Trafficking and localisation of resident Golgi glycosylation enzymes

The localisation of glycosylation enzymes within the Golgi apparatus is fundamental to the regulation of glycoprotein and glycolipid biosynthesis. Regions responsible for specifying Golgi localisation have been identified in numerous Golgi resident enzymes. The transmembrane domain of Golgi glycosyltransferases provides a dominant localisation signal and in many cases there are also major contributions from the lumenal domain. The mechanism by which these targeting domains function in maintaining an asymmetric distribution of Golgi resident glycosylation enzymes has been intensely debated in recent years. It is now clear that the targeting of Golgi resident enzymes is intimately associated with the organisation of Golgi membranes and the control of protein and lipid traffic in both anterograde and retrograde directions. Here we discuss the recent advances into how Golgi targeting signals of glycosylation enzymes function, and propose a model for maintaining the steady-state localisation of Golgi glycosyltransferases.     

Autophagy: a new player in hepatic stellate cell activation

Hepatic stellate cell (HSC) activation, the transition from a resident quiescent HSC to a myofibroblastic collagen-producing HSC, is a fundamental feature of liver fibrosis. Autophagy has been implicated in major liver pathologies, such as HCV infection and hepatocarcinoma. However, its role in HSC biology is largely unknown. Recently, we were able to demonstrate that HSC activation is followed by an increased autophagic flux and that its inhibition can partially inhibit the HSC myofibroblastic transition. These results point to autophagy as a possible target in the prevention of HSC activation.     

Acoustic Competition in Male Midwife Toads Alytes obstetricans and Alytes cisternasii: Response to Neighbor Size and Calling Rate. Implications for Female Choice

Effects of neighbor on male calling behavior was studied through playback experiments of synthetic calls to males of two species of midwife toads. The responses of resident males were scored considering two temporal parameters (call duration and calling rate) and one spectral parameter (dominant frequency). The sounds used for the playback tests included two levels of fundamental frequency (correlated with male size) and two levels of call repetition rate. In both species, resident males only changed their calling rate in the presence of an intruder, and the response was different for synthetic calls with two levels of dominant frequencies and with two calling rates. Resident size was not significantly correlated with the magnitude of the change in the calling rate. On the other hand, resident calling rate was significantly and positively correlated with the magnitude of the increase in calling rate of the stimulus. The maximum relative increase in calling rate was observed in A. cisternasii. In phonotaxis tests, females are preferentially attracted to calls emitted at a higher rate confirming the importance of changes in calling rate for female attraction.     

Stem cells to tissue: molecular,cellular and anatomical heterogeneity in skeletal muscle

Multiple waves of muscle precursors are released from skeletal muscle progenitor cells throughout developmental life, and this process is initiated in precise locations in the embryo. Skeletal muscle diversifies not only after the acquisition of muscle identity, but curiously heterogeneity is observed even in the stem cell population. Recent studies on cell lineage, cell fusion and the nature of post-natal satellite cells have expanded on our fundamental knowledge of the formation of this tissue, and how this tissue is replenished by resident and circulating regenerative stem cells during adult life.     

Every Coin Has a Back Side: Invasion by Limnohabitans planktonicus Promotes the Maintenance of Species Diversity in Bacterial Communities

One of the earliest challenges for ecologists has been to study the impact of invasive species on microbial communities. Although bacteria are fundamental in biological processes, current knowledge on invasion effects by aquatic non-pathogenic bacteria is still limited. Using pure cultures of diverse planktonic bacteria as model organisms at two different carbon concentration levels, we tested the response of an assembled community to the invasion by Limnohabitans planktonicus, an opportunistic bacterium, successful in freshwaters. The invader, introduced at the early stationary growth phase of the resident community, caused a strong decrement of the abundance of the dominant species. This was due to competition for nutrients and a potential allelopathic interaction. Simultaneously, resident species formerly unable to successfully compete within the community, thus potentially exposed to competitive exclusion, increased their abundances. The overall result of the invasion was preservation of species diversity, the higher the lower was the substrate content available. Our study provides new insights into bacterial invasions, offering an alternative interpretation of invasions for community ecology.     

Principles of hepatocyte repopulation

Hepatocyte transplantation (HTx) is technically feasible and can be clinically beneficial. Current research focuses on optimizing parameters which relate to the outcome of HTx, including site of transplantation, cell number and, most notably, the preferred cell type to be transplanted (differentiated adult vs. fetal hepatocytes vs. putative progenitor or precursor cells). However, the single major impediment towards the clinical effectiveness of HTx is the limited expansion of donor cells in the recipient liver. To this end, a relative growth advantage must be present or is to be imposed on transplanted hepatocytes versus resident cells. Possible strategies are presented and discussed.     

A stereological ultrastructural study of stimulated peritoneal macrophages in the germ-free mouse

Peritoneal macrophage ultrastructure was analysed stereologically in germ-free mice given a single intraperitoneal injection of sterile, pyrogen-free saline. Thus the stimulant was non-particulate, non-antigenic and inorganic, and effects of immune reactions were minimal. Macrophages were recovered 1, 6, 24 and 72 h after stimulation. A sequence of structural alterations is reported which may be fundamental to macrophage activation. The plasma membrane and nuclear envelope increased in area within only 1 h of saline injection. During the next 5 h loss of plasma membrane, probably by pinocytosis, caused cellular "rounding" and clear-cut alteration in surface configuration. At the same time lysosome-like granules enlarged but decreased in number. By 24 h most cellular structures and compartments (including the plasma membrane) were enlarged. Morphological evidence of nuclear activation accompanied a rather modest enlargement of the nucleus at this stage. The RER hypertrophied last and must, therefore, be judged sufficient in resident macrophages to support the initial growth response which results after stimulation. Thus hypertrophy was observed eventually in every structure examined. Even the minimally activated macrophages resident in the peritoneum of germ-free mice respond readily to stimulation.     

A quantitative threshold for nest-mate recognition in a paper social wasp

Nest-mate recognition is fundamental for protecting social insect colonies from intrusion threats such as predators or social parasites. The aggression of resident females towards intruders is mediated by their cuticular semiochemicals. A positive relation between the amount of cues and responses has been widely assumed and often taken for granted, even though direct tests have not been carried out. This hypothesis has important consequences, since it is the basis for the chemical insignificance strategy, the most common explanation for the reduction in the amount of semiochemicals occurring in many social parasites. Here we used the social wasp Polistes dominulus, a model species in animal communication studies and host of three social parasites, to test this hypothesis. We discovered that different amounts of cuticular hydrocarbons (CHC) of a foreign female evoke quantitatively different behavioural reactions in the resident foundress. The relation between CHC quantity and the elicited response supports the idea that a threshold exists in the chemical recognition system of this species. The chemical insignificance hypothesis thus holds in a host–parasite system of Polistes wasps, even though other explanations should not be discarded.     

Interpreting the protein language using proteomics

Post-translational modifications define the functional and structural plasticity of proteins in archaea, prokaryotes and eukaryotes. Multi-site protein modification modulates protein activity and macromolecular interactions and is involved in a range of fundamental molecular processes. Combining state-of-the-art technologies in molecular cell biology, protein mass spectrometry and bioinformatics, it is now feasible to discover and study the structural and functional roles of distinct protein post-translational modifications.     

Punishment of polygyny

We investigated the evolution of monogamy (one male, one female) and polygyny (one male, more than one female). In particular, we studied whether it is possible for a mutant polygynous mating strategy to invade a resident population of monogamous breeders and, alternatively, whether a mutant monogamy can invade resident polygyny. Our population obeys discrete-time Ricker dynamics. The role of males and females in the breeding system is incorporated via the harmonic birth function. The results of the invasability analysis are straightforward. Polygyny is an evolutionarily stable strategy mating system; this holds throughout the examined range of numbers of offspring produced per female. So that the two strategies can coexist, polygyny has to be punished. The coexistence of monogamy and polygyny is achieved by reducing the offspring number for polygyny relative to monogamy. This yields long-term persistence of the strategies for all offspring numbers studied. An alternative punishment is to increase the sensitivity of polygynous breeders to population density. The coexistence is possible only with a limited range of offspring produced. The third way to achieve coexistence of the two mating strategies is to assume that individuals live in a spatially structured population, where dispersal links population subunits to a network. Reducing the dispersal rate of polygynous breeders relative to that of monogamous individuals makes the coexistence feasible. However, for monogamy to persist, the number of offspring produced has to be relatively high.     

Competition and body size in plants: the between-species trade-off for maximum potential versus minimum reproductive threshold size

Aims According to traditional theory, superior competitive ability in plants generally requires relatively large plant body size. Yet even within the most crowded vegetation, most resident species are relatively small; species size distributions are right-skewed at virtually every scale. We examine a potential explanation for this paradox: small species coexist with and outnumber large species because they have greater 'reproductive economy', i.e. they are better equipped—and hence more likely—to produce offspring despite severe size suppression from intense competition.Methods Randomly placed plots within old-field vegetation were surveyed across the growing season. Within each plot, the largest (MAX) and smallest (MIN) reproductive individuals of each resident species were collected for above-ground dry mass measurement. We tested three hypotheses: (i) smaller resident species (with smaller MAX size) have generally smaller reproductive threshold sizes; (ii) smaller resident species have greater 'reproductive economy', i.e. a smaller MIN relative to MAX reproductive plant size; and (iii) MIN size predicts plot occupancy (species abundance within the community) better than MAX size.Important findings The results supported the first and third, but not the second hypothesis. However, we could not reject the hypothesis that smaller species have greater reproductive economy, as it was not possible to record data for the largest potential plant size for each species—since even the largest (MAX) plants collected from our sampled plots were subjected to competition from neighbours under these natural field conditions. Importantly, contrary to conventional competition theory, more successful species (in terms of greater plot occupancy) had smaller minimum not larger (or smaller) maximum reproductive sizes. These results suggest that a small reproductive threshold size, commonly associated with relatively small potential body size, is generally more effective in transmitting genes into future generations when selection from neighbourhood crowding/competition is intense—at least within natural old-field vegetation. Accordingly, we propose a simple conceptual model that represents the basis for a fundamental paradigm shift in the predicted selection effects of crowding/competition on plant body size evolution.     

Evolution of Dispersal in a Structured Metapopulation Model in Discrete Time

In this article, a structured metapopulation model in discrete time with catastrophes and density-dependent local growth is introduced. The fitness of a rare mutant in an environment set by the resident is defined, and an efficient method to calculate fitness is presented. With this fitness measure evolutionary analysis of this model becomes feasible. This article concentrates on the evolution of dispersal. The effect of catastrophes, dispersal cost, and local dynamics on the evolution of dispersal is investigated. It is proved that without catastrophes, if all population–dynamical attractors are fixed points, there will be selection for no dispersal. A new mechanism for evolutionary branching is also found: Even though local population sizes approach fixed points, catastrophes can cause enough temporal variability, so that evolutionary branching becomes possible.     

Light Amplification with Low-Gain Material: Harvesting Harmonic Resonance Modes of Surface Plasmon Polaritons on a Magnetic Meta-Surface

We theoretically show that it is feasible to utilize harmonic resonance modes of surface plasmon polaritons on a magnetic meta-surface for light amplification with low-gain material. The required threshold and optimal gain strength for active layer can be substantially reduced to about one-tenth as compared with those utilizing fundamental resonance modes. The findings provide a simple and practical metamaterial approach for light amplification with most of the existing active media.     

Mammal population regulation, keystone processes and ecosystem dynamics

The theory of regulation in animal populations is fundamental to understanding the dynamics of populations, the causes of mortality and how natural selection shapes the life history of species. In mammals, the great range in body size allows us to see how allometric relationships affect the mode of regulation. Resource limitation is the fundamental cause of regulation. Top-down limitation through predators is determined by four factors: (i). body size; (ii). the diversity of predators and prey in the system; (iii). whether prey are resident or migratory; and (iv). the presence of alternative prey for predators. Body size in mammals has two important consequences. First, mammals, particularly large species, can act as keystones that determine the diversity of an ecosystem. I show how keystone processes can, in principle, be measured using the example of the wildebeest in the Serengeti ecosystem. Second, mammals act as ecological landscapers by altering vegetation succession. Mammals alter physical structure, ecological function and species diversity in most terrestrial biomes. In general, there is a close interaction between allometry, population regulation, life history and ecosystem dynamics. These relationships are relevant to applied aspects of conservation and pest management.     

Invasion dynamics and attractor inheritance

 We study the dynamics of a population of residents that is being invaded by an initially rare mutant. We show that under relatively mild conditions the sum of the mutant and resident population sizes stays arbitrarily close to the initial attractor of the monomorphic resident population whenever the mutant has a strategy sufficiently similar to that of the resident. For stochastic systems we show that the probability density of the sum of the mutant and resident population sizes stays arbitrarily close to the stationary probability density of the monomorphic resident population. Attractor switching, evolutionary suicide as well as most cases of ``the resident strikes back' in systems with multiple attractors are possible only near a bifurcation point in the strategy space where the resident attractor undergoes a discontinuous change. Away from such points, when the mutant takes over the population from the resident and hence becomes the new resident itself, the population stays on the same attractor. In other words, the new resident ``inherits' the attractor from its predecessor, the former resident. Received: 10 December 2000 / Revised version: 14 September 2001 / Published online: 17 May 2002     

Mechanisms of homology-facilitated illegitimate recombination for foreign DNA acquisition in transformable Pseudomonas stutzeri

Intra- and interspecific natural transformation has been observed in many prokaryotic species and is considered a fundamental mechanism for the generation of genetic variation. Recently, it has been described in detail how, in transformable Acinetobacter BD413 and Streptococcus pneumoniae, long stretches of nucleotides lacking homology were integrated into recipient genomes when they were linked on one side to a small piece of DNA with homology to resident DNA serving as a recA-dependent recombination anchor. Now, such homology-facilitated illegitimate recombination (HFIR) has also been detected in transformable Pseudomonas stutzeri. However, analysis of the recombinants revealed qualitative and quantitative differences in their generation compared with that in Acinetobacter BD413. In P. stutzeri, foreign DNA with an anchor sequence was integrated 105- to 106-fold less frequently than fully homologous DNA, but still at least 200-fold more frequently than without the anchor. The anchor sequence could be as small as 311 bp. Remarkably, in 98% of the events, the 3' end was integrated within the homologous anchor, whereas the 5' end underwent illegitimate fusion. Moreover, about one-third of the illegitimate fusion sites shared no or only a single identical basepair in foreign and resident DNA. The other fusions occurred within microhomologies of up to 6 bp with a higher GC content on average than the interacting nucleotide sequences. Foreign DNA of 69-1903 bp was integrated, and resident DNA of 22-2345 bp was lost. In a recA mutant, HFIR was not detectable. The findings suggest that genomic acquisition of foreign DNA by HFIR during transformation occurs widely in prokaryotes, but that details of the required recombination and strand fusion mechanisms may differ between organisms from different genera.     

Controlling small mammal predators using sodium monofluoroacetate (1080) in bait stations along forestry roads in a New Zealand beech forest

A single five night pulse of sodium monofluroacetate (0.15% 1080) applied in bait stations at two different spacing intervals, 100 and 200 m, along forestry roads in New Zealand beech forest, killed all four of the resident radio-tagged stoats (Mustela erminea) and all three of the resident radio- tagged wild house cats (Felis catus) by secondary poisoning. Gut contents of predators indicated that house mice (Mus musculus), ship rats (Rattus rattus) and bushtail possums (Trichosurus vulpecula) were important sources of the toxin. High kills of predators, possums and rats at both 100 and 200 m spacing regimes suggest that greater efficacy of controlling these pests would be achieved with the latter method. Evidence suggests that routine management of possums and rats using 1080 and brodifacoum has resulted in widespread control of small mammalian carnivores by secondary poisoning in New Zealand forests. However, aerial application of poison can kill large numbers of tomtits (Petroica macrocephala) and robins (Petroica australis) and few other native bird species have been adequately monitored through such operations. Reducing risks to native wildlife is responsible ecological management. Use of bait stations along forestry roads or tracks may be fundamental in mounting cost-effective :Large-scale ground-based protection of native wildlife through safer predator controls.     

用巢式PCR检测育龄妇女人群人细小病毒B19感染的研究

目的调查人类细小病毒B19在武汉地区普通人群,尤其是育龄妇女中的感染状况。方法采集武汉地区2家医院的血液样本1700份,分为两组。以血清中提取的DNA为模板,进行巢式PCR扩增。结果第Ⅰ组（普通组,包括男性和女性）阳性检测率为4．50％,第Ⅱ组（妇女组）阳性检测率为8．33％。结论武汉地区育龄妇女的B19感染率高于普通人群,很有必要对孕妇进行诊断从而预防新生儿感染B19病毒。另外,由于巢式PCR具有灵敏、特异、简便等优点,适合于用来检测血液样本中的人细小病毒B19。     

Mini-CEX 在住院医师培养中的应用现状

住院医师培养制度现已逐步在中国各城市开始实施,住院医师培养最主要的目标是培养临床能力合格的医师。对住院医师临床能力的评估,最好的方式应该是在临床的实践工作中的给予评估。Mini-CEX(Mini-Clinical Evaluation Exercise)是在传统的CEX基础上,发展出的一套用来评估住院医师临床技能并具有教学功能的测评工具,包括观察和评价住院医师的知识、技能、态度和主治医师的适时反馈。Mini-CEX为一种迷你型的多次重点式评估,在门诊、急诊或住院等临床例行工作中均可以开展,具备相当可靠的信效度和极好的便利性。Mini-CEX具有一个参与双方的信息及时反馈。应用Mini-CEX能增强评估的科学性,并能促进学习和培训。Mini-CEX作为目前医学教育体系中应用最广泛的一种评估手段之一,受到了国内外医学教育工作者的关注,并开始逐渐引入我国。Mini-CEX将在中国住院医师培养制度中发挥非常重要的作用。     

Fundamental clusters in spatial 2x2 games

The notion of fundamental clusters is introduced, serving as a rule of thumb to characterize the statistical properties of the complex behaviour of cellular automata such as spatial 2 x 2 games. They represent the smallest cluster size determining the fate of the entire system. Checking simple growth criteria allows us to decide whether the cluster-individuals, e.g. some mutant family, are capable of surviving and invading a resident population. In biology, spatial 2 x 2 games have a broad spectrum of applications ranging from the evolution of cooperation and intraspecies competition to disease spread. This methodological study allows simple classifications and long-term predictions in various biological and social models to be made. For minimal neighbourhood types, we show that the intuitive candidate, a 3 x 3 cluster, turns out to be fundamental with certain weak limitations for the Moore neighbourhood but not for the Von Neumann neighbourhood. However, in the latter case, 2 x 2 clusters generally serve as reliable indicators to whether a strategy survives. Stochasticity is added to investigate the effects of varying fractions of one strategy present at initialization time and to discuss the rich dynamic properties in greater detail. Finally, we derive Liapunov exponents for the system and show that chaos reigns in a small region where the two strategies coexist in dynamical equilibrium.