Friend or foe? The role of leaf-inhabiting fungal pathogens and endophytes in tree-insect interactions

Trees are large organisms that structure forest ecosystems by providing an environment for an enormous diversity of animal, microbial and plant species. As these species use trees as their common hosts, many are likely to interact with each other directly or indirectly. From studies on herbaceous plant species we know that microbes can affect the interaction of plants with herbivorous insects, for example via changes in plant metabolite profiles. The consequences of fungal colonization for tree-insect interactions are, however, barely known, despite the importance of these ecological communities. In this review we explore the interaction of leaf-inhabiting pathogenic and endophytic fungi with trees and the consequences for tree-living insect herbivores. We discuss molecular, physiological, chemical, biochemical and ecological aspects of tree-fungus interactions and summarize the current knowledge on the direct and indirect effects of tree-inhabiting fungi on insect herbivores.Our mechanistic understanding of the tripartite interaction of trees with leaf-inhabiting fungi and insect herbivores is still in its infancy. We are currently facing substantial drawbacks in experimental methodology that prevent us from revealing the effect of one single fungal species on a particular insect herbivore species and vice versa. Future studies applying a versatile toolbox of modern molecular, chemical analytical and ecological techniques in combined laboratory and field experiments will unequivocally lead to a better understanding of fungus-tree-insect interactions.     

Selfish or selfless? The role of empathy in economics

Empathy is a longstanding issue in economics, especially for welfare economics, but one which has faded from the scene in recent years. However, with the rise of neuroeconomics, there is now a renewed interest in this subject. Some economists have even gone so far as to suggest that neuroscientific experiments reveal heterogeneous empathy levels across individuals. If this were the case, this would be in line with economists'' usual assumption of stable and given preferences and would greatly facilitate the study of prosocial behaviour with which empathy is often associated. After reviewing some neuroscientific psychological and neuroeconomic evidence on empathy, we will, however, criticize the notion of a given empathy distribution in the population by referring to recent experiments on a public goods game that suggest that, on the contrary, the degree of empathy that individuals exhibit is very much dependent on context and social interaction.     

The role of stratifin in fibroblast–keratinocyte interaction

Stratifin is a member of 14-3-3 protein family, a highly conserved group of proteins constituted by seven isoforms. They are involved in numerous crucial intracellular functions such as cell cycle and apoptosis, regulation of signal transduction pathways, cellular trafficking, cell proliferation and differentiation, cell survival, and protein folding and processing, among others. At epidermal level, stratifin (also called 14-3-3 sigma) has been described as molecule with relevant functions. For instance, this isoform is a marker associated with keratinocyte differentiation. In this maturation process, the presence of dominant negative molecules of p53 induces a “stemness condition” of keratinocyte precursor cells and suppression of stratifin expression. In addition, the recently described keratinocyte-releasable form of stratifin is involved in dermal fibroblast MMP-1 over-expression through c-Fos and c-Jun activity. This effect is mediated, at least in part, by p38 mitogen-activated protein kinase (MAPK). Other MMP family members such as stromelysin-1 (MMP-3), stromelysin-2 (MMP-10), neutrophil collagenase (MMP-8), and membrane-type MMP-24 (MT5-MMP) are also up-regulated by stratifin. Within fibroproliferative disorder of skin, hypertrophic scar and keloids exhibit a high content of collagen, proteoglycans, and fibronectin. Thus, the MMP profile induced by stratifin is an interesting starting point to establish new therapeutic tools to control the process of wound healing. In this review, we will focus on site of synthesis and mode of action of stratifin in skin and wound healing.     

The role of corridors in conservation: Solution or bandwagon?

Corridors are currently a major buzzword in conservation biology and landscape ecology. These linear landscape features may perform numerous functions, but it is their role in facilitating movement of fauna that has attracted much recent debate. The database supporting the idea of corridors acting as faunal conduits is remarkably small, and few studies have actually demonstrated that movement along corridors is important for any given species. Such data are very difficult to obtain, and conservation biologists are thus faced with the problem of whether to recommend the allocation of resources to corridors on the assumption that they may be important.     

The role of VDAC in cell death: Friend or foe?

As the voltage-dependent anion channel (VDAC) forms the interface between mitochondria and the cytosol, its importance in metabolism is well understood. However, research on VDAC's role in cell death is a rapidly growing field, unfortunately with much confusing and contradictory results. The fact that VDAC plays a role in outer mitochondrial membrane permeabilization is undeniable, however, the mechanisms behind this remain very poorly understood. In this review, we will summarize the studies that show evidence of VDAC playing a role in cell death. To begin, we will discuss the evidence for and against VDAC's involvement in mitochondrial permeability transition (MPT) and attempt to clarify that VDAC is not an essential component of the MPT pore (MPTP). Next, we will evaluate the remaining literature on VDAC in cell death which can be divided into three models: proapoptotic agents escaping through VDAC, VDAC homo- or hetero-oligomerization, or VDAC closure resulting in outer mitochondrial membrane permeabilization through an unknown pathway. We will then discuss the growing list of modulators of VDAC activity that have been associated with induction/protection against cell death. This article is part of a Special Issue entitled: VDAC structure, function, and regulation of mitochondrial metabolism.     

The role of sleep in declarative memory consolidation: passive,permissive, active or none?

Those inclined to relish in scientific controversy will not be disappointed by the literature on the effects of sleep on memory. Opinions abound. Yet refinements in the experimental study of these complex processes of sleep and memory are bringing this fascinating relationship into sharper focus. A longstanding position contends that sleep passively protects memories by temporarily sheltering them from interference, thus providing precious little benefit for memory. But recent evidence is unmasking a more substantial and long-lasting benefit of sleep for declarative memories. Although the precise causal mechanisms within sleep that result in memory consolidation remain elusive, recent evidence leads us to conclude that unique neurobiological processes within sleep actively enhance declarative memories.     

The physiological role of GLP-1 in human: incretin, ileal brake or more?

The proglucagon-derived peptide glucagon-like peptide-1 (GLP-1) is an intestinal signal peptide postprandially released from the L cells of the lower gut. Exogenously administered the synthetic hormone exerts a glucose-dependent insulinotropic effect at the pancreatic beta-cells and lowers plasma glucagon by an inhibitory effect against the alpha-cells. It delays gastric emptying by relaxation of the gastric fundus, inhibition of antral contractility, and stimulation of both the tonic and phasic motility of the pyloric sphincter. Enhancement of insulin, suppression of glucagon, and inhibition of gastric emptying are the main determinants controlling glucose homeostasis with GLP-1. Human studies employing the specific GLP-1 receptor antagonist exendin(9-39) show that endogenously released GLP-1 likewise controls fasting plasma glucagon, stimulates insulin, and influences all the motoric mechanisms known to control gastric emptying. Therefore, GLP-1 is discussed as an incretin hormone and as an enterogastrone in man. Synthetic GLP-1 also suppresses gastric acid and pancreatic enzyme secretion. The inhibitory effects on upper gastrointestinal functions are at least partly mediated by vagal-cholinergic inhibition and may involve interactions with vagal afferent pathways and/or circumventricular regions within the CNS. GLP-1 is a candidate humoral mediator of the 'ileal brake' exerting inhibition of upper gastrointestinal function preventing malabsorption and postprandial metabolic disturbances. As human studies indicate a central action of GLP-1 in reduction of food intake, it is uncertain if this is a consequence of induction of satiety or of transduction of visceral aversive stress signals.     

The role of habitat in avian community composition: physiognomy or floristics?

Summary It has been proposed that within rather broad habitat types the distribution and abundance of bird species may be more closely associated with plant taxonomic composition than with the structure and configuration of the vegetation. Birds from a sample of eight representative grassland habitats in middle and western North America are consistent with this hypothesis. Over half (55%) of the variation in bird community composition was associated with floristic variation, but only a third (35%) was associated with physiognomy. Separating the interacting effects of floristics and physiognomy from each other served to accentuate the difference between them with respect to the avifauna. It is postulated that bird species/plant taxa associations, especially within similar habitat types, are mediated by the specific food resources that different plant taxa provide. Summary indices such as diversity measures obscure the taxonomic information content of plant or animal assemblages, and the use of such indices has likely impeded detection of the relationships described here.     

The role of phytic acid in legumes: antinutrient or beneficial function?

This review describes the present state of knowledge about phytic acid (phytate), which is often present in legume seeds. The antinutritional effects of phytic acid primarily relate to the strong chelating associated with its six reactive phosphate groups. Its ability to complex with proteins and particularly with minerals has been a subject of investigation from chemical and nutritional viewpoints. The hydrolysis of phytate into inositol and phosphates or phosphoric acid occurs as a result of phytase or nonenzymatic cleavage. Enzymes capable of hydrolysing phytates are widely distributed in micro-organisms, plants and animals. Phytases act in a stepwise manner to catalyse the hydrolysis of phytic acid. To reduce or eliminate the chelating ability of phytate, dephosphorylation of hexa- and penta-phosphate forms is essential since a high degree of phosphorylation is necessary to bind minerals. There are several methods of decreasing the inhibitory effect of phytic acid on mineral absorption (cooking, germination, fermentation, soaking, autolysis). Nevertheless, inositol hexaphosphate is receiving increased attention owing to its role in cancer prevention and/or therapy and its hypocholesterolaemic effect.     

The role of oxidative stress in anxiety disorder: cause or consequence?

Anxiety disorders are the most common mental illness in the USA affecting 18% of the population. The cause(s) of anxiety disorders is/are not completely clear, and research in the neurobiology of anxiety at the molecular level is still rather limited. Although mounting clinical and preclinical evidence now indicates that oxidative stress may be a major component of anxiety pathology, whether oxidative stress is the cause or consequence remains elusive. Studies conducted over the past few years suggest that anxiety disorders may be characterised by lowered antioxidant defences and increased oxidative damage to proteins, lipids, and nucleic acids. In particular, oxidative modifications to proteins have actually been proposed as a potential factor in the onset and progression of several psychiatric disorders, including anxiety and depressive disorders. Oxidised proteins are normally degraded by the proteasome proteolytic complex in the cell cytoplasm, nucleus, and endoplasmic reticulum. The Lon protease performs a similar protective function inside mitochondria. Impairment of the proteasome and/or the Lon protease results in the accumulation of toxic oxidised proteins in the brain, which can cause severe neuronal trauma. Recent evidence points to possible proteolytic dysfunction and accumulation of damaged, oxidised proteins as factors that may determine the appearance and severity of psychotic symptoms in mood disorders. Thus, critical interactions between oxidative stress, proteasome, and the Lon protease may provide keys to the molecular mechanisms involved in emotional regulation, and may also be of great help in designing and screening novel anxiolytics and antidepressants.     

Recycling or regulation? The role of amino-terminal modifying enzymes

Post-translational modifications are essential for a variety of functions, such as the translocation, activation, regulation, and, ultimately, degradation of proteins. The amino-terminal (N-terminal) region is a particularly active area for such alterations. Three types of reactions predominate: limited proteolysis to remove one or more amino acids; modification of the alpha-amino group; and side-chain-specific changes. The N-terminal peptidases expose penultimate residues, providing new substrates for peptidase or transferase action. These enzymes can act sequentially or competitively to influence a protein's longevity, location or activity. N-terminal modifying enzymes (NTMEs) might target a protein for ubiquitination and degradation or protect a protein from rapid turnover. The N-terminal peptidases might also have important roles in processing the peptides that are released from the proteasome. Plant NTMEs have roles in senescence, meiosis and defense, and proposed roles in polar auxin transport.     

The GITR-GITRL interaction: co-stimulation or contrasuppression of regulatory activity?

Stimulation of T cells through GITR (glucocorticoid-induced tumour-necrosis-factor-receptor-related protein) has been shown to enhance immunity to tumours and viral pathogens, and to exacerbate autoimmune disease. The effects of stimulation through GITR are generally thought to be caused by attenuation of the effector activity of immunosuppressive CD4+ CD25+ regulatory T (T(Reg)) cells. Here we propose a model in which GITR-GITR-ligand interactions co-stimulate both responder T-cell functions and the suppressive functions of T(Reg) cells.     

The role of sphingosine kinase 1 in cancer: oncogene or non-oncogene addiction?

Sphingosine kinase 1 (SphK1) is a lipid kinase that catalyses the phosphorylation of sphingosine to sphingosine-1-phosphate. There is strong evidence from cellular or animal systems that SphK1 is involved in the major mechanisms underpinning oncogenesis, namely, the promotion of cellular survival, proliferation and transformation, the prevention of apoptosis and the stimulation of angiogenesis. Furthermore there is also good evidence from clinical samples that SphK1 is overexpressed in many, if not most tumor types examined and that many inhibitors of SphK1 render tumors sensitive to chemotherapeutic agents. A major question that remains concerns the exact mechanism of action of SphK1 in cancer. The tools available to probe SphK1 function perturb a set of cellular functions, and it is possible that several of these are involved in driving its oncogenic role. Furthermore, the importance of SphK1 functions in normal physiology and the lack of mutations of SphK1 in cancer, suggest that the mechanism in cancer might be an over reliance on this system of cellular signaling; an example of non-oncogene addiction.     

The role of ecotourism in conservation: panacea or Pandora’s box?

Does ecotourism contribute towards conservation of threatened species and habitats or is it just a marketing ploy of the tourism industry? Using 251 case studies on ecotourism from the literature, I looked at the distribution of case studies over continents, habitats and flagship species types and what factors influenced whether an ecotourism regime was perceived as ecologically sustainable by authors. Over 50% of ecotourism case studies were reported from Africa and Central America. The overall distribution of ecotourism case studies did not reflect vertebrate endemism, nor overall tourism distribution in terms of tourist numbers and receipts. There were significant differences between continents and habitats with regard to the proportion of sustainable case studies: ecotourism is perceived to be less sustainable in South America and Asia, and in island and mountain habitats. The type of flagship species also influenced whether ecotourism was classified as sustainable or not: ecotourism with no flagship species was rarely classified as sustainable while charismatic bird and mammal species were associated with a higher probability of sustainability. In a multivariate analysis, flagship species type and local community involvement were important predictors of sustainability in ecotourism. Detailed a priori planning, local involvement and control measures were perceived by authors of case studies to increase the success of ecotourism in conservation. They also perceived that ecotourism can only be an effective conservation tool under certain conditions. If these are met, the evidence indicates that ecotourism can make a contribution to conservation.     

Iron in infectious diseases friend or foe?: The role of gut microbiota

Iron is a trace element involved in metabolic functions for all organisms, from microorganisms to mammalians. Iron deficiency is a prevalent health problem that affects billions of people worldwide, and iron overload could have some hazardous effect. The complex microbial community in the human body, also called microbiota, influences the host immune defence against infections. An imbalance in gut microbiota, dysbiosis, changes the host's susceptibility to infections by regulating the immune system. In recent years, the number of studies on the relationship between infectious diseases and microbiota has increased. Gut microbiota is affected by different parameters, including mode of delivery, hygiene habits, diet, drugs, and plasma iron levels during the lifetime. Gut microbiota may influence iron levels in the body, and iron overload and deficiency can also affect gut microbiota composition. Novel researches on microbiota shed light on the fact that the bidirectional interactions between gut microbiota and iron play a role in the pathogenesis of many diseases, especially infections. A better understanding of these interactions may help us to comprehend the pathogenesis of many infectious and metabolic diseases affecting people worldwide and following the development of more effective preventive and/or therapeutic strategies. In this review, we aimed to present the iron-mediated host-gut microbiota interactions, susceptibility to bacterial infections, and iron-targeted therapy approaches for infections.     

The role of the anticodon in the interaction between methionyl-tRNA synthetase and bacterial initiator tRNA?

Complementary and antiparallel oligonucleotides bind to exposed regions of the tRNA molecule. Aminoacylation in the presence of triplets has been used to determine the role of the anticodon in the interaction between methionyl-tRNA synthetase and initiator tRNA. ApUpG has no effect on the charging even when 70% of the tRNA is bound to the triplet, whereas in the presence of GpGpU which binds to the A-C-C sequence adjacent to the 3' terminal adenosine that fraction of the tRNA which is bound to the triplet is completely unavailable for charging. Hence the anticodon is probably not involved in a primary interaction while the A-C-C-A-OH clearly is. This conclusion is supported by the failure of the isolated anticodon loop and stem oligonucleotides to inhibit the aminoacylation reaction.     

The role of floods in the lives of fish-eating birds: predator loss or benefit?

Floods accompanied by high flow and high water turbidity are usually believed to cause problems to fish-eating birds and mammals searching visually for their prey. In the present study the diets of breeding kingfishers were studied during the normal river situation and during a long-lasting flood event with respect to diet composition, size of fish prey and food diversity index. During the normal situation (flow 1.75 m³ s^?1, Secchi disc depth 0.5–1 m), the diet of a kingfisher was dominated by benthic fish species (52.9% by numbers, 63.9% by weight), the average size of fish taken was 6.5 cm L _T and 3.0 g and the food diversity index reached its lowest value (1.57). In contrast, during the long-lasting flood event (flow 5–28 m³ s^?1, Secchi disc depth 0.03–0.4 m) the diet of the kingfisher was dominated by sub-surface fish species (72.4% by numbers, 76.1% by weight) and both the average size of fish taken (7.4 cm L _T and 3.7 g) and the food diversity index (1.83) increased significantly. The birds provided their nestlings with lower numbers of fish of larger sizes, which resulted in very similar weights of the young birds prior to fledging when the flood and normal situations were compared. This study provides evidence that in different foraging conditions the kingfishers adopt different foraging strategies to maintain their high breeding success.