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Selected AbstractsEffects of substrate geometry on growth cone behavior and axon branchingDEVELOPMENTAL NEUROBIOLOGY, Issue 11 2006Ginger S. Withers Abstract At the leading edge of a growing axon, the growth cone determines the path the axon takes and also plays a role in the formation of branches, decisions that are regulated by a complex array of chemical signals. Here, we used microfabrication technology to determine whether differences in substrate geometry, independent of changes in substrate chemistry, can modulate growth cone motility and branching, by patterning a polylysine grid of narrow (2 or 5 ,m wide) intersecting lines. The shape of the intersections varied from circular nodes 15 ,m in diameter to simple crossed lines (nodeless intersections). Time-lapse recordings of cultured hippocampal neurons showed that simple variations in substrate geometry changed growth cone shape, and altered the rate of growth and the probability of branching. When crossing onto a node intersection the growth cone paused, often for hours, and microtubules appeared to defasciculate. Once beyond the node, filopodia and lamellipodia persisted at that site, sometimes forming a collateral branch. At nodeless intersections, the growth cone passed through with minimal hesitation, often becoming divided into separate areas of motility that led to the growth of separate branches. When several lines intersected at a common point, growth cones sometimes split into several subdivisions, resulting in the emergence of as many as five branches. Such experiments revealed an intrinsic preference for branches to form at angles less than 90°. These data show that simple changes in the geometry of a chemically homogeneous substrate are detected by the growth cone and can regulate axonal growth and the formation of branches. © 2006 Wiley Periodicals, Inc. J Neurobiol 66: 1183,1194, 2006 [source] Are there general mechanisms of animal home range behaviour?ECOLOGY LETTERS, Issue 6 2008A review, prospects for future research Abstract Home range behaviour is a common pattern of space use, having fundamental consequences for ecological processes. However, a general mechanistic explanation is still lacking. Research is split into three separate areas of inquiry , movement models based on random walks, individual-based models based on optimal foraging theory, and a statistical modelling approach , which have developed without much productive contact. Here we review recent advances in modelling home range behaviour, focusing particularly on the problem of identifying mechanisms that lead to the emergence of stable home ranges from unbounded movement paths. We discuss the issue of spatiotemporal scale, which is rarely considered in modelling studies, as well as highlighting the need to consider more closely the dynamical nature of home ranges. Recent methodological and theoretical advances may soon lead to a unified approach, however, conceptually unifying our understanding of linkages among home range behaviour and ecological or evolutionary processes. [source] Intrafamilial Transmission of Helicobacter pylori among the Population of Endemic Areas in JapanHELICOBACTER, Issue 2 2007Yayoi Fujimoto Abstract Background:,Helicobacter pylori (H. pylori) infection is a worldwide phenomenon related to several gastrointestinal diseases. However, because many aspects concerning the route of transmission remain unclear, we performed this epidemiologic study to clarify the route of intrafamilial transmission of H. pylori. Materials and Methods:, A retrospective study was performed in three widely separate areas in Japan to investigate the prevalence of H. pylori infection. In 1993, 613 residents were tested as were 4136 in 2002, including 1447 family members of 625 families. Antibody to H. pylori (anti- H. pylori) was determined by enzyme-linked immunosorbent assay. Results:, In 2002, the age-adjusted anti- H. pylori prevalence in Hoshino Village (67.5%) was significantly higher than in Kasuya Town (55.0%) and in Ishigaki City (54.7%) (p < .0001, p = .0039, respectively). The age-adjusted anti- H. pylori prevalence of Ishigaki City significantly decreased from 1993 (68.4%) to 2002 (52.5%), showing an age cohort effect. However, the prevalence did not significantly differ in children aged 0,6 years of Ishigaki City between 1993 (9.6%) and 2002 (10.3%). A familial analysis in 2002 demonstrated that the prevalence of anti- H. pylori was significantly higher in children with anti- H. pylori -positive (21.6%, 22 of 102) than with -negative mothers (3.2%, 3 of 95) (p < .0001, by Mantel,Haenszel test), whereas there was no significant difference between children with anti- H. pylori -positive and -negative fathers. Moreover, the prevalence was significantly higher in wives with anti- H. pylori -positive (64.0%, 208 of 325) than with -negative husbands (46.5%, 80 of 172) (p = .0071, by Mantel,Haenszel test) and in husbands with anti- H. pylori -positive (72.2%, 208 of 288) than with -negative wives (56.0%, 117 of 209) (p = .0106, by Mantel,Haenszel test). Conclusions:, In the last decade, H. pylori infection decreased in the general population of Japan by improvement of general hygiene conditions, but did not differ in young children, most likely because of mother-to-child transmission. [source] Dry spots and wet spots in the Andean hotspotJOURNAL OF BIOGEOGRAPHY, Issue 8 2007Timothy J. Killeen Abstract Aim, To explain the relationship between topography, prevailing winds and precipitation in order to identify regions with contrasting precipitation regimes and then compare floristic similarity among regions in the context of climate change. Location, Eastern slope of the tropical Andes, South America. Methods, We used information sources in the public domain to identify the relationship between geology, topography, prevailing wind patterns and precipitation. Areas with contrasting precipitation regimes were identified and compared for their floristic similarity. Results, We identify spatially separate super-humid, humid and relatively dry regions on the eastern slope of the Andes and show how they are formed by the interaction of prevailing winds, diurnally varying atmospheric circulations and the local topography of the Andes. One key aspect related to the formation of these climatically distinct regions is the South American low-level jet (SALLJ), a relatively steady wind gyre that flows pole-ward along the eastern slopes of the Andes and is part of the gyre associated with the Atlantic trade winds that cross the Amazon Basin. The strongest winds of the SALLJ occur near the ,elbow of the Andes' at 18° S. Super-humid regions with mean annual precipitation greater than 3500 mm, are associated with a ,favourable' combination of topography, wind-flow orientation and local air circulation that favours ascent at certain hours of the day. Much drier regions, with mean annual precipitation less than 1500 mm, are associated with ,unfavourable' topographic orientation with respect to the mean winds and areas of reduced cloudiness produced by local breezes that moderate the cloudiness. We show the distribution of satellite-estimated frequency of cloudiness and offer hypotheses to explain the occurrence of these patterns and to explain regions of anomalously low precipitation in Bolivia and northern Peru. Floristic analysis shows that overall similarity among all circumscribed regions of this study is low; however, similarity among super-humid and humid regions is greater when compared with similarity among dry regions. Spatially separate areas with humid and super-humid precipitation regimes show similarity gradients that are correlated with latitude (proximity) and precipitation. Main conclusions, The distribution of precipitation on the eastern slope of the Andes is not simply correlated with latitude, as is often assumed, but is the result of the interplay between wind and topography. Understanding the phenomena responsible for producing the observed precipitation patterns is important for mapping and modelling biodiversity, as well as for interpreting both past and future climate scenarios and the impact of climate change on biodiversity. Super-humid and dry regions have topographic characteristics that contribute to local climatic stability and may represent ancestral refugia for biodiversity; these regions are a conservation priority due to their unique climatic characteristics and the biodiversity associated with those characteristics. [source] GIS and spatial data analysis: Converging perspectivesPAPERS IN REGIONAL SCIENCE, Issue 1 2004Michael F. Goodchild GIS; spatial data analysis; spatial modelling; geostatistics; point processes Abstract. This article identifies some of the important developments in GIS and spatial data analysis since the early 1950s. Although GIS and spatial data analysis started out as two more or less separate areas of research and application, they have grown closer together over time. We argue that the two areas meet in the field of geographic information science, with each supporting and adding value to the other. The article starts off providing a critical retrospective of developments over the past 50 years. Subsequently, we reflect on current challenges and speculate about the future. Finally, we comment on the potential for convergence of developments in GIS and spatial data analysis under the rubric of geographic information science (GIScience). [source] The National Integrity System: assessing corruption and reformPUBLIC ADMINISTRATION & DEVELOPMENT, Issue 4 2003Alan Doig This article builds on a Transparency International (TI)-sponsored research study funded by the Dutch Government into the National Integrity System (NIS) in practice. The NIS is a framework approach developed by TI that proposes assessing corruption and reform holistically. The NIS not only looks at separate institutions or separate areas of activity or separate rules and practices, but also bases its perspective on institutional and other inter-relationships, inter-dependence and combined effectiveness. The study involved 18 countries, using in-country researchers and an overview report. This article assesses the findings of the study to consider how the approach can work in practice, and what the approach can reveal about the causes and nature of corruption as well as the implications for reform. Copyright © 2003 John Wiley & Sons, Ltd. [source] Different Gene Expressions on the Left and the Right: A Genotype/Phenotype Mismatch in Need of AttentionANNALS OF HUMAN GENETICS, Issue 1 2008Ursula Mittwoch Summary Discordance in monozygotic twins has traditionally been explained in terms of environmental influences. A recent investigation has found a difference in epigenetic markers in older but not in younger twins. However, phenotypic differences that depend on an individual's postnatal life style do not address the problem of discordance in congenital malformations, or the reason why malformations are frequently unilateral, often with a preference for one or the other side. One such condition, cleft lip with or without cleft palate, which is preferentially expressed on the left, is a multifactorial condition, that is caused by a failure of the critical timing necessary for different groups of cells to meet and develop into a normal face. This process is dependent on cell proliferation and migration, which are energy-dependent, while the additional requirement for apoptosis to allow cell fusion suggests the involvement of mitochondria. Recent progress in two separate areas of research could lead to a better understanding of the problem of facial clefts: (1) the recognition of an interaction between gene products and mitochondria in the aetiology of neurodegenerative diseases and (2) the discovery of an increasing number of genes, including transcription factors, growth factors and members of the TGF-, signalling family, that are differentially expressed on the left and right side, thus pointing to a difference in their micro-environment. These findings emphasize the importance of investigating the activity of candidate genes for complex developmental processes separately on the left and right sides. Data presented in this review suggest that differential growth rates may lead to an inversion of laterality. A method is described to test for a possible mitochondrial difference between left and right sides, using a mouse model with cleft lip. [source] | |||||||||||||