title: lac-1andlag-1withras-1affect aging and the biological clock inNeurospora crassa.
abstract: Using an automated cell counting technique developed previously (Case et al.,Ecology and Evolution2014; 4: 3494), we explore the lifespan effects oflac-1, a ceramide synthase gene paralogous tolag-1inNeurospora crassain conjunction with theband bd(ras-1) gene. We find that the replicative lifespan of alac-1KObddouble mutants is short, about one race tube cycle, and this double mutant lacks a strong ~21-hr clock cycle as shown by race tube and fluorometer analysis of fluorescent strains includinglac-1KO. This short replicative lifespan phenotype is contrasted with a very long estimated chronological lifespan forlac-1KObddouble mutants from 247 to 462 days based on our regression analyses on log viability, and for the single mutantlac-1KO, 161 days. Both of these estimated lifespans are much higher than that of previously studied WT andbdsingle mutant strains. In alac-1rescue and induction experiment, the expression oflac-1+as driven by a quinic acid-dependent promoter actually decreases the median chronological lifespan of cells down to only 7 days, much lower than the 34-day median lifespan found in controlbdconidia also grown on quinic acid media, which we interpret as an effect of balancing selection acting on ceramide levels based on previous findings from the literature. Prior work has shown phytoceramides can act as a signal for apoptosis in stressedN. crassacells. To test this hypothesis of balancing selection on phytoceramide levels, we examine the viability of WT,lag-1KObd, andlac-1KObdstrains following the dual stresses of heat and glycolysis inhibition, along with phytoceramide treatments of different dosages. We find that the phytoceramide dosage-response curve is altered in thelag-1KObdmutant, but not in thelac-1KObdmutant. We conclude that phytoceramide production is responsible for the previously reported longevity effects in thelag-1KObdmutant, but a different ceramide may be responsible for the longevity effect observed in thelac-1KObdmutant.
authors.affiliation: Center for Marine Biotechnology and Biomedicine J. Craig Venter Institute-West Coast Campus University of California San Diego Scripps Institution of Oceanography La Jolla CA USA.
authors.forename: John K
authors.initials: JK
authors.lastname: Brunson
authors.affiliation: College of Agricultural and Environmental Sciences University of Georgia Athens GA USA; Genetics Department University of Georgia Athens GA USA.
authors.forename: James
authors.initials: J
authors.lastname: Griffith
authors.affiliation: Genetics Department University of Georgia Athens GA USA.
authors.forename: Daneisha
authors.initials: D
authors.lastname: Bowles
authors.affiliation: Genetics Department University of Georgia Athens GA USA.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Case
authors.affiliation: Genetics Department University of Georgia Athens GA USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Arnold
keywords: Neurospora crassa; aging; balancing selection; biological clock; ceramide; circadian rhythms; lac‐1; lag‐1