Extension of chronological lifespan in Schizosaccharomyces pombe

A novel transcription factor Sdr1 involving sulfur depletion response in fission yeast

In the fission yeast Schizosaccharomyces pombe, the response to sulfur depletion has been less studied compared to the response to nitrogen depletion. Our study reveals that the fission yeast gene, SPCC417.09c, plays a significant role in the sulfur depletion response. This gene encodes a protein with a Zn2Cys6 fungal-type DNA-binding domain and a transcription factor domain, and we have named it sdr1+ (sulfur depletion response 1). Interestingly, while sulfur depletion typically induces autophagy akin to nitrogen depletion, we found that autophagy was not induced under sulfur depletion in the absence of sdr1+. This suggests that sdr1+ is necessary for the induction of autophagy under conditions of sulfur depletion. Although sdr1+ is not essential for the growth of fission yeast, its overexpression, driven by the nmt1 promoter, inhibits growth. This implies that Sdr1 may possess cell growth-inhibitory capabilities. In addition, our analysis of Δsdr1 cells revealed that sdr1+ also plays a role in regulating the expression of genes associated with the phosphate depletion response. In conclusion, our study introduces Sdr1 as a novel transcription factor that contributes to an appropriate cellular nutrient starvation response. It does so by inhibiting inappropriate cell growth and inducing autophagy in response to sulfur depletion.

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.

Structure-based engineering of Tor complexes reveals that two types of yeast TORC1 produce distinct phenotypes

Certain proteins assemble into diverse complex states, each having a distinct and unique function in the cell. Target of rapamycin (Tor) complex 1 (TORC1) plays a central role in signalling pathways that allow cells to respond to the environment, including nutritional status signalling. TORC1 is widely recognised for its association with various diseases. The budding yeast Saccharomyces cerevisiae has two types of TORC1, Tor1-containing TORC1 and Tor2-containing TORC1, which comprise different constituent proteins but are considered to have the same function. Here, we computationally modelled the relevant complex structures and then, based on the structures, rationally engineered a Tor2 mutant that could form Tor complex 2 (TORC2) but not TORC1, resulting in a redesign of the complex states. Functional analysis of the Tor2 mutant revealed that the two types of TORC1 induce different phenotypes, with changes observed in rapamycin, caffeine and pH dependencies of cell growth, as well as in replicative and chronological lifespan. These findings uncovered by a general approach with huge potential - model structure-based engineering - are expected to provide further insights into various fields such as molecular evolution and lifespan.

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.

The ecl family gene ecl3+ is induced by phosphate starvation and contributes to sexual differentiation in fission yeast

In Schizosaccharomyces pombe, ecl family genes are induced by several signals, such as starvation of various nutrients, including sulfur, amino acids and Mg2+, and environmental stress, including heat or oxidative stress. These genes mediate appropriate cellular responses and contribute to the maintenance of cell viability and induction of sexual differentiation. Although this yeast has three ecl family genes with overlapping functions, any environmental conditions that induce ecl3+ remain unidentified. We demonstrate that ecl3+ is induced by phosphate starvation, similar to its chromosomally neighboring genes, pho1+ and pho84+, which respectively encode an extracellular acid phosphatase and an inorganic phosphate transporter. ecl3+ expression was induced by the transcription factor Pho7 and affected by the cyclin-dependent kinase (CDK)-activating kinase Csk1. Phosphate starvation induced G1 arrest and sexual differentiation via ecl family genes. Biochemical analyses suggested that this G1 arrest was mediated by the stabilization of the CDK inhibitor Rum1, which was dependent on ecl family genes. This study shows that ecl family genes are required for appropriate responses to phosphate starvation and provides novel insights into the diversity and similarity of starvation responses.

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.

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.