Yeast nuclear envelope subdomains with distinct abilities to resist membrane expansion

Little is known about what dictates the round shape of the yeast Saccharomyces cerevisiae nucleus. In spo7Delta mutants, the nucleus is misshapen, exhibiting a single protrusion. The Spo7 protein is part of a phosphatase complex that represses phospholipid biosynthesis. Here, we report that the nuclear protrusion of spo7Delta mutants colocalizes with the nucleolus, whereas the nuclear compartment containing the bulk of the DNA is unaffected. Using strains in which the nucleolus is not intimately associated with the nuclear envelope, we show that the single nuclear protrusion of spo7Delta mutants is not a result of nucleolar expansion, but rather a property of the nuclear membrane. We found that in spo7Delta mutants the peripheral endoplasmic reticulum (ER) membrane was also expanded. Because the nuclear membrane and the ER are contiguous, this finding indicates that in spo7Delta mutants all ER membranes, with the exception of the membrane surrounding the bulk of the DNA, undergo expansion. Our results suggest that the nuclear envelope has distinct domains that differ in their ability to resist membrane expansion in response to increased phospholipid biosynthesis. We further propose that in budding yeast there is a mechanism, or structure, that restricts nuclear membrane expansion around the bulk of the DNA.     

Arabidopsis thaliana,a versatile model system for study of eukaryotic genome-maintenance functions

The genome of the model plant Arabidopsis thaliana encodes many orthologs of human genome-maintenance proteins, and in several important cases plant DNA repair and mutation-antagonism functions resemble their mammalian counterparts more closely than do those of established microbial models. These orthologs, in conjunction with the powerful tools now available for work with Arabidopsis and the practical advantages of its small size and rapid life cycle, now make it an attractive model system for study of eukaryotic DNA repair and mutagenesis. Already, null mutations that inactivate proteins involved in repair of DNA double-strand breaks or in DNA translesion synthesis and are lethal in mice have proved to be tolerated by plants. This review compares in some detail the genome-maintenance activities encoded by plants, mammals and microbes, and describes important Arabidopsis tools and life cycle characteristics. It concludes with selected examples that illustrate Arabidopsis advantages and/or reveal new insights into genome-maintenance functions of general interest.     

Molecular motor function in axonal transport in vivo probed by genetic and computational analysis in Drosophila

Bidirectional axonal transport driven by kinesin and dynein along microtubules is critical to neuronal viability and function. To evaluate axonal transport mechanisms, we developed a high-resolution imaging system to track the movement of amyloid precursor protein (APP) vesicles in Drosophila segmental nerve axons. Computational analyses of a large number of moving vesicles in defined genetic backgrounds with partial reduction or overexpression of motor proteins enabled us to test with high precision existing and new models of motor activity and coordination in vivo. We discovered several previously unknown features of vesicle movement, including a surprising dependence of anterograde APP vesicle movement velocity on the amount of kinesin-1. This finding is largely incompatible with the biophysical properties of kinesin-1 derived from in vitro analyses. Our data also suggest kinesin-1 and cytoplasmic dynein motors assemble in stable mixtures on APP vesicles and their direction and velocity are controlled at least in part by dynein intermediate chain.     

Phenotyping for Abiotic Stress Tolerance in Maize

The ability to quickly develop germplasm having tolerance to several complex polygenic inherited abiotic and biotic stresses combined is critical to the resilience of cropping systems in the face of climate change.Molecular breeding offers the tools to accelerate cereal breeding;however,suitable phenotyping proto-cols are essential to ensure that the much-anticipated benefits of molecular breeding can be realized.To facilitate the full potential of molecular tools,greater emphasis needs to be given to reducing the within-experimental site variability,application of stress and characterization of the environment and appropriate phenotyping tools.Yield is a function of many processes throughout the plantcycle,and thus integrative traits that encompass crop performance over time or organization level(i.e.canopy level) will provide a better alternative to instantaneous measurements which provide only a snapshot of a given plant process.Many new phenotyping tools based on remote sensing are now available including non-destructive measurements of growth-related parameters based on spectral reflectance and infrared thermometry to estimate plant water status.Here we describe key field phenotyping protocols for maize with emphasis on tolerance to drought and low nitrogen.     

Does prey size matter? Novel observations of feeding in the leatherback turtle (Dermochelys coriacea) allow a test of predator–prey size relationships

Optimal foraging models predict that large predators should concentrate on large prey in order to maximize their net gain of energy intake. Here, we show that the largest species of sea turtle, Dermochelys coriacea, does not strictly adhere to this general pattern. Field observations combined with a theoretical model suggest that a 300 kg leatherback turtle would meet its energetic requirements by feeding for 3-4 h a day on 4 g jellyfish, but only if prey were aggregated in high-density patches. Therefore, prey abundance rather than prey size may, in some cases, be the overriding parameter for foraging leatherbacks. This is a classic example where the presence of small prey in the diet of a large marine predator may reflect profitable foraging decisions if the relatively low energy intake per small individual prey is offset by high encounter rates and minimal capture and handling costs. This study provides, to our knowledge, the first quantitative estimates of intake rate for this species.     

Human attitudes towards herpetofauna: The influence of folklore and negative values on the conservation of amphibians and reptiles in Portugal

Background

Human values and folklore of wildlife strongly influence the effectiveness of conservation efforts. These values and folklore may also vary with certain demographic characteristics such as gender, age, or education. Reptiles and amphibians are among the least appreciated of vertebrates and are victims of many negative values and wrong ideas resulting from the direct interpretation of folklore. We try to demonstrate how these values and folklore can affect the way people relate to them and also the possible conservation impacts on these animals.

Methods

A questionnaire survey distributed to 514 people in the district of Évora, Portugal, was used to obtain data regarding the hypothesis that the existence of wrong ideas and negative values contributes to the phenomenon of human-associated persecution of these animals. A structural equation model was specified in order to confirm the hypothesis about the possible relationships between the presence of perceptions and negative values about amphibians and reptiles and persecution and anti-conservation attitudes. Sociodemographic variables were also added.

Results

The results of the model suggest that the presence of folklore and negative values clearly predicts persecution and anti-conservation attitudes towards amphibians and reptiles. Also, the existence of folklore varies sociodemographically, but negative values concerning these animals are widespread in the population.

Conclusions

With the use of structural equation models, this work is a contribution to the study of how certain ideas and values can directly influence human attitudes towards herpetofauna and how they can be a serious conservation issue.     

The importance of sand albedo for the thermal conditions on sea turtle nesting beaches

At Ascension Island and Cyprus, major nesting areas for green turtles ( Chelonia mydas ) in the Atlantic and Mediterranean, respectively, visual inspection shows some beaches are light in colour while others are darker. We objectively measured the albedo of the sand on different beaches, i.e. the percentage of the incident solar radiation that was reflected from the sand surface. At sites where albedo was recorded, we also measured the temperature of the sand at nest depths. At both rookeries, the sand temperature was markedly higher on darker beaches due to greater absorption of the incident solar radiation over the diurnal cycle. Temperature loggers buried at nest depths revealed seasonal changes in temperature on both islands, but showed that the lowest temperatures found on the darker beaches rarely dropped below the highest temperatures on the lighter beaches. Sea turtles exhibit temperature-dependent sex determination. Since sand albedo is a major avenue for the production of a range of incubation temperatures on both islands, it will also have profound implications for hatchling sex ratios. In comparison with both Ascension Island and Cyprus, for samples collected from sea turtle rookeries around the world there was an even greater range in sand albedo values. This suggests that sand albedo, a factor that has previously received little consideration, will have profound implications for nest temperatures, and hence hatchling sex ratios, for other populations and species.     

Variation in reproductive output of marine turtles

Most marine turtle species are non-annual breeders and show variation in both the number of eggs laid per clutch and the number of clutches laid in a season. Large levels of inter-annual variation in the number of nesting females have been well documented in green turtle nesting populations and may be linked to environmental conditions. Other species of marine turtle exhibit less variation in nesting numbers. This inter-specific difference is thought to be linked to trophic status. To examine whether individual reproductive output is more variable in the herbivorous green turtle (Chelonia mydas Linneaeus 1758) than the carnivorous loggerhead (Caretta caretta Linneaeus 1758), we examined the nesting of both species in Cyprus over nine seasons. Green turtles showed slower annual growth rates (0.11 cm year⁻¹ curved carapace length (CCL) and 0.27 cm year⁻¹ curved carapace width (CCW)) than loggerhead turtles (0.36 cm year⁻¹ CCL, 0.51 cm year⁻¹ CCW). CCL was highly correlated to mean clutch size in both green (R²=0.51) and loggerhead turtles (R²=0.61) and maximal clutch size of green turtles (R²=0.58). Larger females did not lay a greater number of clutches or have a shorter remigration interval than smaller females of either species. On average, the size of green turtle clutches increased and that of loggerhead turtles decreased as the season progressed. Individual green turtles, however, produced more eggs per clutch through the season to a maximum in the third or fourth clutch. In loggerhead turtles, clutches 1-4 were very similar in size but the fifth clutch was 38% smaller than the first. No individuals of either species were recorded laying more than five clutches. Green turtles may not be able to achieve their maximum reproductive output with respect to clutch size throughout the season, whereas only loggerhead turtles laying five clutches (n=5) appear to become resource depleted. Green turtles nesting in years when large numbers of nests were recorded laid a greater number of clutches than females nesting in years with lower levels of nesting.     

Continuous plankton records stand the test of time: evaluation of flow rates, clogging and the continuity of the CPR time-series

The Continuous Plankton Recorder (CPR) survey is one of themost extensive biological time-series in existence and has beenin operation over major regions of the North Atlantic since1932. However, there is little information about the volumeof water filtered through each sample, but rather a generalassumption has persisted that each sample represents 3 m³. Datafrom electromagnetic flowmeters, deployed on CPRs between 1995and 1998, was examined. The mean volume filtered through sampleswas 3.11 m³ and the effect of clogging on filtration efficiencieswas not great. Consequently, even when the likely variationsin flow due to clogging are taken into account, previously identifiedlinks between zooplankton abundance and climatic signals remainstrong.     

Simple and rapid preparation of gapped plasmid DNA for incorporation of oligomers containing specific DNA lesions

The cytotoxicity, mutagenicity, and carcinogenicity of DNA base lesions are largely determined by the responses of cellular DNA repair proteins, DNA polymerases, and signaling pathways. Elucidation of these processes is thus of high biochemical interest. Such studies increasingly rely on DNA substrates containing specific lesions at defined locations. Although short synthetic DNA oligomers have frequently proved useful, circular plasmid substrates are preferable for much biochemical work, and essential for in vivo studies. However, the complexity of current approaches for preparing such substrates and limitations inherent in the procedures have posed problems. We present here a simple, highly versatile procedure for preparing gapped duplex plasmids, into which oligomers incorporating specific lesions can easily be inserted. Endonuclease N.BstNBI was used to nick twice the same strand of a pUC19-derived plasmid (pUC19HBDa), at two GAGTCNNNN sequences separated by 22 bases. Removal of the 22-nt oligomer and further purification produced a highly pure gapped plasmid. To illustrate application of this procedure, 22-nt oligonucleotides containing a single uracil residue were ligated into the gapped molecules. The pUC19HB(Da) plasmid can be modified to accept almost any DNA-lesion-containing oligomer. Using this new approach to incorporate specific DNA lesions into popular reporter genes will facilitate in vivo study of cellular responses to DNA damage.