bluuebunny/crossref_metadata_2025 huggingface dataset:
Germination is related to seed mass in grasses (Poaceae) of the eastern Qinghai‐Tibetan Plateau, China
Authors: Wu Gaolin , Du Guozhen
Published: May 2008

Seed germination is a vulnerable stage in the plant life cycle. Many studies have focused on effects of seed mass on seed germination within a single species, but few studies have compared species of a common habitat. Poaceae plants are widely distributed on the Qinghai‐Tibetan Plateau. We investigated how seed mass affect seed germination characters with forty‐seven species of Poaceae typical to the alpine meadows of the eastern Qinghai‐Tibetan plateau. The frequency of seed mass classes for these species produced a log‐normal distribution. The weight of the seeds varied from 0.11 mg to 14.4 mg, and the weight variation nearly reached 103%. There were positive correlations between seed mass and germination index (R=0.331, p<0.05) and between seed mass and germination percentage (R=0.168, p>0.05). The results suggest that seed mass of the Poaceae family on the eastern Qinghai–Tibetan plateau is comparatively log‐normal distributed as consistent with other studies, and the larger‐seed species have faster germination than the smaller‐seed species. Seed mass could be considered as one of the maintenance and construction mechanisms for plant communities in alpine meadows.
Linkage disequilibrium structures in cattle and their application to breed identification testing
Authors: Watanabe T. , Hirano T. , Takano A. , Mizoguchi Y. , Sugimoto Y. , Takasuga A.
Published: May 2008

We examined the extent of linkage disequilibrium (LD) block lengths in four breed populations: Japanese Black, Angus, Hereford and Holstein. Three chromosomal regions in which QTL were previously mapped in Japanese Black populations were scanned with 84 microsatellite markers. The estimated LD lengths in these four purebred populations varied from 535 to 683 kb, which is much shorter than the values reported previously. Our findings suggest that QTL can be mapped in sub‐centimorgan regions in these populations using an LD‐mapping method. We also developed breed identification methods to distinguish Japanese Black from Angus, Hereford, Holstein and F1animals (Japanese Black × Holstein) respectively using the haplotypic frequencies of a pair of markers in the breed populations. After assessing the distributions of posterior probabilities to be Japanese Black, we obtained several pairs of markers that completely distinguished Japanese Black from the other breeds. We also obtained several combinations of six markers that completely distinguished Japanese Black animals from F1animals.
Measuring learning from the TRC pharmacology E‐Learning program
Authors: Franson Kari L. , Dubois Eline A. , De Kam Marieke L. , Cohen Adam F.
Published: May 2008

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• E‐Learning is increasingly used to provide medical education

• Visualizing mechanisms appears to be a handy method for students to learn pharmacology

WHAT THIS STUDY ADDS

• E‐learning tools seem to improve individual grades in pharmacology courses. The statistical information provided by the E‐learning tools gives precise insight into the relationship between effort and learning

AIM

Clinical pharmacology at the Leiden University Medical Centre is primarily taught by the Teaching Resource Centre's (TRC) Pharmacology database. The TRC program contains schematic graphics using a unique icon language, explanation texts and feedback questions to explain pharmacology as it pertains to pathophysiology. Nearly each course of the curriculum has a chapter in the TRC database offered for self‐study. Since using the TRC program is not compulsory, the question remains whether students benefit from using it.

METHODS

We compared the parameters of log‐in attempts and time spent at each topic with students' final exam grades. Instead of looking at the regression of time spent on TRC on grade for one course, we looked at the individual student regression of time spent on TRC for different courses on grades. Spending more time using the TRC being associated with higher grades within an individual is a more powerful result than between students within a course, as better students are likely to spend more time using the TRC.

RESULTS

Students increasingly used the program throughout the curriculum. More importantly, the time spent using the program showed that increased TRC use by an individual student is associated with a (small) increase in grade. As expected for a noncompulsory activity, better students (those with higher than average exam scores) logged in to the TRC more frequently, but poorer students appeared to have a larger benefit.

CONCLUSIONS

An increase in TRC use by an individual student correlates with an increase in course grades.
Non‐morph specific predation of peppered moths (Biston betularia) by bats
Authors: MAJERUS MICHAEL E. N.
Published: May 2008

Abstract1. Industrial melanism in the peppered moth, Biston betularia, is one of the foremost examples of natural selection in action.

2. Differential bird predation was suggested as the main agent for the evolution of melanism in the peppered moth by Tutt in the 1890s, with empirical support being published by Kettlewell in the 1950s.

3. Some recent critiques that have attempted to undermine Kettlewell’s work have lacked objectivity, and have been answered previously.

4. One criticism that has not previously been addressed is that of the role of bat predation in the case.

5. The difficulty of using non‐visual differential predation by bats to explain the increase and decrease in melanism in the peppered moth, correlated as it is to pollution levels, is outlined.

6. Predation experiments, in which moths of thetypicaandcarbonariaforms of the peppered moth were released and observed at night, were used to determine whether bats differentially predate these forms.

7. Results of experiments at three sites showed no significant differences in the level of bat predation of the two forms of peppered moth.
Food limitation in the fungus‐gardening ant, Trachymyrmex septentrionalis
Authors: SEAL JON N. , TSCHINKEL WALTER R.
Published: May 2008

Abstract 1. Most ants are more like plants and marine invertebrates than other insects because the adults are sessile and the immature stages are motile.

2. This paper reported the results from a field experiment that increased food levels on the fungus gardening ant, Trachymyrmex septentrionalis, which has served as a model system for understanding the complexities of these obligate mutualisms.

3. Food supplementation increased the growth of the symbiotic fungus and this led to an increase in the amount of fungal biomass. The amount of fungal biomass was generally more important in determining the amount of ant offspring than colony size.

4. The results indicate that the population is food limited and colonies may compete for relatively rare fungal substrate. However, competition in this species is not obvious.
Contrasting effects of repeated summer drought on soil carbon efflux in hydric and mesic heathland soils
Authors: SOWERBY ALWYN , EMMETT BRIDGET A. , TIETEMA ALBERT , BEIER CLAUS
Published: May 2008

Current predictions of climate change include altered rainfall patterns throughout Europe, continental USA and areas such as the Amazon. The effect of this on soil carbon efflux remains unclear although several modelling studies have highlighted the potential importance of drought for carbon storage. To test the importance of drought, and more importantly repeated drought year‐on‐year, we used automated retractable curtains to exclude rain and produce repeated summer drought in three heathlands at varying moisture conditions. This included a hydric system limited by water‐excess (in the UK) and two mesic systems with seasonal water limitation in Denmark (DK) and the Netherlands (NL). The experimental rainfall reductions were set to reflect single year droughts observed in the last decade with exclusion of rain for 2–3 months of the year resulting in a 20–26% reduction in annual rainfall and 23–38% reduction in mean soil moisture during the drought period. Unexpectedly, sustained reduction in soil moisture over winter (between drought periods) was also observed at all three sites, along with a reduction in the maximum water‐holding capacity attained. Three hypotheses are discussed which may have contributed to this lack of recovery in soil moisture: hydrophobicity of soil organic matter, increased water use by plants and increased cracking of the soil. The responses of soil respiration to this change in soil moisture varied among the sites: decreased rates were observed at the water‐limited NL and DK sites whilst they increased at the UK site. Reduced sensitivity of soil respiration to soil temperature was observed at soil moisture contents above 55% at the UK site and below 20% and 13% at the NL and DK sites, respectively. Soil respiration rates recovered to predrought levels in the NL and DK sites during the winter re‐wetting period that indicates any change in soil C storage due to changes in soil C efflux may be short lived in these mesic systems. In contrast, in the hydric UK site after 2 years of drought treatment, the persistent reduction in soil moisture throughout the year resulted in a year‐round increase in soil respiration flux, a response that accelerated over time to 40% above control levels. These findings suggest that carbon‐rich soils with high organic matter content may act as a significant source of CO2 to the atmosphere following repeated summer drought. Nonrecovery of soil moisture and a persistent increase in soil respiration may be the primary mechanism underlying the reported substantial losses of soil carbon from UK organic soils over the last 20 years. These findings indicate that the water status of an ecosystem will be a critical factor to consider in determining the impact of drought on the soil carbon fluxes and storage.
Diagnostic assessment of European gross primary production
Authors: JUNG MARTIN , VERSTRAETE MICHEL , GOBRON NADINE , REICHSTEIN MARKUS , PAPALE DARIO , BONDEAU ALBERTE , ROBUSTELLI MONICA , PINTY BERNARD
Published: May 2008

We present an approach to estimate gross primary production (GPP) using a remotely sensed biophysical vegetation product (fraction of absorbed photosynthetically active radiation, FAPAR) from the European Commission Joint Research Centre (JRC) in conjunction with GPP estimates from eddy covariance measurement towers in Europe. By analysing the relationship between the cumulative growing season FAPAR and annual GPP by vegetation type, we find that the former can be used to accurately predict the latter. The root mean square error of prediction is of the order of 250 gC m−2 yr−1. The cumulative growing season FAPAR integrates over a number of effects relevant for GPP such as the length of the growing season, the vegetation's response to environmental conditions and the amount of light harvested that is available for photosynthesis. We corroborate the proposed GPP estimate (noted FAPAR‐based productivity assessment+land cover, FPA+LC) on the continental scale with results from the MOD17+radiation‐use efficiency model, an artificial neural network up‐scaling approach (ANN) and the Lund–Potsdam–Jena managed Land biosphere model (LPJmL). The closest agreement of the mean spatial GPP pattern among the four models is between FPA+LC and ANN (R2= 0.74). At least some of the discrepancy between FPA‐LC and the other models result from biases of meteorological forcing fields for MOD17+, ANN and LPJmL. Our analysis further implies that meteorological information is to a large degree redundant for GPP estimation when using the JRC‐FAPAR. A major advantage of the FPA+LC approach presented in this paper lies in its simplicity and that it requires no additional meteorological input driver data that commonly introduce substantial uncertainty. We find that results from different data‐oriented models may be robust enough to evaluate process‐oriented models regarding the mean spatial pattern of GPP, while there is too little consensus among the diagnostic models for such purpose regarding inter‐annual variability.
Variability in 20th century climate change reconstructions and its consequences for predicting geographic responses of California mammals
Authors: PARRA JUAN L. , MONAHAN WILLIAM B.
Published: May 2008

Empirical species distribution models are widely used to predict the effects of climate change on biodiversity distribution but rely on multiple assumptions about the certainty of the locality and climate data. Here, we assess the effect of historical climate data variability when forecasting geographic responses of California mammals to 20th century climate change. We first used two methods to derive gridded climate surfaces from weather station data (ANUSPLIN and PRISM) representing two sampling eras: historic (1900–1940) and current (1980–2005). We then used the two sources of climate data in conjunction with a maximum entropy algorithm (MAXENT) to predict both the historic and current distributions of all major mammal species vouchered historically in California. Results indicate that levels of disagreement between the two climate datasets are considerably greater in the historical era than in the current era. For the bioclimatic variables used in modeling historical mammal distributions, precipitation variables were less concordant than temperature variables. These discrepancies are reflected in the low agreement between historic mammal range predictions and further propagated when the historic models are projected to present day. Nonetheless, some common patterns exist across mammal species and climate estimates. Range stability is the most common prediction between the two eras, followed by expansion and contraction. Jepson ecoregions with relatively high levels of range stability include parts of the Great Central Valley and Sierra Nevada, while other parts of the Central Valley, the Sonoran desert, and Central‐ and Southwestern California yield predictions of range shifts. Historical species distribution modeling can greatly inform studies attempting to describe how species will continue to move geographically in response to future changes in climate. We suggest that alternative estimates of historical climate and their uncertainties are ultimately required in order to provide a quantitative measure of the confidence in predicted changes in distribution.
Modelled effects of precipitation on ecosystem carbon and water dynamics in different climatic zones
Authors: GERTEN DIETER , LUO YIQI , Le MAIRE GUERRIC , PARTON WILLIAM J. , KEOUGH CINDY , WENG ENSHENG , BEIER CLAUS , CIAIS PHILIPPE , CRAMER WOLFGANG , DUKES JEFFREY S. , HANSON PAUL J. , KNAPP ALAN A. K. , LINDER SUNE , NEPSTAD DAN , RUSTAD LINDSEY , SOWERBY ALWYN
Published: May 2008

The ongoing changes in the global climate expose the world's ecosystems not only to increasing CO2concentrations and temperatures but also to altered precipitation (P) regimes. Using four well‐established process‐based ecosystem models (LPJ, DayCent, ORCHIDEE, TECO), we explored effects of potentialPchanges on water limitation and net primary production (NPP) in seven terrestrial ecosystems with distinctive vegetation types in different hydroclimatic zones. We found that NPP responses toPchanges differed not only among sites but also within a year at a given site. The magnitudes of NPP change were basically determined by the degree of ecosystem water limitation, which was quantified here using the ratio between atmospheric transpirational demand and soil water supply. Humid sites and/or periods were least responsive to any change inPas compared with moderately humid or dry sites/periods. We also found that NPP responded more strongly to doubling or halving ofPamount and a seasonal shift inPoccurrence than that to alteredPfrequency and intensity at constant annual amounts. The findings were highly robust across the four models especially in terms of the direction of changes and largely consistent with earlierPmanipulation experiments and modelling results. Overall, this study underscores the widespread importance ofPas a driver of change in ecosystems, although the ultimate response of a particular site will depend on the detailed nature and seasonal timing ofPchange.
Climate change hastens the turnover of stream fish assemblages
Authors: BUISSON LAËTITIA , THUILLER WILFRIED , LEK SOVAN , LIM PUY , GRENOUILLET GAËL
Published: May 2008

Stream fish are expected to be significantly influenced by climate change, as they are ectothermic animals whose dispersal is limited within hydrographic networks. Nonetheless, they are also controlled by other physical factors that may prevent them moving to new thermally suitable sites. Using presence–absence records in 655 sites widespread throughout nine French river units, we predicted the potential future distribution of 30 common stream fish species facing temperature warming and change in precipitation regime. We also assessed the potential impacts on fish assemblages' structure and diversity. Only cold‐water species, whose diversity is very low in French streams, were predicted to experience a strong reduction in the number of suitable sites. In contrast, most cool‐water and warm‐water fish species were projected to colonize many newly suitable sites. Considering that cold headwater streams are the most numerous on the Earth's surface, our results suggested that headwater species would undergo a deleterious effect of climate change, whereas downstream species would expand their range by migrating to sites located in intermediate streams or upstream. As a result, local species richness was forecasted to increase greatly and high turnover rates indicated future fundamental changes in assemblages' structure. Changes in assemblage composition were also positively related to the intensity of warming. Overall, these results (1) stressed the importance of accounting for both climatic and topographic factors when assessing the future distribution of riverine fish species and (2) may be viewed as a first estimation of climate change impacts on European freshwater fish assemblages.
Evidence of occult HCV genotypes in haemophilic individuals with unapparent HCV mixed infections
Authors: PARODI C. , CULASSO A. , ALOISI N. , GARCÍA G. , BASTÓN M. , CORTI M. , BIANCO R. P. , CAMPOS R. , ARES B. R. , BARÉ P.
Published: May 2008

Summary.  Individuals with haemophilia who received non heat‐treated factor concentrates were likely to undergo multiple exposures to the hepatitis C virus (HCV). Therefore, HCV mixed‐genotype infections might be more frequent in these patients than in the general population. Their prevalence is extremely variable in similar groups of patients tested by different assays due to the fact that currently available genotyping techniques are not suitable to detect multiple HCV genotypes in a viral population. As an HCV viral reservoir, the peripheral blood mononuclear cell (PBMC) might harbor viral variants distinct from the genotypes detected in plasma. We investigated the presence of HCV genotypes in a group of chronically infected haemophilic patients in the PBMC compartment using a non‐stimulated cell culture system that allows the detection of the HCV genome in culture supernatants. We compared them to the HCV genotypes found in plasma samples. Cell culture experiments performed with PBMC demonstrated the presence of additional HCV genotypes that were undetected in the corresponding plasma samples with the same genotyping technique. Although mixed infections at HCV genotype level became evident in 5.6% of the patients (16/288), the culture methodology increased the number of HCV infections with multiple genotypes to 62.5% (10/16) (P < 0.0001). Once more, the role of mononuclear cells as HCV viral reservoirs is emphasized. Considering minor strains could influence the outcome of treatment, detection of covert HCV mixed‐genotype infections might be essential for choosing the adequate therapeutic regimen.
The prognostic impact of M‐CSF, CSF‐1 receptor, CD68 and CD3 in prostatic carcinoma
Authors: Richardsen E , Uglehus R D , Due J , Busch C , Busund L‐T R
Published: May 2008

Aims:  Macrophage colony‐stimulating factor (M‐CSF) binds to colony‐stimulating factor‐1 receptor (CSF‐1R) and stimulates proliferation and differentiation of monocytes, macrophages and their bone marrow progenitors. M‐CSF, CSF‐1R, the macrophage marker CD68, and the pan T‐lymphocyte marker CD3 are increased in many human cancers. Their prognostic importance in primary prostatic carcinoma has not been fully delineated. The aim was to compare the expression of M‐CSF, CSF‐1R, CD68 and CD3 in metastatic and non‐metastatic prostatic cancer.

Methods and results:  Digital video analysis of tumour cell areas and tumour stromal areas was performed in 59 cancer specimens: 32 patients with metastases and 27 patients without metastases. Expression of M‐CSF and CSF‐1R was recorded as 0 (negative immunoreactivity), 1 (weak), 2 (moderate) or 3 (strong reactivity). Macrophages (CD68) and T lymphocytes (CD3) were detected as proportions of moderately or strongly immunoreactive cells. Patients with metastatic primary cancers showed higher expression of M‐CSF (P < 0.0001, P = 0.005), CSF‐1R (both P < 0.0001) and CD3 (P = 0.007, P < 0.0001) in both tumour cell areas and tumour stromal areas, compared with the non‐metastatic cancers.

Conclusion:  This study suggests that expression of M‐CSF, CSF‐1R and CD3 is a significant prognostic factor in primary prostatic cancers by predicting the development of metastases.
Density‐dependent predation of weed seeds in maize fields
Authors: Westerman Paula R. , Borza Jaclyn K. , Andjelkovic Jelena , Liebman Matt , Danielson Brent
Published: May 2008

Seed predation can cause substantial losses of newly produced weed seeds and can therefore be important in regulating weed densities. The impact on weed population dynamics is greatest if predation acts in a directly density‐dependent manner.

We investigated the effect of between‐patch variability in seed density on seed removal. For this purpose, artificial weed seed patches were created by broadcasting giant foxtail Setaria faberi, at low (1000 seeds m−2), medium (4500 seeds m−2) and high densities (9500 seeds m−2) over 25 ¥ 25 m areas within three maize fields in August. Changes in giant foxtail seed densities were evaluated 3 weeks and 7 weeks post‐application, using soil surface sampling.

Observations of seed predation rate (seeds seed−1 week−1), using seed cards and exclosure cages, activity–densities of invertebrates using pitfall traps, and population estimates of rodents using Sherman live traps, were conducted to understand and explain the dynamics of seeds on the soil surface.

Three weeks after seed addition, seed predation was strongly and inversely density dependent. After 7 weeks, the net response since the start of the experiment exhibited only a weak inverse density dependence. This means that between 3 weeks and 7 weeks after seed addition, the response had reversed from inverse to almost direct density dependence.

During the August–October period, seeds in maize fields were mainly consumed by invertebrates. The most abundant granivorous invertebrates were crickets Gryllus pennsylvanicus and Allonemobius allardi, and carabid beetles, especially Harpalus pensylvanicus. The insects appeared unable to detect and respond numerically to weed patches, resulting in inversely density‐dependent predation, which favours the persistence of weed patches. The granivorous prairie deer mouse Peromyscus maniculatus bairdi, was present but contributed little to overall seed losses in autumn.

Synthesis and applications. The results of this study indicate that weed densities in maize fields currently are not regulated through directly density‐dependent seed predation, because the time between seed shed and seed movement into soil is too short for invertebrates to respond to and level out spatial differences at the scale of weed patches. However, our results suggest that delaying crop harvest and tillage may provide invertebrate predators with more time to attack weed seeds, and may allow for subsequent predation by vertebrates, which would be directly density‐dependent.
Socioeconomic and psychological variables as risk and protective factors for parental well‐being in families of children with intellectual disabilities
Authors: Olsson M. B. , Hwang C. P.
Published: May 2008

Background  The first aim of the present study was to estimate the extent to which differences in well‐being in parents of children with and without intellectual disability (ID) in Sweden can be accounted for by differences in the presence of the risk factors: (1) child disability; (2) socioeconomic disadvantage; (3) household composition; and (4) parental characteristics.

The second aim was concerned with individual variation in well‐being within the group of parents of children with ID. The aim was to estimate if protective factors such as parental personality characteristics (sense of coherence), perceived positive impact of the child and satisfaction with participation in different arenas of life explained variation in well‐being in mothers and fathers of children with ID over and above that explained by the risk factors.

Method  Parents of children with ID (62 mothers and 49 fathers) and control children (183 mothers and 141 fathers) completed postal surveys on well‐being, socioeconomic situation, health, sense of coherence, satisfaction with participation in different arenas of life and the child's impact on the family.

Results  The results showed that mothers of children with ID had lower levels of well‐being than fathers and control parents, but the presence of a child with ID did not in itself predict poorer maternal well‐being. Rather, differences in economic hardship and self‐rated health were the strongest predictors for well‐being. It was further found that 67.7% of the mothers of children with ID scored within the high well‐being group. The predictive power of the model increased significantly for both fathers and mothers when protective factors were added to the model (42 and 78% explained variance compared with 25% with only risk factors).

Conclusions  Well‐being of parents with a child with ID is dependent upon the interplay of risk and protective factors and research needs to address these variables simultaneously.
Sequence differentiation in regions identified by a genome scan for local adaptation
Authors: WOOD HENRY M. , GRAHAME JOHN W. , HUMPHRAY SEAN , ROGERS JANE , BUTLIN ROGER K.
Published: May 2008

Genome scans using large numbers of randomly selected markers have revealed a small proportion of loci that deviate from neutral expectations and so may mark genomic regions that contribute to local adaptation. Measurements of sequence differentiation and identification of genes in these regions is important but difficult, especially in organisms with limited genetic information available. We have followed up a genome scan in the marine gastropod,Littorina saxatilis, by searching a bacterial artificial chromosome library with differentiated and undifferentiated markers, sequencing four bacterial artificial chromosomes and then analysing sequence variation in population samples for fragments at, and close to the original marker polymorphisms. We show that sequence differentiation follows the patterns expected from the original marker frequencies, that differentiated markers identify independent and highly localized sites and that these sites fall outside coding regions. Two differentiated loci are characterized by insertions of putative transposable elements that appear to have increased in frequency recently and which might influence expression of downstream genes. These results provide strong candidate loci for the study of local adaptation inLittorina. They demonstrate an approach that can be applied to follow up genome scans in other taxa and they show that the genome scan approach can lead rapidly to candidate genes in nonmodel organisms.
Mutation in the rel gene of Sorangium cellulosum affects morphological and physiological differentiation
Authors: Knauber Tina , Doss Sabrina D. , Gerth Klaus , Perlova Olena , Müller Rolf , Treuner‐Lange Anke
Published: May 2008

Interruption of the (p)ppGpp synthetase gene (rel) of Sorangium cellulosum So ce56 resulted in loss of ppGpp accumulation after norvaline treatment during exponential growth phase. The rel mutant failed to produce wild‐type levels of the polyketides chivosazol and etnangien in production media. In wild‐type cells expression of the chivosazol biosynthetic operon can be significantly increased by norvaline or α‐methylglucoside. This induction does not occur in the rel mutant. The rel mutant also lost the capability to form multicellular fruiting bodies under nutrient starvation.
The holin of bacteriophage lambda forms rings with large diameter
Authors: Savva Christos G. , Dewey Jill S. , Deaton John , White Rebecca L. , Struck Douglas K. , Holzenburg Andreas , Young Ry
Published: May 2008

Holins control the length of the infection cycle of tailed phages (the Caudovirales) by oligomerizing to form lethal holes in the cytoplasmic membrane at a time dictated by their primary structure. Nothing is currently known about the physical basis of their oligomerization or the structure of the oligomers formed by any known holin. Here we use electron microscopy and single‐particle analysis to characterize structures formed by the bacteriophage λ holin (S105) in vitro. In non‐ionic or mild zwitterionic detergents, purified S105, but not the lysis‐defective variant S105A52V, forms rings of at least two size classes, the most common having inner and outer diameters of 8.5 and 23 nm respectively, and containing approximately 72 S105 monomers. The height of these rings, 4 nm, closely matches the thickness of the lipid bilayer. The central channel is of unprecedented size for channels formed by integral membrane proteins, consistent with the non‐specific nature of holin‐mediated membrane permeabilization. S105 present in detergent‐solubilized rings and in inverted membrane vesicles showed similar sensitivities to proteolysis and cysteine‐specific modification, suggesting that the rings are representative of the lethal holes formed by S105 to terminate the infection cycle and initiate lysis.
A Sinorhizobium meliloti osmosensory two‐component system required for cyclic glucan export and symbiosis
Authors: Griffitts Joel S. , Carlyon Rebecca E. , Erickson Jacob H. , Moulton Jason L. , Barnett Melanie J. , Toman Carol J. , Long Sharon R.
Published: May 2008

A screen for novel symbiotic mutants of the nitrogen‐fixing legume symbiont Sinorhizobium meliloti uncovered a crucial role for the putative response regulator FeuP in the symbiotic infection process. Transcriptome analysis shows that FeuP controls the transcription of at least 16 genes, including ndvA, which encodes an ATP‐dependent exporter of cyclic β glucans. Loss of feuP function gives rise to traits associated with cyclic β glucan biosynthetic defects, including poor growth and motility under hypoosmotic conditions, and the inability to invade plant tissue during the early stages of symbiotic infection. Analysis of cyclic glucans indicates that the feuP mutant is able to synthesize intracellular cyclic β glucans, but is unable to export them. Cyclic β glucan export can be restored to feuP mutant cells by constitutive expression of ndvA; likewise, the symbiotic phenotype of a feuP mutant is rescued by ectopic ndvA expression. We further show that the linked sensor kinase gene, feuQ, is also important for modulating ndvA transcription, and that signalling through the FeuP/FeuQ pathway is responsive to extracellular osmotic conditions, with low osmolarity stimulating ndvA expression.
Repression of motility during fimbrial expression: identification of 14 mrpJ gene paralogues in Proteus mirabilis
Authors: Pearson Melanie M. , Mobley Harry L. T.
Published: May 2008

Proteus mirabilis alternates between motile and adherent forms. MrpJ, a transcriptional regulator previously reported to repress motility, is encoded at the 3′ end of the mrp fimbrial operon in P. mirabilis. Sequencing of the P. mirabilis genome revealed 14 additional paralogues of mrpJ, 10 of which are associated with fimbrial operons. Twelve of these genes, when overexpressed, repressed motility; several distinct patterns of swarming motility were noted. Expression of 10 of the 14 mrpJ paralogues repressed flagellin (FlaA) synthesis. Alignment of the predicted amino acid sequences of MrpJ and its 14 paralogues revealed a conserved consensus motif (SQQQFSRYE) within the helix‐turn‐helix domain. Site‐directed mutagenesis of these residues coupled with linker insertion mutagenesis of MrpJ confirmed the importance of this domain for repression of motility. Gel shift assays demonstrated that MrpJ and another paralogue UcaJ bind directly to the promoter region of the flagellar master regulator flhDC. Thus, P. mirabilis appears to use a related mechanism to inhibit motility during the production of at least 10 of its predicted fimbriae.
Identification of transcriptional activators for thienamycin and cephamycin C biosynthetic genes within the thienamycin gene cluster from Streptomyces cattleya
Authors: Rodríguez Miriam , Núñez Luz Elena , Braña Alfredo F. , Méndez Carmen , Salas José A. , Blanco Gloria
Published: May 2008

Two regulatory genes, thnI and thnU, were identified in the thienamycin (thn) gene cluster from Streptomyces cattleya. ThnI resembles LysR‐type transcriptional activators and ThnU belongs to the SARP family of transcriptional activators. Their functional role was established after independent inactivation by gene replacement together with transcriptional analysis involving reverse transcription polymerase chain reaction (RT‐PCR). Deletion of thnI abolished thienamycin production showing its involvement in thienamycin biosynthesis. Gene expression analysis applied to the thn gene cluster demonstrated that ThnI is a transcriptional activator essential for thienamycin biosynthesis that regulates the expression of nine genes involved in thienamycin assembly and export (thnH, thnJ, thnK, thnL, thnM, thnN, thnO, thnP and thnQ). Unexpectedly, the thnU disrupted mutant was not affected in thienamycin production but turned out to be essential for cephamycin C biosynthesis. Transcript analysis applied to early and late structural genes for cephamycin C biosynthesis (pcbAB and cmcI), revealed that ThnU is the transcriptional activator of these cephamycin C genes although they are not physically linked to the thn cluster. In addition, it was shown that deletion of thnI has an upregulatory effect on pcbAB and cmcI transcription consistent with a significant increase in cephamycin C biosynthesis in this mutant.
Lymphocyte hyporesponsiveness during filarial nematode infection
Authors: HARNETT W. , HARNETT M. M.
Published: May 2008

A frequently observed feature of active infection with filarial nematodes is the presence of lymphocytes in the bloodstream that have impaired responsiveness to antigen. It is generally accepted that such a defect in lymphocyte function could contribute to the failure of the immune system to eliminate filarial nematodes. For this reason, understanding the mechanism underlying lymphocyte ‘hyporesponsiveness’ is an important goal for immunologists who study filarial nematodes. Thus, although there has long been an interest in answering questions such as what stage(s) of the nematode causes hyporesponsiveness, more recently, lymphocyte hyporesponsiveness has been increasingly studied at the molecular level. The result of this is that we are now beginning to learn much of the nature and cause of phenotypic changes in the hyporesponsive lymphocyte and also of the identity of the nematode‐derived molecules that induce them. As this information continues to be generated, the challenge will be to use it to find a way of reversing lymphocyte hyporesponsiveness in the hope that this will lead to rejection of filarial nematodes in the parasitized human host.
Protective immunity induced by daily bites from irradiated mosquitoes infected with Plasmodium yoelii
Authors: WONG K. A. , ZHOU A. , RODRIGUEZ A.
Published: May 2008

Individuals in malaria endemic regions do not develop fully protective immune responses against Plasmodium liver stage infections. In high transmission areas, individuals can be exposed to more than two infective mosquito bites daily. Their exposure to Plasmodium sporozoites, therefore, is in the form of small and frequent doses. This is very different from individuals studied in controlled immunization trials where the delivery of large numbers of radiation‐attenuated sporozoites in a limited number of doses can induce sterile protective immunity. Using irradiated mosquitoes infected with Plasmodium yoelii 17XNL, we tested whether daily bites from a few mosquitoes can induce a protective immune response in mice. This immunization strategy successfully induced a protective response, preventing the development of liver stages when mice were challenged with nonirradiated sporozoites. These results provide further support for the development of liver stage vaccines. They are also a call for further study into why fully protective responses against the liver stage are not seen in individuals from endemic regions.
Contractile roots in succulent monocots: convergence, divergence and adaptation to limited rainfall
Authors: NORTH GRETCHEN B. , BRINTON ERIN K. , GARRETT TADAO Y.
Published: May 2008

Contractile roots (CRs) that pull shoots further down in the soil are a possible example of convergent evolution in two monocot families, the Agavaceae and the Asphodelaceae. The association between CRs, water uptake and habitat aridity was investigated for agaves, yuccas and aloes by assessing the occurrence of CRs and the amount of root contraction for glasshouse‐grown plants with respect to mean annual rainfall of their native habitats. Structural features of CRs as well as root hydraulic conductance were compared with those of non‐contractile roots (NCRs). CRs occurred in 55% of the 73 species examined, including 64% of the agaves and 85% of the yuccas, but in none of the aloes despite the occurrence of CRs in related genera. The phylogenetic distribution of CRs was consistent with multiple acquisitions or losses of the trait. The amount of root contraction showed a highly significant negative relationship with mean annual rainfall, although other environmental factors may also be important. Radial hydraulic conductance of the basal (contractile) zone exceeded that of the midroot zone for CRs; for NCRs, the opposite was true. Thus, CRs in the species examined may provide a mechanism for greater water uptake near the soil surface in regions with limited rainfall.
Do major oxide tectonic discrimination diagrams work? Evaluating new log‐ratio and discriminant‐analysis‐based diagrams with Indian Ocean mafic volcanics and Asian ophiolites
Authors: Sheth Hetu C.
Published: May 2008

Many geochemical diagrams exist that classify old volcanic terranes of ambiguous provenance into various modern plate tectonic settings, with variable success. Recently proposed diagrams, based on log‐ratios and linear discriminant analysis with large datasets of major oxides, were tested here with data for ocean island, arc and mid‐ocean ridge lavas from the Indian Ocean. Success rates are 45–100%, with misclassifications potentially caused by alteration, although alteration demonstrably need not cause misclassification. The diagrams were further applied to some Asian ophiolites, representing Tethyan and Indian ocean crusts, to see if the diagrams confirm their tectonic setting inferred from trace and isotopic data. Lower success rates (30–60%, but 75–100% for specific suites) are not surprising in view of the ubiquitous and complex alteration in ophiolites. Log‐ratio transformation and linear discriminant analysis appear to be powerful methods when discrimination diagrams are based on major oxide data alone.
IMAGING STUDY: Modulation of brain response to emotional images by alcohol cues in alcohol‐dependent patients
Authors: Gilman Jodi M. , Hommer Daniel W.
Published: May 2008

Alcohol is often used to modulate mood states. Alcohol drinkers report that they use alcohol both to enhance positive affect and to reduce dysphoria, and alcohol‐dependent patients specifically state reduction of negative affect as a primary reason for drinking. The current study proposes that alcohol cues may reduce negative affect in alcoholics. We used functional magnetic resonance imaging to examine brain activation in response to combination images that juxtaposed negative or positive International Affective Picture System (IAPS) images with an alcohol or non‐alcohol‐containing beverage. We found that in the absence of the alcohol cue, alcoholics showed more activation to negative than to positive images and greater activation than controls to negative images. When the IAPS images were presented with the alcohol cue, there was a decreased difference in activation between the positive and negative images among the alcoholics, and a decreased difference in response to the negative images between controls and alcoholics. Additionally, in the neutral‐beverage conditions, anxiety ratings significantly predicted activation in the right parahippocampal gyrus but did not predict activation when the alcohol cues were presented. In conclusion, the alcohol cues may have modulated cortical networks involved in the processing of emotional stimuli by eliciting a conditioned response in the alcoholics, but not in the controls, which may have decreased responsiveness to the negative images.
Use of pheromone mimic to cause the disintegration and collapse of colonies of tent caterpillars (Malacosoma spp.)
Authors: Fitzgerald T. D.
Published: May 2008

The disruption of the trail‐based communication system of eastern tent caterpillars (ETC) (Malacosoma americanum) and forest tent caterpillars (FTC) (M. disstria) by spraying host trees with a trail pheromone mimic caused the disintegration and collapse of young colonies. A 1‐ppm formulation of 5β‐cholestan‐3‐one or a control formulation was sprayed on trees either before or after eclosion of the caterpillars in the spring. For pre‐eclosion trials, an average of 92% of the FTC colonies on control trees, but only 17% of colonies on treated trees consisted of viable, cohesive aggregates when survival was assessed 5–23 days post‐spray. The remaining colonies had either completely disappeared or were reduced to small, disintegrated fragments. For the ETC, 100% of colonies on control trees and an average of 12% of colonies on treated trees consisted of cohesive aggregates inhabiting tents when survival was assessed 3–41 days post‐spray. The remaining colonies were completely destroyed, reduced to scattered individuals, or to small, disintegrated, shelter‐less fragments. For post‐eclosion trials with the FTC in which colonies were sprayed during their first or second larval stadium, an average of 63% of individuals in control groups but only 7% in treatment groups were still on the sprayed trees 5–18 days post‐spray. For the ETC, colonies were largely unaffected when trees were not sprayed until after the caterpillars had eclosed and established tents. For all trials, the loss of individuals on treated trees was largely attributable to the inability of dispersed and isolated first or second instar caterpillars to maintain secure purchase, causing them to fall from trees and perish. To our knowledge, this is the first study to investigate the potential of manipulating populations of pest species by interfering with a trail‐based, chemical communication system.
Insulin resistance in experimental alcohol‐induced liver disease
Authors: De La Monte Suzanne M , Yeon Jong‐Eun , Tong Ming , Longato Lisa , Chaudhry Rajeev , Pang Mao‐Yin , Duan Kevin , Wands Jack R.
Published: May 2008

Background and Aim:  Chronic ethanol consumption impairs liver regeneration due, in part, to inhibition of insulin signaling. This study characterizes the mechanisms and consequences of ethanol‐impaired insulin signaling in relation to oxidative injury and altered gene expression.

Methods:  Long‐Evans rats were fed for 8 weeks with isocaloric liquid diets containing 0% (control) or 37% ethanol (caloric content). Livers were used to examine histopathology, indices of oxidative stress, gene expression required for insulin and insulin‐like growth factor (IGF) signaling, insulin‐responsive gene expression, i.e. glyceraldehydes‐3‐phosphate dehydrogenase (GAPDH) and aspartyl‐asparaginyl‐β‐hydroxylase (AAH), and competitive equilibrium binding to the insulin, IGF‐I, and IGF‐II receptors.

Results:  Chronic ethanol exposure caused liver injury with increased hepatocellular steatosis, inflammation, apoptosis, and increased immunoreactivity for activated caspase‐3, 8‐hydroxy‐2′‐deoxyguanosine, and 4‐hydroxy‐2,3‐nonenol. These effects were associated with increased expression of IGF‐I receptor, IGF‐II, and IGF‐II receptor, and expression of IGF‐I, AAH, and GAPDH, which mediate energy metabolism and cell motility/remodeling, and reduced binding to the insulin receptor.

Conclusions:  Chronic ethanol‐induced liver injury causes insulin resistance with inhibition of insulin‐responsive genes needed for metabolism, remodeling, and regeneration. In contrast, the IGF‐I and IGF‐II signaling mechanisms remain relatively preserved, suggesting that insulin‐regulated hepatic functions may be selectively vulnerable to the toxic effects of ethanol.
Changing the pathogenetic roadmap of liver fibrosis? Where did it start; where will it go?
Authors: Gressner Olav A , Rizk Mohamed S , Kovalenko Evgeniya , Weiskirchen Ralf , Gressner Axel M
Published: May 2008

The pathophysiology of liver injury has attracted the interest of experimentalists and clinicians over many centuries. With the discovery of liver‐specific pericytes – formerly called fat‐storing cells, Ito‐cells, lipocytes, and currently designated as hepatic stellate cells (HSC) – the insight into the cellular and molecular pathobiology of liver fibrosis has evolved and the pivotal role of HSC as a precursor cell‐type for extracellular matrix–producing myofibroblasts has been established. Although activation and transdifferentiation of HSC to myofibroblasts is still regarded as the pathogenetic key mechanism of fibrogenesis, recent studies point to a prominent heterogeneity of the origin of myofibroblasts. Currently, the generation of matrix‐synthesizing fibroblasts by epithelial–mesenchymal transition, by influx of bone marrow–derived fibrocytes into damaged liver tissue, and by differentiation of circulating monocytes to fibroblasts after homing in the injured liver are discussed as important complementary mechanisms to enlarge the pool of (myo‐)fibroblasts in the fibrosing liver. Among the molecular mediators, transforming growth factor‐beta (TGF‐β) plays a central role, which is controlled by the bone‐morphogenetic protein (BMP)‐7, an important antagonist of TGF‐β action. The newly discovered pathways supplement the linear concept of HSC activation to myofibroblasts, point to fibrosis as a systemic response involving extrahepatic organs and reactions, add further evidence to a more or less uniform concept of organ fibrosis in general (e.g. liver, lung, kidney), and offer innovative approaches for the development of non‐invasive biomarkers and antifibrotic trials.