Genetic approaches to aging in budding and fission yeasts: new connections and new opportunities

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.

Factors extending the chronological lifespan of yeast: Ecl1 family genes

Ecl1 family genes are conserved among yeast, in which their overexpression extends chronological lifespan. Ecl1 family genes were first identified in the fission yeast Schizosaccharomyces pombe; at the time, they were considered noncoding RNA owing to their short coding sequence of fewer than 300 base pairs. Schizosaccharomyces pombe carries three Ecl1 family genes, ecl1+, ecl2+ and ecl3+, whereas Saccharomyces cerevisiae has one, ECL1. Their overexpression extends chronological lifespan, increases oxidative stress resistance and induces sexual development in fission yeast. A recent study indicated that Ecl1 family genes play a significant role in responding to environmental zinc or sulfur depletion. In this review, we focus on Ecl1 family genes in fission yeast and describe the relationship between nutritional depletion and cellular output, as the latter depends on Ecl1 family genes. Furthermore, we present the roles and functions of Ecl1 family genes characterized to date.

Inactivation of RAD52 and HDF1 DNA repair genes leads to premature chronological aging and cellular instability

The present study aims to investigate the role of radiation sensitive 52 (RAD52) and high-affinity DNA binding factor 1 (HDF1) DNA repair genes on the life span of budding yeasts during chronological aging. Wild type (wt) and rad52, hdf1, and rad52 hdf1 mutant Saccharomyces cerevisiae strains were used. Chronological aging and survival assays were studied by clonogenic assay and drop test. DNA damage was analyzed by electrophoresis after phenol extraction. Mutant analysis, colony forming units and the index of respiratory competence were studied by growing on dextrose and glycerol plates as a carbon source. Rad52 and rad52 hdf1 mutants showed a gradual decrease in surviving fraction in relation to wt and hdf1 mutant during aging. Genomic DNA was spontaneously more degraded during aging, mainly in rad52 mutants. This strain showed an increased percentage of revertant colonies. Moreover, all mutants showed a decrease in the index of respiratory competence during aging. The inactivation of RAD52 leads to premature chronological aging with an increase in DNA degradation and mutation frequency. In addition, RAD52 and HDF1 contribute to maintain the metabolic state, in a different way, during chronological aging. The results obtained could have important implications in the chronobiology of aging.

The forkhead-like transcription factor (Fhl1p) maintains yeast replicative lifespan by regulating ribonucleotide reductase 1 (RNR1) gene transcription

In eukaryotes, numerous genetic factors contribute to the lifespan including metabolic enzymes, signal transducers, and transcription factors. As previously reported, the forkhead-like transcription factor (FHL1) gene was required for yeast replicative lifespan and cell proliferation. To determine how Fhl1p regulates the lifespan, we performed a DNA microarray analysis of a heterozygous diploid strain deleted for FHL1. We discovered numerous Fhl1p-target genes, which were then screened for lifespan-regulating activity. We identified the ribonucleotide reductase (RNR) 1 gene (RNR1) as a regulator of replicative lifespan. RNR1 encodes a large subunit of the RNR complex, which consists of two large (Rnr1p/Rnr3p) and two small (Rnr2p/Rnr4p) subunits. Heterozygous deletion of FHL1 reduced transcription of RNR1 and RNR3, but not RNR2 and RNR4. Chromatin immunoprecipitation showed that Fhl1p binds to the promoter regions of RNR1 and RNR3. Cells harboring an RNR1 deletion or an rnr1-C428A mutation, which abolishes RNR catalytic activity, exhibited a short lifespan. In contrast, cells with a deletion of the other RNR genes had a normal lifespan. Overexpression of RNR1, but not RNR3, restored the lifespan of the heterozygous FHL1 mutant to the wild-type (WT) level. The Δfhl1/FHL1 mutant conferred a decrease in dNTP levels and an increase in hydroxyurea (HU) sensitivity. These findings reveal that Fhl1p regulates RNR1 gene transcription to maintain dNTP levels, thus modulating longevity by protection against replication stress.

Aging and cell death in the other yeasts, Schizosaccharomyces pombe and Candida albicans

How do cells age and die? For the past 20 years, the budding yeast, Saccharomyces cerevisiae, has been used as a model organism to uncover the genes that regulate lifespan and cell death. More recently, investigators have begun to interrogate the other yeasts, the fission yeast, Schizosaccharomyces pombe, and the human fungal pathogen, Candida albicans, to determine if similar longevity and cell death pathways exist in these organisms. After summarizing the longevity and cell death phenotypes in S. cerevisiae, this mini-review surveys the progress made in the study of both aging and programed cell death (PCD) in the yeast models, with a focus on the biology of S. pombe and C. albicans. Particular emphasis is placed on the similarities and differences between the two types of aging, replicative aging, and chronological aging, and between the three types of cell death, intrinsic apoptosis, autophagic cell death, and regulated necrosis, found in these yeasts. The development of the additional microbial models for aging and PCD in the other yeasts may help further elucidate the mechanisms of longevity and cell death regulation in eukaryotes.

Genome-scale studies of aging: challenges and opportunities

Whole-genome studies involving a phenotype of interest are increasingly prevalent, in part due to a dramatic increase in speed at which many high throughput technologies can be performed coupled to simultaneous decreases in cost. This type of genome-scale methodology has been applied to the phenotype of lifespan, as well as to whole-transcriptome changes during the aging process or in mutants affecting aging. The value of high throughput discovery-based science in this field is clearly evident, but will it yield a true systems-level understanding of the aging process? Here we review some of this work to date, focusing on recent findings and the unanswered puzzles to which they point. In this context, we also discuss recent technological advances and some of the likely future directions that they portend.