Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche

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Site-specific chlorophyll reference conditions for lakes in Northern and Western Europe

The Water Framework Directive (WFD) requires EU Member States to assess the “ecological status” of surface waters. As a component of ecological status, many European countries are developing a classification scheme for chlorophyll concentrations as a measure of phytoplankton biomass. The chlorophyll classification must be based on the degree of divergence of a water body from an appropriate baseline or ‘reference condition’. This article describes the development of a series of regression models for predicting reference chlorophyll concentrations on a site-specific basis. For model development, a large dataset of European lakes considered to be in reference condition, 466 lakes in total, was assembled. Data were included from 12 European countries, but lakes from Northern and Western Europe dominated and made up 92% of all reference lakes. Data have been collated on chlorophyll concentration, altitude, mean depth, alkalinity, humic type, surface area and geographical region. Regression models were developed for estimating site-specific reference chlorophyll concentrations from significant predictor ‘typology’ variables. Reference chlorophyll concentrations were found to vary along a number of environmental gradients. Concentrations increased with colour and alkalinity and decreased with lake depth and altitude. Forward selection was used to identify independent explanatory variables in regression models for predicting site-specific reference chlorophyll concentrations. Depth was selected as an explanatory variable in all models. Alkalinity was included in models for low colour and humic lakes and altitude was included in models for low colour and very humic lakes. Uncertainty in the models was quite high and arises from errors in the data used to develop the models (including natural temporal and spatial variability in data) and also from additional explanatory variables not considered in the models, particularly nutrient concentrations, retention time and grazing. Despite these uncertainties, site-specific reference conditions are still recommended in preference to type-specific reference conditions, as they use the individual characteristics of a site known to influence phytoplankton biomass, rather than adopt standards set to generally represent a large population of lakes of a particular type. For this reason, site-specific reference conditions should result in reduced error in ecological status classifications, particularly for lakes close to typology boundaries.     

Circular dichroism of the parallel β helical proteins pectate lyase C and E

The pectate lyases, PelC and PelE, have an unusual folding motif, known as a parallel β-helix, in which the polypeptide chain is coiled into a larger helix composed of three parallel β-sheets connected by loops having variable lengths and conformations. Since the regular secondary structure consists almost entirely of parallel β-sheets these proteins provide a unique opportunity to study the effect of parallel β-helical structure on circular dichroism (CD). We report here the CD spectra of PelC and PelE in the presence and absence of Ca²⁺, derive the parallel β-helical components of the spectra, and compare these results with previous CD studies of parallel β-sheet structure. The shape and intensity of the parallel β-sheet spectrum is distinctive and may be useful in identifying other proteins that contain the parallel β-helical folding motif. © 1995 Wiley-Liss, Inc.     

Molecular cut-off values of dialysis membranes for alginate and kappa-carrageenan oligosaccharides

The effective molecular weight cut-off values of dialysis membranes for carrageenan and alginate oligosaccharides were evaluated by gel permeation chromatography and nuclear magnetic resonance spectroscopy. For the different membranes tested, i.e. Medicell, Spectra Por 1000D and 3500D, the porous sizes are analogous to tri- and tetrasaccharides. A simple dialysis can be used to recover the majority of the oligosaccharides produced by a carrageenase or an alginate lyase digestion.     

The invertebrate fauna of High Arctic seabird nests: the microarthropod community inhabiting nests on Spitsbergen,Svalbard

The invertebrate fauna of the nests of three seabird species, black-legged kittiwakes (Rissa tridactyla), common eider (Somateria mollissima) and glaucous gull (Larus hyperboreus), were sampled in Kongsfjorden, Spitsbergen, Svalbard. The invertebrate community was species poor, consisting predominantly of the flea, Mioctenopsylla arctica arctica (Insecta: Siphonaptera), but with six species of oribatid mite (Acari: Oribatida), Diapterobates notatus, Oribatula tibialis, Ameronothrus lineatus, Hermannia reticulata, Trichoribates trimaculatus and Ceratoppia bipilis, plus an occasional mesostigmatid mite. No Collembola or ticks (Acari: Ixodidae) were observed. With the exception of M. arctica arctica, the fauna of seabird nests consisted of opportunistic microarthropod species rather than specialised nest-dwelling or bird parasitic species. Species diversity of soil oribatid mites was greater in nests of the common eider than compared to nests of the black-legged kittiwake, which may be related to the ground nesting behaviour of the common eiders. No rare or unusual microarthropod species for Svalbard were found in the seabird nests. The contentions that nests may facilitate microarthropod colonisation of High Arctic regions via bird phoresy by providing a high-quality habitat at the point of arrival, or that there might be a specialised microarthropod fauna exploiting this habitat, were not supported in this study. These are amongst the first data on the microarthropod community of seabird nests in the High Arctic.     

Genotype patterns and characteristics of PRNP in the Korean population

Creutzfeldt-Jakob disease (CJD), included in the human transmissible spongiform encephalopathies (TSE), is widely known to be caused by an abnormal accumulation of misfolding prion protein in the brain. Human prion protein gene (PRNP) is mapped in chromosome 20p13 and many single nucleotide polymorphisms (SNPs) in PRNP have been discovered. However, the functionality of SNPs in PRNP is yet unclear, though several SNPs have been known as important mutation related with susceptibility human prion diseases. Our aim is to identify specific genotype patterns and characteristics in the PRNP genomic region and to understand susceptibility among Korean discriminated prion disease patients, suspected CJD patients and the KARE data group. Here, we have researched genotypes and SNPs allele frequencies in PRNP in discriminated prion disease patients group (n = 22), suspected prion diseases patients group (n = 163) and the Korea Association REsource (KARE) data group (n = 296) in Korea. The sequencing regions were promoter region, exon1 and exon2 with their junction parts among 481 samples. A total of 25 SNPs were shown in this study. Nucleotide frequencies of all SNPs are exceedingly tended to bias toward dominant homozygote types except in rs2756271. Genotype frequencies at codon 129 and 219 coding region were similar with previous studies in Korea and Japan. Pathogenic mutations such as 102P/L, 200E/K and 203V/I were observed in discriminated CJD patients group, and 180V/I and 232M/R were shown in suspected prion disease patients group and the KARE data group. A total of 10 SNPs were newly identified, six in the promoter region, one in exon 2 and three in the 3′ UTR. The strong and unique linkage disequilibrium (D' = 0.94, r² = 0.89) was observed between rs57633656 and rs1800014 which is located in codon 219 coding region. We expect that these data can be provided to determine specific susceptibility and a protective factor of prion diseases not only in Koreans but also in East Asians.     

Heterotypic Humoral and Cellular Immune Responses following Norwalk Virus Infection

Norovirus immunity is poorly understood as the limited data available on protection after infection are often contradictory. In contrast to the more prominent GII noroviruses, GI norovirus infections are less frequent in outbreaks. The GI noroviruses display very complex patterns of heterotypic immune responses following infection, and many individuals are highly susceptible to reinfection. To study the immune responses and mechanisms of GI.1 persistence, we built structural models and recombinant virus-like particles (VLPs) of five GI strains: GI.1-1968, GI.1-2001, GI.2-1999, GI.3-1999, and GI.4-2000. Structural models of four GI genotype capsid P domain dimers suggested that intragenotype structural variation is limited, that the GI binding pocket is mostly preserved between genotypes, and that a conserved, surface-exposed epitope may allow for highly cross-reactive immune responses. GI VLPs bound to histo-blood group antigens (HBGAs) including fucose, Lewis, and A antigens. Volunteers infected with GI.1-1968 (n = 10) had significant increases between prechallenge and convalescent reactive IgG for all five GI VLPs measured by enzyme immunoassay. Potential cross-neutralization of GI VLPs was demonstrated by convalescent-phase serum cross-blockade of GI VLP-HBGA interaction. Although group responses were significant for all GI VLPs, each individual volunteer demonstrated a unique VLP blockade pattern. Further, peripheral blood mononuclear cells (PBMCs) were stimulated with each of the VLPs, and secretion of gamma interferon (IFN-γ) was measured. As seen with blockade responses, IFN-γ secretion responses differed by individual. Sixty percent responded to at least one GI VLP, with only two volunteers responding to GI.1 VLP. Importantly, four of five individuals with sufficient PBMCs for cross-reactivity studies responded more robustly to other GI VLPs. These data suggest that preexposure history and deceptive imprinting may complicate PBMC and B-cell immune responses in some GI.1-1968-challenged individuals and highlight a potential complication in the design of efficacious norovirus vaccines.Noroviruses are the second-most important cause of severe viral gastroenteritis in young children and cause approximately 20% of endemic familial diarrheal disease and traveler''s diarrhea in all ages (reviewed in references 45 and 70). Noroviruses are genetically grouped into five different genogroups (GI to GV). GI and GII genogroups are responsible for the majority of human infections and are subdivided into more than 25 different genotypes (for example, GI.1 is genogroup I genotype 1). Most norovirus outbreaks are caused by the GII.4 genotype (65). Although genogroup I strains are associated with fewer reported outbreaks, they are frequently identified in environmental samples and in children (7, 21, 33, 58, 74, 82). The severity of norovirus disease is usually moderate although infection can be especially virulent, even fatal, in the elderly (14, 24, 31, 38, 46, 67). An effective vaccine would be particularly advantageous to vulnerable older populations, food handlers, child and health care providers, and military personnel. One major obstacle to norovirus vaccine development is the lack of understanding of the extensive antigenic relationships between heterogenic norovirus family members and of how this antigenic heterogeneity affects host protective immunity. Norovirus heterogeneity can be examined through sequence, structural, ligand binding, and host immune studies.Structurally, noroviruses are ∼38-nm icosahedral viruses with an ∼7.5 kb single-stranded, positive-sense RNA genome that encodes three large open reading frames (ORFs). ORF1 encodes the replicase polyprotein, while ORFs 2 and 3 encode the major and minor capsid proteins, respectively. The ORF2 major capsid protein sequence can vary by up to 60% between genogroups and by ∼20 to 30% between the genotypes (91). Expression of the major capsid protein (ORF2) in baculovirus and Venezuelan equine encephalitis (VEE) results in formation of virus-like particles (VLPs) composed of 180 copies of the monomeric protein (72). The monomer is structurally divided into the shell domain (S) that forms the structural core of the particle and the protruding domain (P) that protrudes away from the core. The P domain is further subdivided into the P1 subdomain (residues 226 to 278 and 406 to 520) and the P2 subdomain (residues 279 to 405) (72). P2 represents the most exposed surface of the viral particle and determines interaction with both potential neutralizing antibody recognition sites and putative cellular receptors, the histo-blood group antigens (HBGAs) (13, 16, 54, 57).The P domain has been shown to independently form dimers and P particles comprised of 12 monomers (85). Dimers and P particles share structural and HBGA binding similarities with the VLP generated with the same monomers (9, 85, 87). Three norovirus-HBGA binding profiles have been identified: (i) those that bind A/B and/or H epitopes, (ii) those that bind Lewis and/or H epitopes, and (iii) those that do not bind any available HBGA (86). Elegant structural analyses of Norwalk virus VLPs in complex with synthetic HBGAs identified a highly conserved binding site within the G1 noroviruses and predicted that structural constraints within the GI strains would restrict HBGA binding patterns to either a terminal Gal-Fuc or GalNAc (18, 88).Norwalk virus (NV; GI.1-1968) is the prototypic GI strain and typically infects individuals who encode a functional FUT2 α-1,2-fucosyltransferase enzyme resulting in expression of HBGAs on mucosal surfaces (secretor-positive phenotype) (53). Individuals who do not encode a functional FUT2 enzyme have a secretor-negative phenotype, do not express ABH HBGAs on mucosal surfaces, and are resistant to NV infection. Outbreak investigations have confirmed the association between HBGA expression and norovirus infection for some GI and GII strains (37, 39, 43, 49, 89). It remains likely that enzymes other than FUT2 may function as norovirus susceptibility factors because secretor-negative individuals have low-level norovirus-reactive antibodies (49, 52, 53) and can become infected after challenge with a GII.2 strain (52); in addition, some norovirus strains bind to FUT2-independent HBGAs in vitro (35, 54, 79).Early challenge studies (reviewed in reference 50) suggested that short-term protective immunity may occur following NV challenge (96). Demonstration of long-term protective immunity has been more complex. One early rechallenge study found that 50% of NV-challenged volunteers experienced repeat infections after ∼3 years while the other 50% remained well initially and after repeated challenge (69). Whether these volunteers remained disease free because of acquired immunity or genetic resistance could not be ascertained (69). However, contemporary norovirus challenge studies suggest that an early mucosal IgA response is associated with protection from NV infection (53). Further, strong gamma interferon (IFN-γ) secretion from CD4⁺ T cells (52) was identified in some uninfected GII.2-1976-challenged volunteers.In the absence of additional rechallenge studies, the most compelling evidence for a long-term protective immune response comes from the growing number of reports from around the world indicating that periods of “high norovirus activity” correlated with the emergence of new GII.4 strains (1, 10, 42, 66, 75, 90). Subsequently, the years following the high activity were characterized by decreased numbers of outbreaks, indicating that herd immunity may be an important regulator of GII.4 noroviruses (54, 80, 81). Clearly, the molecular basis for differential protective immunity/susceptibility following repeat norovirus infection is complex and a major challenge for the field.In this report, we compare the VLP phenotypes of the prototypical norovirus strain NV to an extant GI.1 strain isolated 33 years after NV and to a panel of VLPs representing strains GI.2, GI.3, and GI.4. In the results, we evaluate sequence conservation, carbohydrate (CHO) binding patterns, and antigenic relatedness at the antibody and T-cell levels. In contrast to earlier predictions (19), these data suggest that the GI noroviruses can bind many different HBGAs and that individuals infected with norovirus usually mount robust B- and T-cell responses against homologous strains. Surprisingly, some individuals appear to preferentially mount immune responses against heterologous GI strains.     

Recent advances in ecological stoichiometry: insights for population and community ecology

Conventional theories of population and community dynamics are based on a single currency such as number of individuals, biomass, carbon or energy. However, organisms are constructed of multiple elements and often require them (in particular carbon, phosphorus and nitrogen) in different ratios than provided by their resources; this mismatch may constrain the net transfer of energy and elements through trophic levels. Ecological stoichiometry, the study of the balance of elements in ecological processes, offers a framework for exploring ecological effects of such constraints. We review recent theoretical and empirical studies that have considered how stoichiometry may affect population and community dynamics. These studies show that stoichiometric constraints can affect several properties of populations (e.g. stability, oscillations, consumer extinction) and communities (e.g. coexistence of competitors, competitive interactions between different guilds). We highlight gaps in general knowledge and focus on areas of population and community ecology where incorporation of stoichiometric constraints may be particularly fruitful, such as studies of demographic bottlenecks, spatial processes, and multi-species interactions. Finally, we suggest promising directions for new research by recommending potential study systems (terrestrial insects, detritivory-based webs, soil communities) to improve our understanding of populations and communities. Our conclusion is that a better integration of stoichiometric principles and other theoretical approaches in ecology may allow for a richer understanding of both population and community structure and dynamics.     

Multiannual effects of induced plant defenses: Are defended plants good or bad neighbors?

Defenses induced by herbivore feeding or phytohormones such as methyl jasmonate (MeJA) can affect growth, reproduction, and herbivory, not only on the affected individual but also in its neighboring plants. Here, we report multiannual defense, growth, and reproductive responses of MeJA‐treated bilberry (Vaccinium myrtillus) and neighboring ramets. In a boreal forest in western Norway, we treated bilberry ramets with MeJA and water (control) and measured responses over three consecutive years. We observed the treatment effects on variables associated with herbivory, growth, and reproduction in the MeJA‐treated and untreated ramet and neighboring ramets distanced from 10 to 500 cm. MeJA‐treated ramets had fewer grazed leaves and browsed shoots compared to control, with higher effects in 2014 and 2015, respectively. In 2013, growth of control ramets was greater than MeJA‐treated ramets. However, MeJA‐treated ramets had more flowers and berries than control ramets 2 years after the treatment. The level of insect and mammalian herbivory was also lower in untreated neighboring ramets distanced 10–150 cm and, consistent with responses of MeJA‐treated ramets, the stronger effect was also one and 2 years delayed, respectively. The same neighboring ramets had fewer flowers and berries than untreated ramets, indicating a trade‐off between defense and reproduction. Although plant–plant effects were observed across all years, the strength varied by the distance between the MeJA‐treated ramets and its untreated neighbors. We document that induced defense in bilberry reduces both insect and mammalian herbivory, as well as growth, over multiple seasons. The defense responses occurred in a delayed manner with strongest effects one and 2 years after the induction. Additionally, our results indicate defense signaling between MeJA‐treated ramets and untreated neighbors. In summary, this study shows that induced defenses are important ecological strategies not only for the induced individual plant but also for neighboring plants across multiple years in boreal forests.