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

The macroscopic limit to synchronization of cellular clocks in single cells of Neurospora crassa

We determined the macroscopic limit for phase synchronization of cellular clocks in an artificial tissue created by a “big chamber” microfluidic device to be about 150,000 cells or less. The dimensions of the microfluidic chamber allowed us to calculate an upper limit on the radius of a hypothesized quorum sensing signal molecule of 13.05 nm using a diffusion approximation for signal travel within the device. The use of a second microwell microfluidic device allowed the refinement of the macroscopic limit to a cell density of 2166 cells per fixed area of the device for phase synchronization. The measurement of averages over single cell trajectories in the microwell device supported a deterministic quorum sensing model identified by ensemble methods for clock phase synchronization. A strong inference framework was used to test the communication mechanism in phase synchronization of quorum sensing versus cell-to-cell contact, suggesting support for quorum sensing. Further evidence came from showing phase synchronization was density-dependent.

Wild Isolates of Neurospora crassa Reveal Three Conidiophore Architectural Phenotypes

The vegetative life cycle in the model filamentous fungus, Neurospora crassa, relies on the development of conidiophores to produce new spores. Environmental, temporal, and genetic components of conidiophore development have been well characterized; however, little is known about their morphological variation. We explored conidiophore architectural variation in a natural population using a wild population collection of 21 strains from Louisiana, United States of America (USA). Our work reveals three novel architectural phenotypes, Wild Type, Bulky, and Wrap, and shows their maintenance throughout the duration of conidiophore development. Furthermore, we present a novel image-classifier using a convolutional neural network specifically developed to assign conidiophore architectural phenotypes in a high-throughput manner. To estimate an inheritance model for this discrete complex trait, crosses between strains of each phenotype were conducted, and conidiophores of subsequent progeny were characterized using the trained classifier. Our model suggests that conidiophore architecture is controlled by at least two genes and has a heritability of 0.23. Additionally, we quantified the number of conidia produced by each conidiophore type and their dispersion distance, suggesting that conidiophore architectural phenotype may impact N. crassa colonization capacity.

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

Using an automated cell counting technique developed previously (Case et al., Ecology and Evolution 2014; 4: 3494), we explore the lifespan effects of lac‐1, a ceramide synthase gene paralogous to lag‐1 in Neurospora crassa in conjunction with the band bd (ras‐1) gene. We find that the replicative lifespan of a lac‐1^KObd double 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 including lac‐1^KO. This short replicative lifespan phenotype is contrasted with a very long estimated chronological lifespan for lac‐1^KObd double mutants from 247 to 462 days based on our regression analyses on log viability, and for the single mutant lac‐1^KO, 161 days. Both of these estimated lifespans are much higher than that of previously studied WT and bd single mutant strains. In a lac‐1 rescue and induction experiment, the expression of lac‐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 control bd conidia 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 stressed N. crassa cells. To test this hypothesis of balancing selection on phytoceramide levels, we examine the viability of WT, lag‐1^KObd, and lac‐1^KObd strains 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 the lag‐1^KObd mutant, but not in the lac‐1^KObd mutant. We conclude that phytoceramide production is responsible for the previously reported longevity effects in the lag‐1^KObd mutant, but a different ceramide may be responsible for the longevity effect observed in the lac‐1^KObd mutant.