Using animal data to improve prediction of human decompression risk following air-saturation dives.

To plan for any future rescue of personnel in a disabled and pressurized submarine, the US Navy needs a method for predicting risk of decompression sickness under possible scenarios for crew recovery. Such scenarios include direct ascent from compressed air exposures with risks too high for ethical human experiments. Animal data, however, with their extensive range of exposure pressures and incidence of decompression sickness, could improve prediction of high-risk human exposures. Hill equation dose-response models were fit, by using maximum likelihood, to 898 air-saturation, direct-ascent dives from humans, pigs, and rats, both individually and combined. Combining the species allowed estimation of one, more precise Hill equation exponent (steepness parameter), thus increasing the precision associated with human risk predictions. These predictions agreed more closely with the observed data at 2 ATA, compared with a current, more general, US Navy model, although the confidence limits of both models overlapped those of the data. However, the greatest benefit of adding animal data was observed after removal of the highest risk human exposures, requiring the models to extrapolate.     

Staphylococcus aureus lactate‐ and malate‐quinone oxidoreductases contribute to nitric oxide resistance and virulence

Staphylococcus aureus is a Gram‐positive pathogen that resists many facets of innate immunity including nitric oxide (NO·). Staphylococcus aureus NO‐resistance stems from its ability to evoke a metabolic state that circumvents the negative effects of reactive nitrogen species. The combination of l ‐lactate and peptides promotes S. aureus growth at moderate NO‐levels, however, neither nutrient alone suffices. Here, we investigate the staphylococcal malate‐quinone and l ‐lactate‐quinone oxidoreductases (Mqo and Lqo), both of which are critical during NO‐stress for the combined utilization of peptides and l ‐lactate. We address the specific contributions of Lqo‐mediated l ‐lactate utilization and Mqo‐dependent amino acid consumption during NO‐stress. We show that Lqo conversion of l ‐lactate to pyruvate is required for the formation of ATP, an essential energy source for peptide utilization. Thus, both Lqo and Mqo are essential for growth under these conditions making them attractive candidates for targeted therapeutics. Accordingly, we exploited a modelled Mqo/Lqo structure to define the catalytic and substrate‐binding residues.We also compare the S. aureus Mqo/Lqo enzymes to their close relatives throughout the staphylococci and explore the substrate specificities of each enzyme. This study provides the initial characterization of the mechanism of action and the immunometabolic roles for a newly defined staphylococcal enzyme family.     

Correlation between the number of adult male Pectinophora gossypiella (Saund.) (Lep., Gelechidae) catches on pheromone traps and the rate of infestation in fruiting bodies of cotton plants by young larvae in three regions of central Greece

In order to evaluate the influence of the number of catches in pheromone-baited traps on the percentage of larval infestation, six delta traps equipped with sex attractant were placed in each of three regions in Central Greece (Farkadona, Farsala, Almyros) in cotton fields from 20 June until 30 September 1995. The collection of fruiting bodies took place weekly and the counting of adults in the traps was carried out each day. The population fluctuation in all three regions was similar with their peak during the first weeks of August. In Farkadona the infestation level was low (1% at the first sampling of August) with a maximum of 9% in the last sampling of September. In Farsala and Almyros, the infestation level was already high (10% and above) in early August. There was a significant positive linear correlation between the number of moth catches and the infestation percentage from first- and second-stage larvae on the first (R = 0694) and second (R = 0.7399) boll-feeding generations.     

Charge-to-Alanine Mutagenesis of the Adeno-Associated Virus Type 2 Rep78/68 Proteins Yields Temperature-Sensitive and Magnesium-Dependent Variants

The adeno-associated virus type 2 (AAV) replication (Rep) proteins Rep78 and 68 (Rep78/68) exhibit a number of biochemical activities required for AAV replication, including specific binding to a 22-bp region of the terminal repeat, site-specific endonuclease activity, and helicase activity. Individual and clusters of charged amino acids were converted to alanines in an effort to generate a collection of conditionally defective Rep78/68 proteins. Rep78 variants were expressed in human 293 cells and analyzed for their ability to mediate replication of recombinant AAV vectors at various temperatures. The biochemical activities of Rep variants were further characterized in vitro by using Rep68 His-tagged proteins purified from bacteria. The results of these analyses identified a temperature-sensitive (ts) Rep protein (D40,42,44A-78) that exhibited a delayed replication phenotype at 32 degrees C, which exceeded wild-type activity by 48 h. Replication activity was reduced by more than threefold at 37 degrees C and was undetectable at 39 degrees C. Stability of the Rep78 protein paralleled replication levels at each temperature, further supporting a ts phenotype. Replication differences resulted in a 3-log-unit difference in virus yields between the permissive and nonpermissive temperatures (2.2 x 10(6) and 3 x 10(3), respectively), demonstrating that this is a relatively tight mutant. In addition to the ts Rep mutant, we identified a nonconditional mutant with a reduced ability to support viral replication in vivo. Additional characterization of this mutant demonstrated an Mg(2+)-dependent phenotype that was specific to Rep endonuclease activity and did not affect helicase activity. The two mutants described here are unique, in that Rep ts mutants have not previously been described and the D412A Rep mutant represents the first mutant in which the helicase and endonuclease functions can be distinguished biochemically. Further understanding of these mutants should facilitate our understanding of AAV replication and integration, as well as provide novel strategies for production of viral vectors.     

Stem cells in the embryonic cerebral cortex: Their role in histogenesis and patterning

The cytoarchitectural simplicity of the cerebral cortex makes it an attractive system to study central nervous system (CNS) histogenesis—the process whereby diverse cells are generated in the right numbers at the appropriate place and time. Recently, multipotent stem cells have been implicated in this process, as progenitor cells for diverse types of cortical neurons and glia. Continuous analysis of stem cell clone development reveals stereotyped division patterns within their lineage trees, highly reminiscent of neural lineage trees in arthropods and Caenorhabditis elegans. Given that these division patterns play a critical part in generating diverse neural types in invertebrates, we speculate that they play a similar role in the cortex. Because stereotyped lineage trees can be observed from cells growing at clonal density, cell-intrinsic factors are likely to have a key role in stem cell behavior. Cortical stem cells also respond to environmental signals to alter the types of cells they generate, providing the means for feedback regulation on the germinal zone. Evidence is accumulating that cortical stem cells, influenced by intrinsic programs and environmental signals, actually change with development—for example, by reducing the number and types of neurons they produce. Age-related changes in the stem cell population may have a critical role in orchestrating development; whether these cells truly self-renew is a point of discussion. In summary, we propose that cortical stem cells are the focus of regulatory mechanisms central to the development of the cortical cytoarchitecture. © 1998 John Wiley & Sons, Inc. J Neurobiol 36: 162–174, 1998     

Host age and fitness-related traits in a koinobiont aphid parasitoid

Abstract.  1. Trade-offs play a key role in species evolution and should be found in host–parasitoid interactions where the host quality may differ between host age categories.
2. The braconid wasp, Aphidius ervi , is a solitary endoparasitoid that allows its aphid hosts to continue to feed and grow after parasitisation. The hypotheses that host age influences their quality and that female parasitoids exploit their hosts based on that quality were tested under laboratory conditions using no-choice tests.
3.  Aphidius ervi females accepted the aphid Myzus persicae for oviposition and their progeny developed successfully in all host ages. The fitness-related traits of parasitoids did not increase linearly with the host age in which they developed. Host quality was found to be optimal at intermediate host ages and the females preferred to parasitise these hosts. The shortest progeny development time and a more female-biased sex ratio were observed in hosts of intermediate age.
4. This study suggests the existence of multiple interactive trade-offs occurring during host–parasitoid interactions according to host age related quality.     

The incredible elastic brain: how neural stem cells expand our minds

Brain development was thought to be largely hardwired and accomplished by birth, and the brain was thought to have essentially no regenerative capacity. The remarkable discovery of adult neurogenesis and neural stem cells (NSCs) existing in the mature CNS changed that, allowing us to think optimistically about CNS repair. These discoveries helped to generate a robust field of neural progenitor cell biology, with relevance to CNS development, pathogenesis, the search for novel neurological therapies, as well as our understanding of how the brain works.     

Chromosomal rearrangement inferred from comparisons of 12 Drosophila genomes

The availability of 12 complete genomes of various species of genus Drosophila provides a unique opportunity to analyze genome-scale chromosomal rearrangements among a group of closely related species. This article reports on the comparison of gene order between these 12 species and on the fixed rearrangement events that disrupt gene order. Three major themes are addressed: the conservation of syntenic blocks across species, the disruption of syntenic blocks (via chromosomal inversion events) and its relationship to the phylogenetic distribution of these species, and the rate of rearrangement events over evolutionary time. Comparison of syntenic blocks across this large genomic data set confirms that genetic elements are largely (95%) localized to the same Muller element across genus Drosophila species and paracentric inversions serve as the dominant mechanism for shuffling the order of genes along a chromosome. Gene-order scrambling between species is in accordance with the estimated evolutionary distances between them and we find it to approximate a linear process over time (linear to exponential with alternate divergence time estimates). We find the distribution of synteny segment sizes to be biased by a large number of small segments with comparatively fewer large segments. Our results provide estimated chromosomal evolution rates across this set of species on the basis of whole-genome synteny analysis, which are found to be higher than those previously reported. Identification of conserved syntenic blocks across these genomes suggests a large number of conserved blocks with varying levels of embryonic expression correlation in Drosophila melanogaster. On the other hand, an analysis of the disruption of syntenic blocks between species allowed the identification of fixed inversion breakpoints and estimates of breakpoint reuse and lineage-specific breakpoint event segregation.     

A comparison of two methods for assessing critical flicker fusion frequency in hens

This paper compared two general methods for assessing critical fusion frequency in hens (gallus gallus domesticus). The first method was a conditional discrimination procedure with the stimuli presented successively. The second was a two-alternative forced-choice procedure with the stimuli presented simultaneously. It was found that both methods of stimulus presentation gave comparable results suggesting that either method is useful when investigating psychophysics in animals. The results also show that hens’ critical fusion frequency is considerably higher than that of humans which may account for hens’ inability to recognise images presented on standard computer or television monitors.