MicroRNAs as mediators of insect host–pathogen interactions and immunity

Insects are the most successful group of animals on earth, owing this partly to their very effective immune responses to microbial invasion. These responses mainly include cellular and humoral responses as well as RNA interference (RNAi). Small non-coding RNAs (snRNAs) produced through RNAi are important molecules in the regulation of gene expression in almost all living organisms; contributing to important processes such as development, differentiation, immunity as well as host–microorganism interactions. The main snRNAs produced by the RNAi response include short interfering RNAs, microRNAs and piwi-interacting RNAs. In addition to the host snRNAs, some microorganisms encode snRNAs that affect the dynamics of host–pathogen interactions. In this review, we will discuss the latest developments in regards to the role of microRNA in insect host–pathogen interactions and provide some insights into this rapidly developing area of research.     

Campylobacter ureolyticus: an emerging gastrointestinal pathogen?

A total of 7194 faecal samples collected over a 1-year period from patients presenting with diarrhoea were screened for Campylobacter spp. using EntericBio(?) , a multiplex-PCR system. Of 349 Campylobacter-positive samples, 23.8% were shown to be Campylobacter ureolyticus, using a combination of 16S rRNA gene analysis and highly specific primers targeting the HSP60 gene of this organism. This is, to the best of our knowledge, the first report of C. ureolyticus in the faeces of patients presenting with gastroenteritis and may suggest a role for this organism as an emerging enteric pathogen.     

Angiotensin as a model for hormone — receptor interactions

Proton magnetic resonance and chemical reactivity studies have demonstrated the presence of a tyrosine charge relay system in angiotensin which is analogous to the serine charge relay system present at the active site of serine proteases. Receptor activation by angiotensin can be explained by electronic effects deriving from an interaction of the charge relay system with stacking of the histidine and phenylalanine rings. Experiments with serine protease inhibitors suggest the possibility that mechanistic features of the interaction of angiotensin with its receptors may apply to other phenoxyl hormones including certain peptides, steroids and catecholamines.     

Proteasomal degradation in plant–pathogen interactions

The ubiquitin/26S proteasome pathway is a basic biological mechanism involved in the regulation of a multitude of cellular processes. Increasing evidence indicates that plants utilize the ubiquitin/26S proteasome pathway in their immune response to pathogen invasion, emphasizing the role of this pathway during plant–pathogen interactions. The specific functions of proteasomal degradation in plant–pathogen interactions are diverse, and do not always benefit the host plant. Although in some cases, proteasomal degradation serves as an effective barrier to help plants ward off pathogens, in others, it is used by the pathogen to enhance the infection process. This review discusses the different roles of the ubiquitin/26S proteasome pathway during interactions of plants with pathogenic viruses, bacteria, and fungi.     

A nonlocal kinetic model for predator–prey interactions

We extend the aggregation model from Fetecau (2011) by adding a field of vision to individuals and by including a second species. The two species, assumed to have a predator–prey relationship, have dynamics governed by nonlocal kinetic equations that include advection and turning. The latter is the main mechanism for aggregation and orientation, which results from interactions among individuals of the same species as well as predator–prey relationships. We illustrate numerically a diverse set of predator–prey behaviors that can be captured by this model. We show that a prey’s escape outcome depends on the social interactions between its group members, the prey’s field of vision and the sophistication of the predator’s hunting strategies.     

Comparative analysis of Leishmania exoproteomes: Implication for host–pathogen interactions

Leishmaniasis is a vector-borne disease caused by the protozoa Leishmania. We have analyzed and compared the sequences of three experimental exoproteomes of Leishmania promastigotes from different species to determine their specific features and to identify new candidate proteins involved in interactions of Leishmania with the host. The exoproteomes differ from the proteomes by a decrease in the average molecular weight per protein, in disordered amino acid residues and in basic proteins. The exoproteome of the visceral species is significantly enriched in sites predicted to be phosphorylated as well as in features frequently associated with molecular interactions (intrinsic disorder, number of disordered binding regions per protein, interaction and/or trafficking motifs) compared to the other species. The visceral species might thus have a larger interaction repertoire with the host than the other species. Less than 10% of the exoproteomes contain heparin-binding and RGD sequences, and ~ 30% the host targeting signal RXLXE/D/Q. These latter proteins might thus be exported inside the host cell during the intracellular stage of the infection. Furthermore we have identified nine protein families conserved in the three exoproteomes with specific combinations of Pfam domains and selected eleven proteins containing at least three interaction and/or trafficking motifs including two splicing factors, phosphomannomutase, 2,3-bisphosphoglycerate-independent phosphoglycerate mutase, the paraflagellar rod protein-1D and a putative helicase. Their role in host–Leishmania interactions warrants further investigation but the putative ATP-dependent DEAD/H RNA helicase, which contains numerous interaction motifs, a host targeting signal and two disordered regions, is a very promising candidate.     

Chlorophyll fluorescence imaging of plant–pathogen interactions

Chlorophyll fluorescence imaging provides a noninvasive, non-destructive method with which to measure heterogenous changes in photosynthetic metabolism in plants infected by pathogens. The availability of commercial imaging fluorimeters has helped make this technique available to the wider scientific community, but considerable care is needed, both in experimental design and in the interpretation of results, to make the most of this powerful analytical tool. The origins of changes in chlorophyll fluorescence yield are discussed and the use of conventional and novel combinatorial imaging approaches explored, together with complementary techniques such as thermal imaging. This review examines the use of chlorophyll fluorescence imaging as a method for the early detection of viral, bacterial and fungal infection, before symptoms are visible by eye, and also as a means with which to probe underlying pathogen-induced changes in host physiology in both compatible and incompatible interactions. The use of chlorophyll fluorescence imaging to study host physiology is greatly enhanced when the atmosphere around the leaf is manipulated and simultaneous measurements of gas exchange made: The cost to the host plant of different resistance mechanisms can be calculated, the fate of the products of photosynthetic electron transport determined and localised alterations in the source–sink status of host tissue visualised.     

Host–pathogen interactions: a proteomic view

Host–pathogen interactions reflect the balance of host defenses and pathogen virulence mechanisms. Advances in proteomic technologies now afford opportunities to compare protein content between complex biologic systems ranging from cells to animals and clinical samples. Thus, it is now possible to characterize host–pathogen interactions from a global proteomic view. Most reports to date focus on cataloging protein content of pathogens and identifying virulence-associated proteins or proteomic alterations in host response. A more in-depth understanding of host–pathogen interactions has the potential to improve our mechanistic understanding of pathogenicity and virulence, thereby defining novel therapeutic and vaccine targets. In addition, proteomic characterization of the host response can provide pathogen-specific host biomarkers for rapid pathogen detection and characterization, as well as for early and specific detection of infectious diseases. A review of host–pathogen interactions focusing on proteomic analyses of both pathogen and host will be presented. Relevant genomic studies and host model systems will be also be discussed.     

Structural specificity in plant–filamentous pathogen interactions

Plant diseases bear names such as leaf blights, root rots, sheath blights, tuber scabs, and stem cankers, indicating that symptoms occur preferentially on specific parts of host plants. Accordingly, many plant pathogens are specialized to infect and cause disease in specific tissues and organs. Conversely, others are able to infect a range of tissues, albeit often disease symptoms fluctuate in different organs infected by the same pathogen. The structural specificity of a pathogen defines the degree to which it is reliant on a given tissue, organ, or host developmental stage. It is influenced by both the microbe and the host but the processes shaping it are not well established. Here we review the current status on structural specificity of plant–filamentous pathogen interactions and highlight important research questions. Notably, this review addresses how constitutive defence and induced immunity as well as virulence processes vary across plant organs, tissues, and even cells. A better understanding of the mechanisms underlying structural specificity will aid targeted approaches for plant health, for instance by considering the variation in the nature and the amplitude of defence responses across distinct plant organs and tissues when performing selective breeding.     

Comparative mapping of host–pathogen protein–protein interactions

1. Download : Download high-res image (177KB)
2. Download : Download full-size image

     

Hepatozoon silvestris: an emerging feline vector-borne pathogen in Europe?

Hepatozoon silvestris (Adeleorina: Hepatozoidae) is a recently described agent of feline hepatozoonosis. Although possibly emerging in Europe, this apicomplexan parasite is still largely unknown. Here, we provide insight into our current knowledge of the parasite’s distribution, biology, and pathogenesis of the associated disease.     

The roles of ABA in plant–pathogen interactions

Defence against abiotic and biotic stresses is crucial for the fitness and survival of plants under adverse or suboptimal growth conditions. The phytohormone abscisic acid (ABA) is not only important for mediating abiotic stress responses, but also plays a multifaceted and pivotal role in plant immunity. This review presents examples demonstrating the importance of crosstalk between ABA and the key biotic stress phytohormone salicylic acid in determining the outcome of plant–pathogen interactions. We then provide an overview of how ABA influences plant defence responses against various phytopathogens with particular emphasis on the Arabidopsis–Pseudomonas syringae model pathosystem. Lastly, we discuss future directions for studies of ABA in plant immunity with emphasis on, its role in the crosstalk between biotic and abiotic stress responses, the importance of distinguishing direct and indirect effects of ABA, as well as the prospect of utilizing the recently elucidated core ABA signaling network to gain further insights into the roles of ABA in plant immunity.     

Data mining for protein–protein interactions in invertebrate model organisms

Well-annotated genome databases are available for many invertebrate species, notably the fruitfly, Drosophila melanogaster, and the nematode, Caenorhabditis elegans. An adequate interpretation of this information at the biological level requires the exploration of the interactions between the gene products. Knowledge of protein interactions and the components of cell signalling pathways in the fly and worm are particularly valuable as hypotheses can be rapidly tested using the powerful genetic toolkits available. Invertebrates offer additional experimental advantages when attempting to characterise protein–protein interactions (PPIs). Their relatively small genome size compared to mammals helps to reduce missed interactions due to redundancy, and their function can be addressed using forward (mutants) and reverse (RNA interference) genetics. However, the researcher looking for evidence of PPIs for a protein of interest is faced with the challenge of extracting interaction data from sources that are highly varied, such as the results of microarray experiments in the unstructured text of research papers. This challenge is greatly reduced by a range of public databases of curated information, as well as publicly available, enhanced search engines, which can provide either direct experimental evidence for a PPI, or valuable clues for generating new hypotheses.     

β-Galactosidase-deficient mouse as an animal model for GM1-gangliosidosis

GM1-gangliosidosis is a progressive neurological disease in humans caused by deficiency of lysosomal acid β-galactosidase, which hydrolyses the terminal β-galactosidic residue from ganglioside GM1 and other glycoconjugates. In this study, we generated a mouse model for GM1-gangliosidosis by gene targeting in embryonic stem cells. The mouse homozygous for the disrupted β-galactosidase gene showed β-galactosidase deficiency, presented with progressive spastic diplegia, and died of emaciation at 7–10 months of age. Pathologically, PAS-positive intracytoplasmic storage was observed in neuronal cells of various areas in the brain. Biochemical analysis revealed a marked accumulation of ganglioside GM1 and asialo GM1 in brain tissue. This animal model will be useful for pathogenetic analysis and therapeutic trial of human GM1-gangliosidosis. This revised version was published online in November 2006 with corrections to the Cover Date.     

Helix-mediated protein–protein interactions as targets for intervention using foldamers

Protein–protein interactions (PPIs) play a central role in virtually all biological processes and have been the focus of intense investigation from structural molecular biology to cell biology for the majority of the last two decades and, more recently, are emerging as important targets for pharmaceutical intervention. A common motif found at the interface of PPIs is the α-helix, suggesting that, in the same way as the “lock and key” model has evolved for competitive inhibition of enzymes, it should be possible to elaborate “rule-based” approaches for inhibition of helix-mediated PPIs. This review will describe the biological function and structural features of a series of representative helix-mediated PPIs and discuss approaches that are being developed to target these interactions with small molecules that employ non-natural amino acids.