The glutathione system maintains the thiol redox balance in the mitochondria of fission yeast

The thioredoxin and glutathione (GSH)-glutaredoxin electron donor pathways provide a reducing environment to the cell and maintain homeostasis of numerous redox reactions. The abundant tripeptide GSH has multiple roles, including redox buffering, detoxification, peroxide scavenging and iron-sulfur cluster assembly. Glutathione reductase, Pgr1 in fission yeast, maintains glutathione reduced, and it is essential in most organisms. Cells lacking Pgr1 exhibit severe pleiotropic defects. We used multiple approaches to unravel the compartment-specific roles of Pgr1. Our findings confirmed that Pgr1 had dual cytosolic and mitochondrial localization. Mitochondrial homeostasis was severely impaired in Δpgr1 cells and most of these defects were restored by expression of an exclusively mitochondrial Pgr1 isoform. As expected, the cytosol of Δpgr1 cells showed low ratio of reduced-to-oxidized glutathione. However, this did not significantly affect peroxiredoxin-dependent hydrogen peroxide scavenging, suggesting a minimal role, if any, of GSH in cytosolic thiol reduction. The transcriptome of Δpgr1 cells revealed signatures of oxidative stress and iron deprivation, suggesting that the GSH-containing sensor of iron starvation, the glutaredoxin Grx4, is also a sensor of GSH oxidation. In the mitochondria, Pgr1 not only provided the GSH electron donor for the glutaredoxin-based pathway but also recycled mitochondrial Trx2, thereby contributing to thiol redox homeostasis in the matrix. In conclusion, glutathione reductase is essential for maintaining a balanced redox environment in the mitochondria by recycling Trx2, Grx2 and the GSH-containing Grx5, and therefore contributes to the processes of iron-sulfur cluster assembly and respiration, while controlling Grx4 dynamics in the cytosol.

The deletion of ppr2 interferes iron sensing and leads to oxidative stress response in Schizosaccharomyces pombe

Pentatricopeptide repeat proteins are involved in mitochondrial both transcriptional and posttranscriptional regulation. Schizosaccharomyces pombe Ppr2 is a general mitochondrial translation factor that plays a critical role in the synthesis of all mitochondrial DNA-encoded oxidative phosphorylation subunits, which are essential for mitochondrial respiration. Our previous analysis showed that ppr2 deletion resulted in increased expression of iron uptake genes and caused ferroptosis-like cell death in S. pombe. In the present work, we showed that deletion of ppr2 reduced viability on glycerol- and galactose-containing media.Php4 is a transcription repressor that regulates iron homeostasis in fission yeast. We found that in the ppr2 deletion strain, Php4 was constitutively active and accumulated in the nucleus in the stationary phase. We also found that deletion of ppr2 decreased the ferroptosis-related protein Gpx1 in the mitochondria. Overexpression of Gpx1 improves the viability of Δppr2 cells. We showed that the deletion of ppr2 increased the production of ROS, downregulated heme synthesis and iron-sulfur cluster proteins, and induced stress proteins. Finally, we observed the nuclear accumulation of Pap1-GFP and Sty1-GFP, suggesting that Sty1 and Pap1 in response to cellular stress in the ppr2 deletion strain. These results suggest thatppr2 deletion may cause mitochondrial dysfunction, which is likely to lead to iron-sensing defect and iron starvation response, resulting in perturbation of iron homeostasis and increased hydroxyl radical production. The increased hydroxyl radical production triggers cellular responses in theppr2 deletion strain.

Identification of novel coenzyme Q10 biosynthetic proteins Coq11 and Coq12 in Schizosaccharomyces pombe

Coenzyme Q (CoQ) is an essential component of the electron transport system in aerobic organisms. CoQ10 has ten isoprene units in its quinone structure and is especially valuable as a food supplement. However, the CoQ biosynthetic pathway has not been fully elucidated, including synthesis of the p-hydroxybenzoic acid (PHB) precursor to form a quinone backbone. To identify the novel components of CoQ10 synthesis, we investigated CoQ10 production in 400 Schizosaccharomyces pombe gene-deleted strains in which individual mitochondrial proteins were lost. We found that deletion of coq11 (an S. cerevisiae COQ11 homolog) and a novel gene designated coq12 lowered CoQ levels to ∼4% of that of the WT strain. Addition of PHB or p-hydroxybenzaldehyde restored the CoQ content and growth and lowered hydrogen sulfide production of the Δcoq12 strain, but these compounds did not affect the Δcoq11 strain. The primary structure of Coq12 has a flavin reductase motif coupled with an NAD+ reductase domain. We determined that purified Coq12 protein from S. pombe displayed NAD+ reductase activity when incubated with ethanol-extracted substrate of S. pombe. Because purified Coq12 from Escherichia coli did not exhibit reductase activity under the same conditions, an extra protein is thought to be necessary for its activity. Analysis of Coq12-interacting proteins by LC-MS/MS revealed interactions with other Coq proteins, suggesting formation of a complex. Thus, our analysis indicates that Coq12 is required for PHB synthesis, and it has diverged among species.

Response to sulfur in Schizosaccharomyces pombe

Sulfur is an essential component of various biologically important molecules, including methionine, cysteine and glutathione, and it is also involved in coping with oxidative and heavy metal stress. Studies using model organisms, including budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe), have contributed not only to understanding various cellular processes but also to understanding the utilization and response mechanisms of each nutrient, including sulfur. Although fission yeast can use sulfate as a sulfur source, its sulfur metabolism pathway is slightly different from that of budding yeast because it does not have a trans-sulfuration pathway. In recent years, it has been found that sulfur starvation causes various cellular responses in S. pombe, including sporulation, cell cycle arrest at G₂, chronological lifespan extension, autophagy induction and reduced translation. This MiniReview identifies two sulfate transporters in S. pombe, Sul1 (encoded by SPBC3H7.02) and Sul2 (encoded by SPAC869.05c), and summarizes the metabolic pathways of sulfur assimilation and cellular response to sulfur starvation. Understanding these responses, including metabolism and adaptation, will contribute to a better understanding of the various stress and nutrient starvation responses and chronological lifespan regulation caused by sulfur starvation.

Benzoic acid inhibits Coenzyme Q biosynthesis in Schizosaccharomyces pombe

Coenzyme Q (CoQ, ubiquinone) is an essential component of the electron transport system in aerobic organisms. Human type CoQ₁₀, which has 10 units of isoprene in its quinone structure, is especially valuable as a food supplement. Therefore, studying the biosynthesis of CoQ₁₀ is important not only for increasing metabolic knowledge, but also for improving biotechnological production. Herein, we show that Schizosaccharomyces pombe utilizes p-aminobenzoate (PABA) in addition to p-hydroxybenzoate (PHB) as a precursor for CoQ₁₀ synthesis. We explored compounds that affect the synthesis of CoQ₁₀ and found benzoic acid (Bz) at >5 μg/mL inhibited CoQ biosynthesis without accumulation of apparent CoQ intermediates. This inhibition was counteracted by incubation with a 10-fold lower amount of PABA or PHB. Overexpression of PHB-polyprenyl transferase encoded by ppt1 (coq2) also overcame the inhibition of CoQ biosynthesis by Bz. Inhibition by Bz was efficient in S. pombe and Schizosaccharomyces japonicus, but less so in Saccharomyces cerevisiae, Aureobasidium pullulans, and Escherichia coli. Bz also inhibited a S. pombe ppt1 (coq2) deletion strain expressing human COQ2, and this strain also utilized PABA as a precursor of CoQ₁₀. Thus, Bz is likely to inhibit prenylation reactions involving PHB or PABA catalyzed by Coq2.

The Fission Yeast RNA-Binding Protein Meu5 Is Involved in Outer Forespore Membrane Breakdown during Spore Formation

In Schizosaccharomyces pombe, the spore wall confers strong resistance against external stress. During meiosis II, the double-layered intracellular forespore membrane (FSM) forms de novo and encapsulates the nucleus. Eventually, the inner FSM layer becomes the plasma membrane of the spore, while the outer layer breaks down. However, the molecular mechanism and biological significance of this membrane breakdown remain unknown. Here, by genetic investigation of an S. pombe mutant (E22) with normal prespore formation but abnormal spores, we showed that Meu5, an RNA-binding protein known to bind to and stabilize more than 80 transcripts, is involved in this process. We confirmed that the E22 mutant does not produce Meu5 protein, while overexpression of meu5⁺ in E22 restores the sporulation defect. Furthermore, electron microscopy revealed that the outer membrane of the FSM persisted in meu5∆ spores. Investigation of the target genes of meu5⁺ showed that a mutant of cyc1⁺ encoding cytochrome c also showed a severe defect in outer FSM breakdown. Lastly, we determined that outer FSM breakdown occurs coincident with or after formation of the outermost Isp3 layer of the spore wall. Collectively, our data provide novel insights into the molecular mechanism of spore formation.

CoQ10 production in Schizosaccharomyces pombe is increased by reduction of glucose levels or deletion of pka1

Coenzyme Q (CoQ) is an essential component of the electron transport system that produces ATP in nearly all living cells. CoQ₁₀ is a popular commercial food supplement around the world, and demand for efficient production of this molecule has increased in recent years. In this study, we explored CoQ₁₀ production in the fission yeast Schizosaccharomyces pombe. We found that CoQ₁₀ level was higher in stationary phase than in log phase, and that it increased when the cells were grown in a low concentration of glucose, in maltose, or in glycerol/ethanol medium. Because glucose signaling is mediated by cAMP, we evaluated the involvement of this pathway in CoQ biosynthesis. Loss of Pka1, the catalytic subunit of cAMP-dependent protein kinase, increased production of CoQ₁₀, whereas loss of the regulatory subunit Cgs1 decreased production. Manipulation of other components of the cAMP-signaling pathway affected CoQ₁₀ production in a consistent manner. We also found that glycerol metabolism was controlled by the cAMP/PKA pathway. CoQ₁₀ production by the S. pombe ∆pka1 reached 0.98 mg/g dry cell weight in medium containing a non-fermentable carbon source [2% glycerol (w/v) and 1% ethanol (w/v) supplemented with 0.5% casamino acids (w/v)], twofold higher than the production in wild-type cells under normal growth conditions. These findings demonstrate that carbon source, growth phase, and the cAMP-signaling pathway are important factors in CoQ₁₀ production in S. pombe.

Crystal structure and functional analysis of human C1ORF123

Proteins of the DUF866 superfamily are exclusively found in eukaryotic cells. A member of the DUF866 superfamily, C1ORF123, is a human protein found in the open reading frame 123 of chromosome 1. The physiological role of C1ORF123 is yet to be determined. The only available protein structure of the DUF866 family shares just 26% sequence similarity and does not contain a zinc binding motif. Here, we present the crystal structure of the recombinant human C1ORF123 protein (rC1ORF123). The structure has a 2-fold internal symmetry dividing the monomeric protein into two mirrored halves that comprise of distinct electrostatic potential. The N-terminal half of rC1ORF123 includes a zinc-binding domain interacting with a zinc ion near to a potential ligand binding cavity. Functional studies of human C1ORF123 and its homologue in the fission yeast Schizosaccharomyces pombe (SpEss1) point to a role of DUF866 protein in mitochondrial oxidative phosphorylation.

Studying anti-oxidative properties of inclusion complexes of α-lipoic acid with γ-cyclodextrin in single living fission yeast by confocal Raman microspectroscopy

α-lipoic acid (ALA) is an essential cofactor for many enzyme complexes in aerobic metabolism, especially in mitochondria of eukaryotic cells where respiration takes place. It also has excellent anti-oxidative properties. The acid has two stereo-isomers, R- and S- lipoic acid (R-LA and S-LA), but only the R-LA has biological significance and is exclusively produced in our body. A mutant strain of fission yeast, Δdps1, cannot synthesize coenzyme Q10, which is essential during yeast respiration, leading to oxidative stress. Therefore, it shows growth delay in the minimal medium. We studied anti-oxidant properties of ALA in its free form and their inclusion complexes with γ-cyclodextrin using this mutant yeast model. Both free forms R- and S-LA as well as 1:1 inclusion complexes with γ-cyclodextrin recovered growth of Δdps1 depending on the concentration and form. However, it has no effect on the growth of wild type fission yeast strain at all. Raman microspectroscopy was employed to understand the anti-oxidant property at the molecular level. A sensitive Raman band at 1602cm^-1 was monitored with and without addition of ALAs. It was found that 0.5mM and 1.0mM concentrations of ALAs had similar effect in both free and inclusion forms. At 2.5mM ALAs, free forms inhibited the growth while inclusion complexes helped in recovered. 5.0mM ALA showed inhibitory effect irrespective of form. Our results suggest that the Raman band at 1602cm^-1 is a good measure of oxidative stress in fission yeast.

Biosynthesis and applications of prenylquinones

Prenylquinones are isoprenoid compounds with a characteristic quinone structure and isoprenyl tail that are ubiquitous in almost all living organisms. There are four major prenylquinone classes: ubiquinone (UQ), menaquinone (MK), plastoquinone (PQ), and rhodoquinone (RQ). The quinone structure and isoprenyl tail length differ among organisms. UQ, PQ, and RQ contain benzoquinone, while MK contains naphthoquinone. UQ, MK, and RQ are involved in oxidative phosphorylation, while PQ functions in photosynthetic electron transfer. Some organisms possess two types of prenylquinones; Escherichia coli has UQ₈ and MK₈, and Caenorhabditis elegans has UQ₉ and RQ₉. Crystal structures of most of the enzymes involved in MK synthesis have been solved. Studies on the biosynthesis and functions of quinones have advanced recently, including for phylloquinone (PhQ), which has a phytyl moiety instead of an isoprenyl tail. Herein, the synthesis and applications of prenylquinones are reviewed.

Schizosaccharomyces japonicus has low levels of CoQ10 synthesis, respiration deficiency, and efficient ethanol production

Coenzyme Q (CoQ) is essential for mitochondrial respiration and as a cofactor for sulfide quinone reductase. Schizosaccharomyces pombe produces a human-type CoQ₁₀. Here, we analyzed CoQ in other fission yeast species. S. cryophilus and S. octosporus produce CoQ₉. S. japonicus produces low levels of CoQ₁₀, although all necessary genes for CoQ synthesis have been identified in its genome. We expressed three genes (dps1, dlp1, and ppt1) for CoQ synthesis from S. japonicus in the corresponding S. pombe mutants, and confirmed that they were functional. S. japonicus had very low levels of oxygen consumption and was essentially respiration defective, probably due to mitochondrial dysfunction. S. japonicus grows well on minimal medium during anaerobic culture, indicating that it acquires sufficient energy by fermentation. S. japonicus produces comparable levels of ethanol under both normal and elevated temperature (42 °C) conditions, at which S. pombe is not able to grow.

A genome-wide screen for FTY720-sensitive mutants reveals genes required for ROS homeostasis

Fingolimod hydrochloride (FTY720), a sphingosine-1-phosphate (S1P) analogue, is an approved immune modulator for the treatment of multiple sclerosis (MS). Notably, in addition to its well-known mode of action as an S1P modulator, accumulating evidence suggests that FTY720 induces apoptosis in various cancer cells via reactive oxygen species (ROS) generation. Although the involvement of multiple signaling molecules, such as JNK (Jun N-terminal kinase), Akt (alpha serine/threonine-protein kinase) and Sphk has been reported, the exact mechanisms how FTY720 induces cell growth inhibition and the functional relationship between FTY720 and these signaling pathways remain elusive. Our previous reports using the fission yeast Schizosaccharomyces pombe as a model system to elucidate FTY720-mediated signaling pathways revealed that FTY720 induces an increase in intracellular Ca²⁺ concentrations and ROS generation, which resulted in the activation of the transcriptional responses downstream of Ca²⁺/calcineurin signaling and stress-activated MAPK signaling, respectively. Here, we performed a genome-wide screening for genes whose deletion induces FTY720-sensitive growth in S. pombe and identified 49 genes. These gene products are related to the biological processes involved in metabolic processes, transport, transcription, translation, chromatin organization, cytoskeleton organization and intracellular signal transduction. Notably, most of the FTY720-sensitive deletion cells exhibited NAC-remedial FTY720 sensitivities and dysregulated ROS homeostasis. Our results revealed a novel gene network involving ROS homeostasis and the possible mechanisms of the FTY720 toxicity.

Biosynthesis of coenzyme Q in eukaryotes

Coenzyme Q (CoQ) is a component of the electron transport chain that participates in aerobic cellular respiration to produce ATP. In addition, CoQ acts as an electron acceptor in several enzymatic reactions involving oxidation-reduction. Biosynthesis of CoQ has been investigated mainly in Escherichia coli and Saccharomyces cerevisiae, and the findings have been extended to various higher organisms, including plants and humans. Analyses in yeast have contributed greatly to current understanding of human diseases related to CoQ biosynthesis. To date, human genetic disorders related to mutations in eight COQ biosynthetic genes have been reported. In addition, the crystal structures of a number of proteins involved in CoQ synthesis have been solved, including those of IspB, UbiA, UbiD, UbiX, UbiI, Alr8543 (Coq4 homolog), Coq5, ADCK3, and COQ9. Over the last decade, knowledge of CoQ biosynthesis has accumulated, and striking advances in related human genetic disorders and the crystal structure of proteins required for CoQ synthesis have been made. This review focuses on the biosynthesis of CoQ in eukaryotes, with some comparisons to the process in prokaryotes.

Production of CoQ10 in fission yeast by expression of genes responsible for CoQ10 biosynthesis

Coenzyme Q10 (CoQ10) is essential for energy production and has become a popular supplement in recent years. In this study, CoQ10 productivity was improved in the fission yeast Schizosaccharomyces pombe. Ten CoQ biosynthetic genes were cloned and overexpressed in S. pombe. Strains expressing individual CoQ biosynthetic genes did not produce higher than a 10% increase in CoQ10 production. In addition, simultaneous expression of all ten coq genes did not result in yield improvements. Genes responsible for the biosynthesis of p-hydroxybenzoate and decaprenyl diphosphate, both of which are CoQ biosynthesis precursors, were also overexpressed. CoQ10 production was increased by overexpression of Eco_ubiC (encoding chorismate lyase), Eco_aroFFBR (encoding 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase), or Sce_thmgr1 (encoding truncated HMG-CoA reductase). Furthermore, simultaneous expression of these precursor genes resulted in two fold increases in CoQ10 production.

Fitness profiling links topoisomerase II regulation of centromeric integrity to doxorubicin resistance in fission yeast

Doxorubicin, a chemotherapeutic agent, inhibits the religation step of topoisomerase II (Top2). However, the downstream ramifications of this action are unknown. Here we performed epistasis analyses of top2 with 63 genes representing doxorubicin resistance (DXR) genes in fission yeast and revealed a subset that synergistically collaborate with Top2 to confer DXR. Our findings show that the chromatin-regulating RSC and SAGA complexes act with Top2 in a cluster that is functionally distinct from the Ino80 complex. In various DXR mutants, doxorubicin hypersensitivity was unexpectedly suppressed by a concomitant top2 mutation. Several DXR proteins showed centromeric localization, and their disruption resulted in centromeric defects and chromosome missegregation. An additional top2 mutation could restore centromeric chromatin integrity, suggesting a counterbalance between Top2 and these DXR factors in conferring doxorubicin resistance. Overall, this molecular basis for mitotic catastrophe associated with doxorubicin treatment will help to facilitate drug combinatorial usage in doxorubicin-related chemotherapeutic regimens.

Functional conservation of coenzyme Q biosynthetic genes among yeasts, plants, and humans

Coenzyme Q (CoQ) is an essential factor for aerobic growth and oxidative phosphorylation in the electron transport system. The biosynthetic pathway for CoQ has been proposed mainly from biochemical and genetic analyses of Escherichia coli and Saccharomyces cerevisiae; however, the biosynthetic pathway in higher eukaryotes has been explored in only a limited number of studies. We previously reported the roles of several genes involved in CoQ synthesis in the fission yeast Schizosaccharomyces pombe. Here, we expand these findings by identifying ten genes (dps1, dlp1, ppt1, and coq3–9) that are required for CoQ synthesis. CoQ10-deficient S. pombe coq deletion strains were generated and characterized. All mutant fission yeast strains were sensitive to oxidative stress, produced a large amount of sulfide, required an antioxidant to grow on minimal medium, and did not survive at the stationary phase. To compare the biosynthetic pathway of CoQ in fission yeast with that in higher eukaryotes, the ability of CoQ biosynthetic genes from humans and plants (Arabidopsis thaliana) to functionally complement the S. pombe coq deletion strains was determined. With the exception of COQ9, expression of all other human and plant COQ genes recovered CoQ10 production by the fission yeast coq deletion strains, although the addition of a mitochondrial targeting sequence was required for human COQ3 and COQ7, as well as A. thaliana COQ6. In summary, this study describes the functional conservation of CoQ biosynthetic genes between yeasts, humans, and plants.

The fission yeast php2 mutant displays a lengthened chronological lifespan

The Schizosaccharomyces pombe php2(+) gene encodes a subunit of the CCAAT-binding factor complex. We found that disruption of the php2(+) gene extended the chronological lifespan of the fission yeast. Moreover, the lifespan of the Δphp2 mutant was barely extended under calorie restricted (CR) conditions. Many other phenotypes of the Δphp2 mutant resembled those of wild-type cells grown under CR conditions, suggesting that the Δphp2 mutant might undergo CR. The mutant also showed low respiratory activity concomitant with decreased expression of the cyc1(+) and rip1(+) genes, both of which are involved in mitochondrial electron transport. On the basis of a chromatin immunoprecipitation assay, we determined that Php2 binds to a DNA region upstream of cyc1(+) and rip1(+) in S. pombe. Here we discuss the possible mechanisms by which the chronological lifespan of Δphp2 mutant is extended.

Polypeptone induces dramatic cell lysis in ura4 deletion mutants of fission yeast

Polypeptone is widely excluded from Schizosaccharomyces pombe growth medium. However, the reasons why polypeptone should be avoided have not been documented. Polypeptone dramatically induced cell lysis in the ura4 deletion mutant when cells approached the stationary growth phase, and this phenotype was suppressed by supplementation of uracil. To determine the specificity of this cell lysis phenotype, we created deletion mutants of other genes involved in de novo biosynthesis of uridine monophosphate (ura1, ura2, ura3, and ura5). Cell lysis was not observed in these gene deletion mutants. In addition, concomitant disruption of ura1, ura2, ura3, or ura5 in the ura4 deletion mutant suppressed cell lysis, indicating that cell lysis induced by polypeptone is specific to the ura4 deletion mutant. Furthermore, cell lysis was also suppressed when the gene involved in coenzyme Q biosynthesis was deleted. This is likely because Ura3 requires coenzyme Q for its activity. The ura4 deletion mutant was sensitive to zymolyase, which mainly degrades (1,3)-beta-D glucan, when grown in the presence of polypeptone, and cell lysis was suppressed by the osmotic stabiliser, sorbitol. Finally, the induction of cell lysis in the ura4 deletion mutant was due to the accumulation of orotidine-5-monophosphate. Cell wall integrity was dramatically impaired in the ura4 deletion mutant when grown in the presence of polypeptone. Because ura4 is widely used as a selection marker in S. pombe, caution needs to be taken when evaluating phenotypes of ura4 mutants.

Dysfunctional Coq9 protein causes predominant encephalomyopathy associated with CoQ deficiency

Coenzyme Q10 (CoQ(10)) or ubiquinone is a well-known component of the mitochondrial respiratory chain. In humans, CoQ(10) deficiency causes a mitochondrial syndrome with an unexplained variability in the clinical presentations. To try to understand this heterogeneity in the clinical phenotypes, we have generated a Coq9 Knockin (R239X) mouse model. The lack of a functional Coq9 protein in homozygous Coq9 mutant (Coq9(X/X)) mice causes a severe reduction in the Coq7 protein and, as consequence, a widespread CoQ deficiency and accumulation of demethoxyubiquinone. The deficit in CoQ induces a brain-specific impairment of mitochondrial bioenergetics performance, a reduction in respiratory control ratio, ATP levels and ATP/ADP ratio and specific loss of respiratory complex I. These effects lead to neuronal death and demyelinization with severe vacuolization and astrogliosis in the brain of Coq9(X/X) mice that consequently die between 3 and 6 months of age. These results suggest that the instability of mitochondrial complex I in the brain, as a primary event, triggers the development of mitochondrial encephalomyopathy associated with CoQ deficiency.

A homeobox protein Phx1 regulates long-term survival and meiotic sporulation in Schizosaccharomyces pombe

BACKGROUND

In the fission yeast Schizosaccharomyces pombe, the phx1+ (pombe homeobox) gene was initially isolated as a multi-copy suppressor of lysine auxotrophy caused by depletion of copper/zinc-containing superoxide dismutase (CuZn-SOD). Overproduction of Phx1 increased the synthesis of homocitrate synthase, the first enzyme in lysine biosynthetic pathway, which is labile to oxidative stress. Phx1 has a well conserved DNA-binding domain called homeodomain at the N-terminal region and is predicted to be a transcription factor in S. pombe. However, its role has not been revealed in further detail. Here we examined its expression pattern and the phenotype of its null mutant to get clues on its function.

RESULTS

Fluorescence from the Phx1-GFP expressed from a chromosomal fusion gene demonstrated that it is localized primarily in the nucleus, and is distinctly visible during the stationary phase. When we replaced the N-terminal homeobox domain of Phx1 with the DNA binding domain of Pap1, a well-characterized transcription factor, the chimeric protein caused the elevation of transcripts from Pap1-dependent genes such as ctt1+ and trr1+, suggesting that Phx1 possesses transcriptional activating activity when bound to DNA. The amount of phx1+ transcripts sharply increased as cells entered the stationary phase and was maintained at high level throughout the stationary phase. Nutrient shift down to low nitrogen or carbon sources caused phx1+ induction during the exponential phase, suggesting that cells need Phx1 for maintenance function during nutrient starvation. The Δphx1 null mutant showed decreased viability in long-term culture, whereas overproduction of Phx1 increased viability. Decrease in long-term survival was also observed for Δphx1 under N- or C-starved conditions. In addition, Δphx1 mutant was more sensitive to various oxidants and heat shock. When we examined sporulation of the Δphx1/Δphx1 diploid strain, significant decrease in the formation of meiotic spores was observed.

CONCLUSIONS

Phx1 is a transcriptional regulator whose synthesis is elevated during stationary phase and by nutrient starvation in S. pombe. It supports long-term survival and stress tolerance against oxidation and heat, and plays a key role in the formation of meiotic spores.

Reversal of slow growth and heartbeat through the restoration of mitochondrial function in clk-1-deficient mouse embryos by exogenous administration of coenzyme Q10

The longevity gene clk-1/coq7 encodes an enzyme that is essential for the biosynthesis of coenzyme Q (CoQ) in mitochondria and regulates the lifespan and behavioral timing in Caenorhabditis elegans and the chronological lifespan in fission yeast. However, whether the mammalian clk-1/coq7 ortholog (clk-1) regulates these phenotypes in mammals remains to be fully evaluated due to the embryonic lethality of clk-1-deficient (clk-1(-/-)) mice. To investigate whether clk-1 regulates biological functions, such as growth and heartbeat, through CoQ in mouse embryos, we cultivated the cells and hearts of clk-1(-/-) mouse embryos at embryonic day 10.5 (E10.5) for at least 10 days in the presence of fetal bovine serum. In embryonic cells, cardiomyocytes, and hearts, the growth and heart rates were significantly slowed in clk-1(-/-) compared with wild-type or heterozygous mouse tissues. Moreover, frequent apoptosis and a significant reduction in mitochondrial functions, including membrane potential and ATP production, were observed in the clk-1(-/-) cells and hearts. The slowed growth and heart rates and the reduced mitochondrial function of clk-1(-/-) embryonic cells and hearts in culture were almost completely rescued by the administration of exogenous CoQ(10). The results indicate that clk-1 regulates growth and heart rates through CoQ-mediated mitochondrial functions in mouse embryos.

Effects of inhibiting CoQ10 biosynthesis with 4-nitrobenzoate in human fibroblasts

Coenzyme Q(10) (CoQ(10)) is a potent lipophilic antioxidant in cell membranes and a carrier of electrons in the mitochondrial respiratory chain. We previously characterized the effects of varying severities of CoQ(10) deficiency on ROS production and mitochondrial bioenergetics in cells harboring genetic defects of CoQ(10) biosynthesis. We observed a unimodal distribution of ROS production with CoQ(10) deficiency: cells with <20% of CoQ(10) and 50-70% of CoQ(10) did not generate excess ROS while cells with 30-45% of CoQ(10) showed increased ROS production and lipid peroxidation. Because our previous studies were limited to a small number of mutant cell lines with heterogeneous molecular defects, here, we treated 5 control and 2 mildly CoQ(10) deficient fibroblasts with varying doses of 4-nitrobenzoate (4-NB), an analog of 4-hydroxybenzoate (4-HB) and inhibitor of 4-para-hydroxybenzoate:polyprenyl transferase (COQ2) to induce a range of CoQ(10) deficiencies. Our results support the concept that the degree of CoQ(10) deficiency in cells dictates the extent of ATP synthesis defects and ROS production and that 40-50% residual CoQ(10) produces maximal oxidative stress and cell death.

The abc1-/coq8- respiratory-deficient mutant of Schizosaccharomyces pombe suffers from glutathione underproduction and hyperaccumulates Cd2+

The abc1(-)/coq8(-) gene deletion respiratory-deficient mutant NBp17 of fission yeast Schizosaccharomyces pombe displayed a phenotypic fermentation pattern with enhanced production of glycerol and acetate, and also possessed oxidative stress-sensitive phenotypes to H(2)O(2), menadione, tBuOOH, Cd(2+), and chromate in comparison with its parental respiratory-competent strain HNT. As a consequence of internal stress-inducing mutation, adaptation processes to restore the redox homeostasis of mutant NBp17 cells were detected in minimal glucose medium. Mutant NBp17 produced significantly increased amounts of O(2)•- and H(2)O(2) as a result of the decreased internal glutathione concentration and the only slightly increased glutathione reductase activity. The Cr(VI) reduction capacity and hence the •OH production ability were decreased. The mutant cells demonstrated increased specific activities of superoxide dismutases and glutathione reductase (but not catalase) to detoxify at least partially the overproduction of reactive oxygen species. All these features may be explained by the decreased redox capacity of the mutant cells. Most notably, mutant NBp17 hyperaccumulated yellow CdS.

Association between genetic variants in the Coenzyme Q10 metabolism and Coenzyme Q10 status in humans

BACKGROUND

Coenzyme Q10 (CoQ10) is essential for mitochondrial energy production and serves as an antioxidants in extra mitochondrial membranes. The genetics of primary CoQ10 deficiency has been described in several studies, whereas the influence of common genetic variants on CoQ10 status is largely unknown. Here we tested for non-synonymous single-nucleotidepolymorphisms (SNP) in genes involved in the biosynthesis (CoQ3G272S , CoQ6M406V, CoQ7M103T), reduction (NQO1P187S, NQO2L47F) and metabolism (apoE3/4) of CoQ10 and their association with CoQ10 status. For this purpose, CoQ10 serum levels of 54 healthy male volunteers were determined before (T0) and after a 14 days supplementation (T14) with 150 mg/d of the reduced form of CoQ10.

FINDINGS

At T0, the CoQ10 level of heterozygous NQO1P187S carriers were significantly lower than homozygous S/S carriers (0.93 ± 0.25 μM versus 1.34 ± 0.42 μM, p = 0.044). For this polymorphism a structure homology-based method (PolyPhen) revealed a possibly damaging effect on NQO1 protein activity. Furthermore, CoQ10 plasma levels were significantly increased in apoE4/E4 genotype after supplementation in comparison to apoE2/E3 genotype (5.93 ± 0.151 μM versus 4.38 ± 0.792 μM, p = 0.034). Likewise heterozygous CoQ3G272S carriers had higher CoQ10 plasma levels at T14 compared to G/G carriers but this difference did not reach significance (5.30 ± 0.96 μM versus 4.42 ± 1.67 μM, p = 0.082).

CONCLUSIONS

In conclusion, our pilot study provides evidence that NQO1P187S and apoE polymorphisms influence CoQ10 status in humans.

Global fitness profiling of fission yeast deletion strains by barcode sequencing

A genome-wide deletion library is a powerful tool for probing gene functions and one has recently become available for the fission yeast Schizosaccharomyces pombe. Here we use deep sequencing to accurately characterize the barcode sequences in the deletion library, thus enabling the quantitative measurement of the fitness of fission yeast deletion strains by barcode sequencing.

Simple and effective gap-repair cloning using short tracts of flanking homology in fission yeast

Gap-repair cloning for plasmid construction in budding yeast is very effective and often used. In contrast, the same method is not widely used in fission yeast, because of a shortage of information on it. Here we describe simple and effective gap-repair cloning for plasmid construction using short tracts of flanking homology. By this method, we combined concentrated DNA fragments with short (20 bp) tracts of flanking homology with the marker gene or the pre-existing gene module. In addition, we found that this method can be applied to one-step cloning of multiple DNA fragments to construct a fusion gene.

Identification of Ecl family genes that extend chronological lifespan in fission yeast

In fission yeast, we identified two genes, named ecl2+ and ecl3+, that are paralogous to ecl1+, which extends the chronological lifespan. Both ecl2+ and ecl3+ extend the chronological lifespan when overexpressed as ecl1+. ecl2+ and ecl3+ encode 84- and 89-amino acid polypeptides respectively that are not annotated in the current database. The Ecl2 protein is localized mainly in the nucleus, as Ecl1. These results suggest that ecl1+, ecl2+, and ecl3+ have overlapping functions in the regulation of chronological lifespan.