A modelling approach to quantify dynamic crosstalk between the pheromone and the starvation pathway in baker's yeast

Cells must be able to process multiple information in parallel and, moreover, they must also be able to combine this information in order to trigger the appropriate response. This is achieved by wiring signalling pathways such that they can interact with each other, a phenomenon often called crosstalk. In this study, we employ mathematical modelling techniques to analyse dynamic mechanisms and measures of crosstalk. We present a dynamic mathematical model that compiles current knowledge about the wiring of the pheromone pathway and the filamentous growth pathway in yeast. We consider the main dynamic features and the interconnections between the two pathways in order to study dynamic crosstalk between these two pathways in haploid cells. We introduce two new measures of dynamic crosstalk, the intrinsic specificity and the extrinsic specificity. These two measures incorporate the combined signal of several stimuli being present simultaneously and seem to be more stable than previous measures. When both pathways are responsive and stimulated, the model predicts that (a) the filamentous growth pathway amplifies the response of the pheromone pathway, and (b) the pheromone pathway inhibits the response of filamentous growth pathway in terms of mitogen activated protein kinase activity and transcriptional activity, respectively. Among several mechanisms we identified leakage of activated Ste11 as the most influential source of crosstalk. Moreover, we propose new experiments and predict their outcomes in order to test hypotheses about the mechanisms of crosstalk between the two pathways. Studying signals that are transmitted in parallel gives us new insights about how pathways and signals interact in a dynamical way, e.g., whether they amplify, inhibit, delay or accelerate each other

The wetting state of water on a rose petal

The rose petal features surface structures that offer unique wetting properties. A water droplet placed on a rose petal forms a high contact angle but exhibits significant contact angle hysteresis, such that relatively large droplets remain stuck to the surface when it is tilted. Understanding this distinctive ‘parahydrophobic’ wetting behavior can provide insight into the design of highly nonwetting, yet highly adhesive, synthetic surfaces. Surface features of the rose petal are characterized via focused ion beam scanning electron microscopy, which reveals microscale papillae that are partially covered with nanoscale striae. The wetting state of water on a rose petal is directly visualized using confocal microscopy. This experimental evidence confirms the microscale wetting behavior on the papillae, but cannot resolve the wetting behavior on the nanoscale striae. To infer the wetting state on the striae, an energyminimization- based model is developed and the results from the model are compared to the experimental evidence. In combination, the experimental findings and the model results reveal the wetting state of water on the hierarchical surface structure and explain the macroscopic wetting behavior of the rose petal

Low-emissivity impact craters on Venus

An analysis of 144 impact craters on Venus has shown that 11 of these have floors with average emissivities lower than 0.8. The remaining craters have emissivities between 0.8 and 0.9, independent of the specific backscatter cross section of the crater floors. These 144 impact craters were chosen from a possible 164 craters with diameters greater than 30 km as identified by researchers for 89 percent of the surface of Venus. We have only looked at craters below 6053.5 km altitude because a mineralogical change causes high reflectivity/low emissivity above the altitude. We have also excluded all craters with diameters smaller than 30 km because the emissivity footprint at periapsis is 16 x 24 km and becomes larger at the poles

Nuclear fusion and renewable energy forms: Are they compatible?

Nuclear fusion can be considered as a base-load power plant technology: High investment costs and limited operational flexibility require continuous operation. Wind and solar, on the other hand, as the putative main pillars of a future renewable energy system, are intermittent power sources. The resulting variations that occur on many different time scales require at first sight a rather flexible back-up system to balance this stochastic behavior. Fusion would appear not to be well suited for this task. The situation changes, however, if a large-scale renewable energy system is envisaged based on a transnational, or even transcontinental power grid. The present paper discusses a possible European power system in the year 2050 and beyond. A high percentage share of renewable energies and a strong power grid spanning the whole of Europe and involving neighboring countries, in particular those in North Africa, are assumed. The linear programming model URBS is used to describe the power system. The model optimizes the overall system costs and simulates power plant operation with an hourly resolution for one whole year. The geographical resolution is at least at the country level. The renewable technologies are modeled first on a more local level and then summed together at the country or regional level. The results indicate that the smoothing effects of the large-scale power grid transform the intermittent renewable supply, which is then more compatible with base-load power plants such as fusion reactors

Tempo and mode of early gene loss in endosymbiotic bacteria from insects

BACKGROUND: Understanding evolutionary processes that drive genome reduction requires determining the tempo (rate) and the mode (size and types of deletions) of gene losses. In this study, we analysed five endosymbiotic genome sequences of the gamma-proteobacteria (three different Buchnera aphidicola strains, Wigglesworthia glossinidia, Blochmannia floridanus) to test if gene loss could be driven by the selective importance of genes. We used a parsimony method to reconstruct a minimal ancestral genome of insect endosymbionts and quantified gene loss along the branches of the phylogenetic tree. To evaluate the selective or functional importance of genes, we used a parameter that measures the level of adaptive codon bias in E. coli (i.e. codon adaptive index, or CAI), and also estimates of evolutionary rates (Ka) between pairs of orthologs either in free-living bacteria or in pairs of symbionts. RESULTS: Our results demonstrate that genes lost in the early stages of symbiosis were on average less selectively constrained than genes conserved in any of the extant symbiotic strains studied. These results also extend to more recent events of gene losses (i.e. among Buchnera strains) that still tend to concentrate on genes with low adaptive bias in E. coli and high evolutionary rates both in free-living and in symbiotic lineages. In addition, we analyzed the physical organization of gene losses for early steps of symbiosis acquisition under the hypothesis of a common origin of different symbioses. In contrast with previous findings we show that gene losses mostly occurred through loss of rather small blocks and mostly in syntenic regions between at least one of the symbionts and present-day E. coli. CONCLUSION: At both ancient and recent stages of symbiosis evolution, gene loss was at least partially influenced by selection, highly conserved genes being retained more readily than lowly conserved genes: although losses might result from drift due to the bottlenecking of endosymbiontic populations, we demonstrated that purifying selection also acted by retaining genes of greater selective importance

Apollo experiment S-217 IR/radar study of Apollo data

An experiment using Earth based remote sensing radar, infrared eclipse, and color difference data to deduce surface properties not visible in Apollo photography is reported. The Earth based data provided information on the small scale (centimeter sized) blockiness and on the surface chemical composition (titanium and iron contents) of the lunar surface. These deduced surface properties complemented the new Apollo photography, leading to refined geologic interpretations of the lunar surface

Impact craters on Venus: An overview from Magellan observations

Magellan has revealed an ensemble of impact craters on Venus that is unique in many important ways. We have compiled a database describing 842 craters on 89 percent of the planet's surface mapped through orbit 2578 (the craters range in diameter from 1.5 to 280 km). We have studied the distribution, size-frequency, morphology, and geology of these craters both in aggregate and, for some craters, in more detail. We have found the following: (1) the spatial distribution of craters is highly uniform; (2) the size-density distribution of craters with diameters greater than or equal to 35 km is consistent with a 'production' population having a surprisingly young age of about 0.5 Ga (based on the estimated population of Venus-crossing asteroids); (3) the spectrum of crater modification differs greatly from that on other planets--62 percent of all craters are pristine, only 4 percent volcanically embayed, and the remainder affected by tectonism, but none are severely and progressively depleted based on size-density distribution extrapolated from larger craters; (4) large craters have a progression of morphologies generally similar to those on other planets, but small craters are typically irregular or multiple rather than bowl shaped; (5) diffuse radar-bright or -dark features surround some craters, and about 370 similar diffuse 'splotches' with no central crater are observed whose size-density distribution is similar to that of small craters; and (6) other features unique to Venus include radar-bright or -dark parabolic arcs opening westward and extensive outflows originating in crater ejecta

Automated Ensemble Modeling with modelMaGe: Analyzing Feedback Mechanisms in the Sho1 Branch of the HOG Pathway

In systems biology uncertainty about biological processes translates into alternative mathematical model candidates. Here, the goal is to generate, fit and discriminate several candidate models that represent different hypotheses for feedback mechanisms responsible for downregulating the response of the Sho1 branch of the yeast high osmolarity glycerol (HOG) signaling pathway after initial stimulation. Implementing and testing these candidate models by hand is a tedious and error-prone task. Therefore, we automatically generated a set of candidate models of the Sho1 branch with the tool modelMaGe. These candidate models are automatically documented, can readily be simulated and fitted automatically to data. A ranking of the models with respect to parsimonious data representation is provided, enabling discrimination between candidate models and the biological hypotheses underlying them. We conclude that a previously published model fitted spurious effects in the data. Moreover, the discrimination analysis suggests that the reported data does not support the conclusion that a desensitization mechanism leads to the rapid attenuation of Hog1 signaling in the Sho1 branch of the HOG pathway. The data rather supports a model where an integrator feedback shuts down the pathway. This conclusion is also supported by dedicated experiments that can exclusively be predicted by those models including an integrator feedback