Project description:Studies using yeast have advanced our understanding of both replicative and chronological aging, leading to the discovery of longevity genes that have homologues in higher eukaryotes. Chronological lifespan in yeast is conventionally defined as the lifespan of a non-dividing cell. To date, this parameter has only been estimated under calorically restricted (CR) conditions, mimicked by starvation. Since post-mitotic cells in higher eukaryotes are rarely calorically-restricted, we sought to develop an alternative experimental system where non-dividing yeast would age chronologically, in the presence of excess nutrients. We report here on a system wherein alginate-encapsulated yeast are packed in a pH- and temperature-controlled bioreactor, then continuously fed non-limiting substrate for extended periods of time. We present demographic, physiological and genomic evidence indicating that after ~120 hrs, immobilized cells cease dividing, remain metabolically very active and retain >95% viability for periods of 17 days. Over the same time interval, starved planktonic cells, cultured using the same media, and also controlled for temperature and pH, retained < 1 % viability in both aerobic and anaerobic cultures,. Unlike planktonic yeast, continuously-fed immobilized cells hyper-accumulate glycogen. FACS analysis of SYTOX green-stained yeast confirms that immobilized cells completely arrest within 5 days of culture, and unlike starving planktonic cells, remain free thereafter of replicative stress and are non-apoptotic. This unusual state is supported by a global gene expression profile that is stable over time, repeatable across replicate experiments, and altogether distinct from planktonic cells cultured in the presence and absence of limiting nutrients. DNA expression profiling, performed here for the very first time on immobilized cells, reveals that glycolytic genes and their trans-acting regulatory elements are upregulated, as are genes involved in remodeling the cell wall and resisting stress; by contrast, many genes that promote cell cycle progression and carry out oxidative metabolism are repressed. Stress resistance transcription factor MSN4 and its upstream effector RIM15 are conspicuously upregulated in the immobilized state, suggesting that nutrient-sensing pathways may play a role in cell viability and longevity when yeast are immobilized and placed in prolonged culture under calorically-unrestricted conditions. The cell cycle arrest in the immobilized state is mediated by RIM 15. Over the time-course of our experiments, well-fed, non-diving immobilized cells do not appear to age. Keywords: comparison of growth states and a time course of immobilized cells Nine growth conditions or time points with two to four replicates each

Project description:The chronological lifespan (CLS) of Saccharomyces cerevisiae is defined as the number days that non-dividing cells remain viable, typically in stationary phase cultures or in water. CLS is extended by restricting glucose in the starting cultures, and is considered a form of caloric restriction (CR). Through a previous genetic screen our lab determined that deleting components of the de novo purine biosynthesis pathway also significantly increased CLS. Significant similarities in gene expression profiles between calorie restricted WT cells and a non-restricted ade4M-bM-^HM-^F mutant suggested the possibility of common gene expression biomarkers of all chronologically long lived cells that could also provide insights into general mechanisms of lifespan extension. We have identified additional growth conditions that extend CLS of WT cells, including supplementation of the media with isonicotinamide (INAM), a known sirtuin activator, or by supplementation with a concentrate collected from the expired media of a calorie restricted yeast culture, presumably due to an as yet unidentified longevity factor. Using these varied methods to extend CLS, we compared gene expression profiles in the aging cells (at day 8) to identify functionally relevant biomarkers of longevity. Nineteen genes were differentially regulated in all 4 of the long-lived populations relative to wild type. Of these 19 genes, viable haploid deletion mutants were available for 16 of them, and 12 were found to have a significant impact on CLS. Duplicate cultures were grown to saturation in SC media cultures, aged, and then harvested on day 8. The deletion mutant ade4M-bM-^HM-^F as well as WT cells treated with 25 mM isonicotinamide, calorie restricted (0.5% glucose), or treated with expired media concentrate from previously calorie restricted cultures. These 4 conditions were then compared to a wild-type (WT) strain. Total RNA was isolated and used for microarray hybridizations onto Affymetrix Yeast 2.0 Gene arrrays.

Project description:The present study aims to explore the role of Rim15 in both physiology and genome wide expression in S. cerevisiae under severe caloric restriction. Non-growing but metabolically active cultures of S. cerevisiae are of major interest for application in industry and as model systems for aging in higher eukaryotes. Using retentostat cultivations, almost non-growing but metabolic active cultures can be obtained resulting from the severe caloric restriction, yet not starvation, yeast experiences. Rim15 plays an important role in several nutrient sensing pathways and is involved in activating stress response and glycogen accumulation upon nutrient shortage. To investigate the role of Rim15 in the extreme robustness and glycogen accumulation of anaerobic retentostat cultures, a rim15 deletion strain is compared with its parental strain under anaerobic calorie restriction on both physiology and transcriptome. Rim15 is described as essential for G0 entry and glycogen accumulation in yeast during diauxic shift and stationary phase. Anaerobic retentostat cultures display many stationary phase characteristics, including increased expression levels of Rim15 target genes, suggesting an important role for Rim15 under these conditions. Comparing a rim15 deletion strain and its parental strain revealed both on transcriptome level and physiology indeed a major role in the acquired robustness, glycogen accumulation, but also maintenance of viability and cell cycle arrest. The severe caloric restriction, but not starving, conditions applied together with a thorough physiological and transcriptome analysis of the cultures shows that Rim15 is essential in fine-tuning cell cycle progression with glucose availability under extreme growth-limiting conditions. To investigate the impact of rim15 deletion under severe calorie restricted conditions, transcriptome of a S. cerevisiae rim15 deletion mutant was monitored during anaerobic retentostat cultivation. Five time points were used, one in the starting point of the retentostat (T0 = chemostat) and four during the course of the retentostat (time points 2, 9, 16 and 20 days). Culture triplicates were performed for T0 in chemostat, while two independent cultures were run for retentostat.

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Saccharomyces cerevisiae BY4741

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