indicates that Kv1.3 channels are expressed in the nuclei of MCF7, A549, and SNU-484 cancer cells and human brain tissues. In addition, Kv1.3 is located in the plasma membrane and the nucleus of Jurkat T cells. Nuclear membrane hyperpolarization after treatment with margatoxin (MgTX), a specific blocker of Kv1.3 channels, provides evidence for functional channels at the nuclear membrane of A549 cells. MgTX-induced hyperpolarization is abolished in the nuclei of Kv1.3 silenced cells, and the effects of MgTX are dependent on the magnitude of the K(+) gradient across the nuclear membrane. Selective Kv1.3 blockers induce the phosphorylation of cAMP response element-binding protein (CREB) and c-Fos activation. Moreover, Kv1.3 is shown to form a complex with the upstream binding factor 1 in the nucleus. Chromatin immunoprecipitation assay reveals that Sp1 transcription factor is directly bound to the promoter region of the Kv1.3 gene, and the Sp1 regulates Kv1.3 expression in the nucleus of A549 cells. These results demonstrate that Kv1.3 channels are primarily localized in the nucleus of several types of cancer cells and human brain tissues where they are capable of regulating nuclear membrane potential and activation of transcription factors, such as phosphorylated CREB and c-Fos.

Minimization of extracellular space as a driving force in prokaryote association and the origin of eukaryotes

BACKGROUND

Internalization-based hypotheses of eukaryotic origin require close physical association of host and symbiont. Prior hypotheses of how these associations arose include chance, specific metabolic couplings between partners, and prey-predator/parasite interactions. Since these hypotheses were proposed, it has become apparent that mixed-species, close-association assemblages (biofilms) are widespread and predominant components of prokaryotic ecology. Which forces drove prokaryotes to evolve the ability to form these assemblages are uncertain. Bacteria and archaea have also been found to form membrane-lined interconnections (nanotubes) through which proteins and RNA pass. These observations, combined with the structure of the nuclear envelope and an energetic benefit of close association (see below), lead us to propose a novel hypothesis of the driving force underlying prokaryotic close association and the origin of eukaryotes.

RESULTS

Respiratory proton transport does not alter external pH when external volume is effectively infinite. Close physical association decreases external volume. For small external volumes, proton transport decreases external pH, resulting in each transported proton increasing proton motor force to a greater extent. We calculate here that in biofilms this effect could substantially decrease how many protons need to be transported to achieve a given proton motor force. Based as it is solely on geometry, this energetic benefit would occur for all prokaryotes using proton-based respiration.

CONCLUSIONS

This benefit may be a driving force in biofilm formation. Under this hypothesis a very wide range of prokaryotic species combinations could serve as eukaryotic progenitors. We use this observation and the discovery of prokaryotic nanotubes to propose that eukaryotes arose from physically distinct, functionally specialized (energy factory, protein factory, DNA repository/RNA factory), obligatorily symbiotic prokaryotes in which the protein factory and DNA repository/RNA factory cells were coupled by nanotubes and the protein factory ultimately internalized the other two. This hypothesis naturally explains many aspects of eukaryotic physiology, including the nuclear envelope being a folded single membrane repeatedly pierced by membrane-bound tubules (the nuclear pores), suggests that species analogous or homologous to eukaryotic progenitors are likely unculturable as monocultures, and makes a large number of testable predictions.

REVIEWERS

This article was reviewed by Purificación López-García and Toni Gabaldón.

Rewiring yeast acetate metabolism through MPC1 loss of function leads to mitochondrial damage and decreases chronological lifespan

During growth on fermentable substrates, such as glucose, pyruvate, which is the end-product of glycolysis, can be used to generate acetyl-CoA in the cytosol via acetaldehyde and acetate, or in mitochondria by direct oxidative decarboxylation. In the latter case, the mitochondrial pyruvate carrier (MPC) is responsible for pyruvate transport into mitochondrial matrix space. During chronological aging, yeast cells which lack the major structural subunit Mpc1 display a reduced lifespan accompanied by an age-dependent loss of autophagy. Here, we show that the impairment of pyruvate import into mitochondria linked to Mpc1 loss is compensated by a flux redirection of TCA cycle intermediates through the malic enzyme-dependent alternative route. In such a way, the TCA cycle operates in a “branched” fashion to generate pyruvate and is depleted of intermediates. Mutant cells cope with this depletion by increasing the activity of glyoxylate cycle and of the pathway which provides the nucleocytosolic acetyl-CoA. Moreover, cellular respiration decreases and ROS accumulate in the mitochondria which, in turn, undergo severe damage. These acquired traits in concert with the reduced autophagy restrict cell survival of the mpc1∆ mutant during chronological aging. Conversely, the activation of the carnitine shuttle by supplying acetyl-CoA to the mitochondria is sufficient to abrogate the short-lived phenotype of the mutant.

Involvement of poly(ADP-ribose) polymerase in paraptotic cell death of D. discoideum

Paraptosis is mediated by several proteins, poly(ADP-ribose) polymerase being one of them. D. discoideum lacks caspases thus providing a better system to dissect out the role of PARP in paraptosis. The cell death phenotype in unicellular eukaryote, D. discoideum is similar to the programmed cell death phenotype of multicellular animals. However, the events downstream to the death signal of PCD in D. discoideum are yet to be understood. Our results emphasize that oxidative stress in D. discoideum lacking caspases leads to PARP activation, mitochondrial membrane potential changes, followed by the release of apoptosis inducing factor from mitochondria. AIF causes large scale DNA fragmentation, a hallmark feature of paraptosis. The role of PARP in paraptosis is reiterated via PARP inhibition by benzamide, PARG inhibition by gallotannin and PARP down-regulation, which delays paraptosis. PARP, PARG and AIF interplay is quintessential in paraptosis of D. discoideum. This is the first report to establish the involvement of PARP in the absence of caspase activity in D. discoideum which could be of evolutionary significance and gives a lead to understand the caspase independent paraptotic mechanism in higher organisms.

The mitochondrial Ras-related GTPase Miro: views from inside and outside the metazoan kingdom

Miro GTPase, a member of the Ras superfamily, consists of two GTPase domains flanking a pair of EF hand motifs and a C-terminal transmembrane domain that anchors the protein to the mitochondrial outer membrane. Since the identification of Miro in humans, a series of studies in metazoans, including mammals and fruit flies, have shown that Miro plays a role in the calcium-dependent regulation of mitochondrial transport along microtubules. However, in non-metazoans, including yeasts, slime molds, and plants, Miro is primarily involved in the maintenance of mitochondrial morphology and homeostasis. Given the high level of conservation of Miro in eukaryotes and the variation in the molecular mechanisms of mitochondrial transport between eukaryotic lineages, Miro may have a common ancestral function in mitochondria, and its roles in the regulation of mitochondrial transport may have been acquired specifically by metazoans after the evolutionary divergence of eukaryotes.

Proteases involved during oxidative stress-induced poly(ADP-ribose) polymerase-mediated cell death in Dictyostelium discoideum

Apoptosis involves a cascade of caspase activation leading to the ordered dismantling of critical cell components. However, little is known about the dismantling process in non-apoptotic cell death where caspases are not involved. Dictyostelium discoideum is a good model system to study caspase-independent cell death where experimental accessibility of non-apoptotic cell death is easier and molecular redundancy is reduced compared with other animal models. Poly(ADP-ribose) polymerase (PARP) is one of the key players in cell death. We have previously reported the role of PARP in development and the oxidative stress-induced cell death of D. discoideum. D. discoideum possesses nine PARP genes and does not have a caspase gene, and thus it provides a better model system to dissect the role of PARP in caspase-independent cell death. The current study shows that non-apoptotic cell death in D. discoideum occurs in a programmed fashion where proteases cause mitochondrial membrane potential changes followed by plasma membrane rupture and early loss of plasma membrane integrity. Furthermore, the results suggest that calpains and cathepsin D, which are instrumental in dismantling the cell, act downstream of PARP. Thus, PARP, apoptosis inducing factor, calpains and cathepsin D are the key players in D. discoideum caspase-independent cell death, acting in a sequential manner.

The sub-cellular localisation of the potato (Solanum tuberosum L.) carotenoid biosynthetic enzymes, CrtRb2 and PSY2

Carotenoids are isoprenoids with important biological roles both for plants and animals. The yellow flesh colour of potato (Solanum tuberosum L.) tubers is a quality trait dependent on the types and levels of carotenoids that accumulate. The carotenoid biosynthetic pathway is well characterised, facilitating the successful engineering of carotenoid content in numerous crops including potato. However, a clear understanding concerning the factors regulating carotenoid accumulation and localisation in plant storage organs, such as tubers, is lacking. In the present study, the localisation of key carotenoid biosynthetic enzymes was investigated, as one of the unexplored factors that could influence the accumulation of carotenoids in potato tubers. Stable transgenic potato plants were generated by over-expressing β-CAROTENE HYDROXYLASE 2 (CrtRb2) and PHYTOENE SYNTHASE 2 (PSY2) genes, fused to red fluorescent protein (RFP). Gene expression and carotenoid levels were both significantly increased, confirming functionality of the fluorescently tagged proteins. Confocal microscopy studies revealed different sub-organellar localisations of CrtRb2-RFP and PSY2-RFP within amyloplasts. CrtRb2 was detected in small vesicular structures, inside amyloplasts, whereas PSY2 was localised in the stroma of amyloplasts. We conclude that it is important to consider the location of biosynthetic enzymes when engineering the carotenoid metabolic pathway in storage organs such as tubers.

Defects associated with mitochondrial DNA damage can be mitigated by increased vacuolar pH in Saccharomyces cerevisiae

While searching for mutations that alleviate detrimental effects of mitochondrial DNA (mtDNA) damage, we found that disrupting vacuolar biogenesis permitted survival of a sensitized yeast background after mitochondrial genome loss. Furthermore, elevating vacuolar pH increases proliferation after mtDNA deletion and reverses the protein import defect of mitochondria lacking DNA.

Dietary restriction and mitochondrial function link replicative and chronological aging in Saccharomyces cerevisiae

Chronological aging of budding yeast cells results in a reduction in subsequent replicative life span through unknown mechanisms. Here we show that dietary restriction during chronological aging delays the reduction in subsequent replicative life span up to at least 23days of chronological age. We further show that among the viable portion of the control population aged 26days, individual cells with the lowest mitochondrial membrane potential have the longest subsequent replicative lifespan. These observations demonstrate that dietary restriction modulates a common molecular mechanism linking chronological and replicative aging in yeast and indicate a critical role for mitochondrial function in this process.