The aging biological clock in Neurospora crassa

Abstract

The biological clock affects aging through ras-1 (bd) and lag-1, and these two longevity genes together affect a clock phenotype and the clock oscillator in Neurospora crassa. Using an automated cell-counting technique for measuring conidial longevity, we show that the clock-associated genes lag-1 and ras-1 (bd) are true chronological longevity genes. For example, wild type (WT) has an estimated median life span of 24 days, while the double mutant lag-1, ras-1 (bd) has an estimated median life span of 120 days for macroconidia. We establish the biochemical function of lag-1 by complementing LAG1 and LAC1 in Saccharomyces cerevisiae with lag-1 in N. crassa. Longevity genes can affect the clock as well in that, the double mutant lag-1, ras-1 (bd) can stop the circadian rhythm in asexual reproduction (i.e., banding in race tubes) and lengthen the period of the frequency oscillator to 41 h. In contrast to the ras-1 (bd), lag-1 effects on chronological longevity, we find that this double mutant undergoes replicative senescence (i.e., the loss of replication function with time), unlike WT or the single mutants, lag-1 and ras-1 (bd). These results support the hypothesis that sphingolipid metabolism links aging and the biological clock through a common stress response

lac‐1 and lag‐1 with ras‐1 affect aging and the biological clock in Neurospora crassa

“…Our previous publication revealed that the longevity assurance gene ( lag‐1 ), a gene encoding a ceramide synthase, not only is a longevity gene but also exerts control over the biological clock in the model organism Neurospora crassa (Case et al., 2014). Circadian rhythms and biological clocks play important roles in diverse cellular processes across the tree of life (Bell‐Pederson et al 2005).…”

“…At the organismal level, transcriptomic studies using microarray technologies have shown that nearly twenty‐five percent of the genes in the N. crassa have a circadian response, revealing that the biological clock has evolved as an important mechanism for controlling many biochemical processes (Dong et al., 2008). These same transcriptional studies revealed a transient response in transcription levels of lag‐1 under knockdown of white collar‐1 ( wc‐1) , an important N. crassa clock gene (Case et al., 2014). These findings spurred our interest in studying the longevity and clock effects of lag‐1 knockouts, along with our current study on knockouts of the lag‐1 paralog, longevity assurance cognate‐1 ( lac‐1 ).…”

“…From our recent publication, we found that a lag‐1 knockout combined with a band ( bd) mutation in N. crassa (more recently identified with the mammalian protooncogene ras‐1, Belden et al., 2007) seemed to halt the proper functioning of the clock, as revealed by race tube experiments and 48 hour expression profiling of the frq clock oscillator (Case et al., 2014). However, this is not the first known instance of a gene implicated in lipid metabolism exerting a unique effect on clock function.…”

“…Lifespan can be measured in two ways (Bitterman, Medvedik, & Sinclair, 2003; Case et al., 2014). Replicative lifespan is simply how many serial transfers from one race tube to the next can be carried out.…”

“…Estimates of chronological lifespan can be extracted from measurements of conidial viability (Table 2) (Munkres & Furtek, 1984a). Based on our comparison of the two methods, we find that the automated cell counting method is five times more precise than the plating method in estimating viability (Case et al., 2014). …”