Identification of a novel protein kinase that affects the chronological lifespan in fission yeast

Low-Molecular Weight Compounds that Extend the Chronological Lifespan of Yeasts, Saccharomyces cerevisiae, and Schizosaccharomyces pombe

Yeast is an excellent model organism for research for regulating aging and lifespan, and the studies have made many contributions to date, including identifying various factors and signaling pathways related to aging and lifespan. More than 20 years have passed since molecular biological perspectives are adopted in this research field, and intracellular factors and signal pathways that control aging and lifespan have evolutionarily conserved from yeast to mammals. Furthermore, these findings have been applied to control the aging and lifespan of various model organisms by adjustment of the nutritional environment, genetic manipulation, and drug treatment using low-molecular weight compounds. Among these, drug treatment is easier than the other methods, and research into drugs that regulate aging and lifespan is consequently expected to become more active. Chronological lifespan, a definition of yeast lifespan, refers to the survival period of a cell population under nondividing conditions. Herein, low-molecular weight compounds are summarized that extend the chronological lifespan of Saccharomyces cerevisiae and Schizosaccharomyces pombe, along with their intracellular functions. The low-molecular weight compounds are also discussed that extend the lifespan of other model organisms. Compounds that have so far only been studied in yeast may soon extend lifespan in other organisms.

Identification of plb1 mutation that extends longevity via activating Sty1 MAPK in Schizosaccharomyces pombe

To understand the lifespan of higher organisms, including humans, it is important to understand lifespan at the cellular level as a prerequisite. So, fission yeast is a good model organism for the study of lifespan. To identify the novel factors involved in longevity, we are conducting a large-scale screening of long-lived mutant strains that extend chronological lifespan (cell survival in the stationary phase) using fission yeast. One of the newly acquired long-lived mutant strains (No.98 mutant) was selected for analysis and found that the long-lived phenotype was due to a missense mutation (92Phe → Ile) in the plb1+ gene. plb1+ gene in fission yeast is a nonessential gene encoding a homolog of phospholipase B, but its functions under normal growth conditions, as well as phospholipase B activity, remain unresolved. Our analysis of the No.98 mutant revealed that the plb1 mutation reduces the integrity of the cellular membrane and cell wall and activates Sty1 via phosphorylation.

ecl family genes: Factors linking starvation and lifespan extension in Schizosaccharomyces pombe

In the fission yeast Schizosaccharomyces pombe, the duration of survival in the stationary phase, termed the chronological lifespan (CLS), is affected by various environmental factors and the corresponding gene activities. The ecl family genes were identified in the genomic region encoding non-coding RNA as positive regulators of CLS in S. pombe, and subsequently shown to encode relatively short proteins. Several studies revealed that ecl family genes respond to various nutritional starvation conditions via different mechanisms, and they are additionally involved in stress resistance, autophagy, sexual differentiation, and cell cycle control. Recent studies reported that Ecl family proteins strongly suppress target of rapamycin complex 1, which is a conserved eukaryotic nutrient-sensing kinase complex that also regulates longevity in a variety of organisms. In this review, we introduce the regulatory mechanisms of Ecl family proteins and discuss their emerging findings.

Characterization of hexose transporter genes in the views of the chronological life span and glucose uptake in fission yeast

Fission yeast, Schizosaccharomyces pombe, possesses eight hexose transporters, Ght1~8. In order to clarify the role of each hexose transporter on glucose uptake, a glucose uptake assay system was established and the actual glucose uptake activity of each hexose transporter-deletion mutant was measured. Under normal growth condition containing 2% glucose, ∆ght5 and ∆ght2 mutants showed large and small decrease in glucose uptake activity, respectively. On the other hand, the other deletion mutants did not show any decrease in glucose uptake activity indicating that, in the presence of Ght5 and Ght2, the other hexose transporters do not play a significant role in glucose uptake. To understand the relevance between glucose uptake and lifespan regulation, we measured the chronological lifespan of each hexose transporter deletion mutant, and found that only ∆ght5 mutant showed a significant lifespan extension. Based on these results we showed that Ght5 is mainly involved in the glucose uptake in Schizosaccharomyces pombe, and suggested that the ∆ght5 mutant has prolonged lifespan due to physiological changes similar to calorie restriction.

Sporulation: A response to starvation in the fission yeast Schizosaccharomyces pombe

The fission yeast Schizosaccharomyces pombe employs two main strategies to adapt to the environment and survive when starved for nutrients. The strategies employ sporulation via sexual differentiation and extension of the chronological lifespan. When a cell is exposed to nutrient starvation in the presence of a cell of the opposite sex, the cells undergo fusion through conjugation and sporulation through meiosis. S. pombe spores are highly resistant to diverse stresses and may survive for a very long time. In this minireview, among the various sexual differentiation processes induced by starvation, we focused on and summarized the findings of the molecular mechanisms of spore formation in fission yeast. Furthermore, comparative measurements of the chronological lifespan of stationary phase cells and G0 cells and the survival period of spore cells revealed that the spore cells survived for a long period, indicating the presence of an effective mechanism for survival. Currently, many molecules involved in sporulation and their functions are being discovered; however, our understanding of these is not complete. Further understanding of spores may not only deepen our comprehension of sexual differentiation but may also provide hints for sustaining life.

Tschimganine has different targets for chronological lifespan extension and growth inhibition in fission yeast

Tschimganine inhibits growth and extends the chronological lifespan in Schizosaccharomyces pombe. We synthesized a Tschimganine analog, Mochimganine, which extends the lifespan similar to Tschimganine but exhibits a significantly weaker growth inhibition effect. Based on the comparative analysis of these compounds, we propose that Tschimganine has at least 2 targets: one extends the lifespan and the other inhibits growth.

Response to leucine in Schizosaccharomyces pombe (fission yeast)

Leucine (Leu) is a branched-chain, essential amino acid in animals, including humans. Fungi, including the fission yeast Schizosaccharomyces pombe, can biosynthesize Leu, but deletion of any of the genes in this biosynthesis leads to Leu auxotrophy. In this yeast, although a mutation in the Leu biosynthetic pathway, leu1-32, is clearly inconvenient for this species, it has increased its usefulness as a model organism in laboratories worldwide. Leu auxotrophy produces intracellular responses and phenotypes different from those of the prototrophic strains, depending on the growing environment, which necessitates a certain degree of caution in the analysis and interpretation of the experimental results. Under amino acid starvation, the amino acid-auxotrophic yeast induces cellular responses, which are conserved in higher organisms without the ability of synthesizing amino acids. This mini-review focuses on the roles of Leu in S. pombe and discusses biosynthetic pathways, contribution to experimental convenience using a plasmid specific for Leu auxotrophic yeast, signaling pathways, and phenotypes caused by Leu starvation. An accurate understanding of the intracellular responses brought about by Leu auxotrophy can contribute to research in various fields using this model organism and to the understanding of intracellular responses in higher organisms that cannot synthesize Leu.

Identification of ksg1 mutation showing long-lived phenotype in fission yeast

Fission yeast is a good model organism for the study of lifespan. To elucidate the mechanism, we screened for long-lived mutants. We found a nonsense mutation in the ksg1⁺ gene, which encodes an ortholog of mammalian PDK1 (phosphoinositide-dependent protein kinase). The mutation was in the PH domain of Ksg1 and caused defect in membrane localization and protein stability. Analysis of the ksg1 mutant revealed that the reduced amounts and/or activity of the Ksg1 protein are responsible for the increased lifespan. Ksg1 is essential for growth and known to phosphorylate multiple substrates, but the substrate responsible for the long-lived phenotype of ksg1 mutation is not yet known. Genetic analysis showed that deletion of pck2 suppressed the long-lived phenotype of ksg1 mutant, suggesting that Pck2 might be involved in the lifespan extension caused by ksg1 mutation.

Identification of sur2 mutation affecting the lifespan of fission yeast

Yeast is a suitable model system to analyze the mechanism of lifespan. In this study, to identify novel factors involved in chronological lifespan, we isolated a mutant with a long chronological lifespan and found a missense mutation in the sur2+ gene, which encodes a homolog of Saccharomyces cerevisiae sphingolipid C4-hydroxylase in fission yeast. Characterization of the mutant revealed that loss of sur2 function resulted in an extended chronological lifespan. The effect of caloric restriction, a well-known signal for extending lifespan, is thought to be dependent on the sur2+ gene.

Extension of chronological lifespan in Schizosaccharomyces pombe

There are several examples in the nature wherein the mechanism of longevity control of unicellular organisms is evolutionarily conserved with that of higher multicellular organisms. The present microreview focuses on aging and longevity studies, particularly on chronological lifespan (CLS) concerning the unicellular eukaryotic fission yeast Schizosaccharomyces pombe. In S. pombe, >30 compounds, 8 types of nutrient restriction, and >80 genes that extend CLS have been reported. Several CLS control mechanisms are known to be involved in nutritional response, energy utilization, stress responses, translation, autophagy, and sexual differentiation. In unicellular organisms, the control of CLS is directly linked to the mechanism by which cells are maintained in limited‐resource environments, and their genetic information is left to posterity. We believe that this important mechanism may have been preserved as a lifespan control mechanism for higher organisms.

Genes affecting the extension of chronological lifespan in Schizosaccharomyces pombe (fission yeast)

So far, more than 70 genes involved in the chronological lifespan (CLS) of Schizosaccharomyces pombe (fission yeast) have been reported. In this mini‐review, we arrange and summarize these genes based on the reported genetic interactions between them and the physical interactions between their products. We describe the signal transduction pathways that affect CLS in S. pombe: target of rapamycin complex 1, cAMP‐dependent protein kinase, Sty1, and Pmk1 pathways have important functions in the regulation of CLS extension. Furthermore, the Php transcription complex, Ecl1 family proteins, cyclin Clg1, and the cyclin‐dependent kinase Pef1 are important for the regulation of CLS extension in S. pombe. Most of the known genes involved in CLS extension are related to these pathways and genes. In this review, we focus on the individual genes regulating CLS extension in S. pombe and discuss the interactions among them.

gas1 mutation extends chronological lifespan via Pmk1 and Sty1 MAPKs in Schizosaccharomyces pombe

In the longevity research by using yeasts, chronological lifespan is defined as the survival time after entry into stationary phase. Previously, screening for long lived mutants of Schizosaccharomyces pombe was performed to identify the novel factors involved in longevity. From this screening, one long lived mutant called as No.36 was obtained. In this study, we identified the mutation caused in gas1⁺, which encodes glucanosyltransferase (gas1-287 mutation) is responsible for the longevity of No.36 mutant. Through the analysis of this mutant, we found that cell wall perturbing agent micafungin also extends chronological lifespan in fission yeast. This lifespan extension depended on both Pmk1 and Sty1 MAP kinases, and longevity caused by the gas1-287 mutation also depended on these kinases. In summary, we propose that the gas1-287 mutation causes longevity as the similar mechanism as cell wall stress depending on Pmk1 and Sty1 MAPK pathways.