The role of growth hormone in neural development

Growth hormone (GH) is integrally involved in the development of the central nervous system (CNS), as well as during its recovery from injury, two processes that share many similarities and may influence CNS functionality. This review discusses some of the most recent findings in the field and, in particular, the ontogeny, distribution, regulation and putative functions of GH and its receptor within the CNS, particularly during development. The relative roles of peripheral GH, acting in part through insulin-like growth factor-I, and of the autocrine/paracrine GH system within the brain are considered. The potential role of GH as a therapeutic agent to influence brain development and function is discussed.     

Effects of dipole position,orientation and noise on the accuracy of EEG source localization

Background  

The electroencephalogram (EEG) reflects the electrical activity in the brain on the surface of scalp. A major challenge in this field is the localization of sources in the brain responsible for eliciting the EEG signal measured at the scalp. In order to estimate the location of these sources, one must correctly model the sources, i.e., dipoles, as well as the volume conductor in which the resulting currents flow. In this study, we investigate the effects of dipole depth and orientation on source localization with varying sets of simulated random noise in 4 realistic head models.     

Biological control of Chenopodium album L. in Europe

Ascochyta caulina (P. Karst) v.d. Aa and v. Kest is aplant pathogenic fungus which is specific to Chenopodium albumL. It has been suggested as a potential mycoherbicide to this weed,which is important and wide spread in arable crops throughout Europe. Toinvestigate its potential as a biocontrol agent, the fungus has beentested in glasshouse and field experiments. Formulations containingdifferent combinations of A. caulina conidia, the phytotoxinsfrom the fungus and low doses of herbicides have been tested.Significant improvement in the efficacy of the fungus was achieved inglasshouse trials with an aqueous formulation containing PVA(0.1% v/v), Psyllium (0.4% w/v), Sylgard 309(0.1% v/v), nutrients and conidia (5 ×10⁶/ml). The extracellular, hydrophilic phytotoxinsproduced by A. caulina were purified and their structuresdetermined. The main toxin, named ascaulitoxin, was characterised as theN²--D-glucopyranoside of the unusual bis-aminoacid2,4,7-triamino-5-hydroxyoctandioic acid. Two other toxins proved to betrans-4-amino-D-proline and the aglycone of ascaulitoxin. Thesetoxins have shown promising herbicidal properties. Field trials haveinvestigated the performance of A. caulina conidia applied atdifferent developmental stages of C. album either as a singletreatment or combined with sub-lethal doses of herbicides or with thefungal phytotoxins. With the available formulation, favourable weatherconditions are needed to obtain infection in the field. The efficacy ofthe strain of A. caulina used so far has proved to beinadequate to justify its development as a bioherbicide. This isprobably due to its low virulence.     

Genotypic diversity and environmental variability affect the invasibility of experimental plant populations

The world is experiencing increasing climatic variability, an ongoing loss of biodiversity and a growing spread of invasive species. Previous experimental studies demonstrated that the invasibility of plant populations is reduced with increasing resident genetic diversity and is promoted by environmental fluctuations, but their combined effect has so far not been considered. In a growth chamber experiment, we tested whether the genotypic diversity of experimental populations of Arabidopsis thaliana (1, 3 or 6 genotypes) and temperature fluctuations affect population invasion by Senecio vulgaris, and how these factors interact. We found that genotypic diversity tended to increase the invasion resistance of experimental plant populations in terms of the biomass ratio between the species, and that temperature fluctuations strongly favoured Arabidopsis (biomass: +49%) over Senecio (–28%). However, there were no interactions between environmental fluctuations and genotypic diversity. Nevertheless, the magnitude of net diversity effects and transgressive overyielding depended on temperature conditions, indicating that increased environmental variability can influence diversity mechanisms. Our study shows that, although genotypic diversity and environmental variability did not interact, these two factors independently affected the invasibility of plant populations.     

Molecular mechanism of ligand recognition by membrane transport protein,Mhp1

The hydantoin transporter Mhp1 is a sodium‐coupled secondary active transport protein of the nucleobase‐cation‐symport family and a member of the widespread 5‐helix inverted repeat superfamily of transporters. The structure of Mhp1 was previously solved in three different conformations providing insight into the molecular basis of the alternating access mechanism. Here, we elucidate detailed events of substrate binding, through a combination of crystallography, molecular dynamics, site‐directed mutagenesis, biochemical/biophysical assays, and the design and synthesis of novel ligands. We show precisely where 5‐substituted hydantoin substrates bind in an extended configuration at the interface of the bundle and hash domains. They are recognised through hydrogen bonds to the hydantoin moiety and the complementarity of the 5‐substituent for a hydrophobic pocket in the protein. Furthermore, we describe a novel structure of an intermediate state of the protein with the external thin gate locked open by an inhibitor, 5‐(2‐naphthylmethyl)‐L‐hydantoin, which becomes a substrate when leucine 363 is changed to an alanine. We deduce the molecular events that underlie acquisition and transport of a ligand by Mhp1.     

SKPDB: a structural database of shikimate pathway enzymes

Background  

The functional and structural characterisation of enzymes that belong to microbial metabolic pathways is very important for structure-based drug design. The main interest in studying shikimate pathway enzymes involves the fact that they are essential for bacteria but do not occur in humans, making them selective targets for design of drugs that do not directly impact humans.     

Variation in regrowth ability in relation to land-use intensity in three common grassland herbs

3种常见草原草本植物的再生能力随土地利用强度的变异 在人工管理的草原上，植物种群受到放牧、刈割和施肥的强烈选择。以往的许多研究表明，这可能会导致性状平均值的进化性变化，但是人们对响应土地利用的表型可塑性的进化了解甚少。在本研究中，我们旨在阐明表型可塑性(特别是在生物量去除后的再生能力)与草原管理强度本身及其时间变化水平之间的关系。我们通过野外同质园实验，检测了来自高强度刈割和放牧地点的植物是否在生物量去除后有更强的再生能力。我们选用了源自欧洲温带草原的3种常见的植物物种，其种子材料来自沿土地利用强度梯度的58–68个种群，对应的土地利用方式由粗放式管理(仅有轻度的放牧)过渡到非常集约式管理(多达每年4次收割)。研究结果表明，3个物种当中的两种在刈割后的再生能力存在显著的种群差异。虽然再生能力的变异与种群原生地的平均土地利用强度无关，但是我们发现长叶车前(Plantago lanceolata)的再生能力与土地利用强度的时间变化相关。在过去11年中，经历了较小环境条件变化的植物在刈割之后有较强的生殖生物量再生能力。因此，尽管平均的放牧和刈割强度可能不会对再生能力造成选择，但是土地利用所导致的环境异质性的时间稳定性可能会造成某些物种再生能力的进化。     

Mitochondrial DNA differentiation during the speciation process in Peromyscus

We address the problem of the possible significance of biological speciation to the magnitude and pattern of divergence of asexually transmitted characters in bisexual species. The empirical data for this report consist of restriction endonuclease site variability in maternally transmitted mitochondrial DNA (mtDNA) isolated from 82 samples of Peromyscus polionotus and P. leucopus collected from major portions of the respective species' ranges. Data are analyzed together with previously published information on P. maniculatus, a sibling species to polionotus. Maps of restriction sites indicate that all of the variation observed can be reasonably attributed to base substitutions leading to loss or gain of particular recognition sites. Magnitude of mtDNA sequence divergence within polionotus (maximum approximately equal to 2%) is roughly comparable to that observed within any of five previously identified mtDNA assemblages in maniculatus. Sequence divergence within leucopus (maximum approximately equal to 4%) is somewhat greater than that within polionotus. Consideration of probable evolutionary links among mtDNA restriction site maps allowed estimation of matriarchal phylogenies within polionotus and leucopus. Clustering algorithms and qualitative Wagner procedures were used to generate phenograms and parsimony networks, respectively, for the between-species comparisons. Three simple graphical models are presented to illustrate some conceivable relationships of mtDNA differentiation to speciation. In theoretical case I, each of two reproductively defined species (A and B) is monophyletic in matriarchal genealogy; the common female ancestor of either species can either predate or postdate the speciation. In case II, neither species is monophyletic in matriarchal genotype. In case III, species B is monophyletic but forms a subclade within A which is thus paraphyletic with respect to B. The empirical results for mtDNA in maniculatus and polionotus appear to conform closely to case III. These theoretical and empirical considerations raise a number of questions about the general relationship of the speciation process to the evolution of uniparentally transmitted traits. Some of these considerations are presented, and it is suggested that the distribution patterns of mtDNA sequence variation within and among extant species should be of considerable relevance to the particular demographies of speciation.      

Distribution of bulbil- and seed-producing plants of Poa alpina (Poaceae) and their growth and reproduction in common gardens suggest adaptation to different elevations

• Premise of the study: The European Alps harbor a spatially heterogeneous environment. Plants can be adapted genetically to this heterogeneity but may also respond to it by phenotypic plasticity. We expected the important fodder grass Poa alpina to be adapted to elevation either genetically or plastically. • Methods: We investigated in three elevational common gardens whether growth and reproductive allocation of plants reproducing either by seeds or bulbils suggest adaptation to their elevation of origin and to what extent they can respond plastically to different elevations. Additionally, we analyzed genetic diversity using microsatellites and tested whether seeds are of sexual origin. • Key results: In the field, bulbil-producing plants occurred more often at higher elevations, whereas seed-producing plants occurred more often at lower elevations, but bulbil-producing plants were generally less vigorous in the common gardens. The response of plants to elevational transplantation was highly plastic, and vigor was always best at the highest location. The small genetic differences were not clinally related to elevation of origin, underlining the importance of phenotypic plasticity. Reproductive allocation was, however, independent of elevational treatments. Seed-producing plants had higher genetic diversity than the bulbil-producing plants even though we found that seed-producing plants were facultative apomicts mostly reproducing asexually. • Conclusions: Bulbil-producing P. alpina, showing a fitness cost at lower elevations compared with seed-producing plants, seem better adapted to higher elevations. By means of its two reproductive modes and the capacity to adjust plastically, P. alpina is able to occupy a broad ecological niche across a large elevational range.