Plant fructan exohydrolases: a role in signaling and defense?

Fructans are fructose oligomers and polymers synthesized by a small number of plant and bacterial species and mainly function as reserve carbohydrates. The terminal fructosyl-fructose linkages can be degraded by fructan exohydrolases (FEHs), occurring in bacteria, fungi and fructan plants. Unexpectedly, it was found that FEHs also occur in non-fructan plants such as Beta vulgaris and Arabidopsis thaliana that apparently lack endogenous fructan substrates. FEHs might have defense-related roles acting on bacterial fructan-containing slimes or might act on minute (up to now undetected) amounts of fructans acting as signals in plants.     

Photoentrainment in mammals: a role for cryptochrome?

There is growing evidence in support of the hypothesis that, in mammals, photoreceptive tasks are segregated into those associated with creating a detailed visual image of the environment and those involved in the photic regulation of temporal biology. The hypothesis that this segregation extends to the use of different photoreceptors remains unproven, but published reports from several mammalian species that circadian photoentrainment survives a degree of retinal degeneration sufficient to induce visual blindness suggest that this may be so. This has lead to speculation that mammals might employ a dedicated 'circadian photoreceptor' distinct from the rod and cone cells of the visual system. The location and nature of this putative circadian photoreceptor has become a matter of conjecture. The latest candidates to be put forward as potential circadian photopigments are the mammalian cryptochrome proteins (CRY1 and 2), putative vitamin-B2 based photopigments. To date, published experimental evidence falls short of a definitive demonstration that these proteins form the basis of circadian photoreception in mammals. Consequently, this review aims to assess their suitability for this task in light of what we know regarding the biology of the cyrptochromes and the nature of mammalian photoentrainment.     

Lipoproteins and mitogen-activated protein kinase signaling: a role in atherogenesis?

PURPOSE OF REVIEW: Lipoproteins play a critical role in the development of atherosclerosis, which might result partly from their capacity to induce specific intracellular signaling pathways. The goal of this review is to summarize the signaling properties of lipoproteins, in particular, their capacity to induce activation of mitogen-activated protein kinase pathways and the resulting modulation of cellular responses in blood vessel cells. RECENT FINDINGS: Lipoproteins activate the extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways in all blood vessel cell types. This may require lipoprotein docking to scavenger receptor B1, allowing transfer of cholesterol and sphingosine-1-phosphate to plasma membranes. Subsequent propagation of the signals probably requires the stimulation of G protein-coupled receptors, followed by the transactivation of receptor tyrosine kinases. Lipoprotein-induced extracellular signal-regulated kinase activity favors cell proliferation, whereas lipoprotein-induced p38 mitogen-activated protein kinase activity leads to cell hyperplasia and promotes cell migration. Some signaling pathways and cellular effects induced by lipoproteins have been observed in atherosclerotic plaques and therefore represent potential targets for the development of anti-atherosclerotic drugs. SUMMARY: The main blood vessel cell types have the capacity to activate protein kinase pathways in the presence of lipoproteins. This induces cell proliferation, hyperplasia and migration, known to be dysregulated in atherosclerotic lesions.     

Trypanosomiasis and trypanotolerance in cattle: a role for congopain?

A Trypanosoma congolense cysteine protease (congopain) elicits a high IgG response in trypanotolerant but not in trypanosusceptible cattle during primary infections. As discussed here by Edith Authié, this observation suggests that congopain, like other parasite cysteine proteases, may play a role in pathogenicity and that more efficient immune responses to congopain may contribute to trypanotolerance.     

Metabolic alterations triggered by silicon nutrition: Is there a signaling role for silicon?

Although the beneficial role of silicon (Si) in stimulating the growth and development of many plants is generally accepted, our knowledge concerning the physiological and molecular mechanisms underlying this response remains far from comprehensive. Considerable effort has been invested in understanding the role of Si on plant disease, which has led to several new and compelling hypotheses; in unstressed plants, however, Si is believed to have no molecular or metabolic effects. Recently, we have demonstrated that Si nutrition can modulate the carbon/nitrogen balance in unstressed rice plants. Our findings point to an important role of Si as a signaling metabolite able to promote amino acid remobilization. In this article we additionally discuss the agronomic significance of these novel observations and suggest Si nutrition as an important target in future attempts to improve yields of agronomic crops.     

Cortical maps: a role for astrocytes?

Astrocytes are a multifunctional cell type in the nervous system that can influence neurons and synapses in numerous ways. Astrocytes have been suggested to play important roles in synapse formation during development, as well as in multiple forms of synaptic plasticity in the developing and adult brain. Astrocytes respond to nearby neural activity with elevations in cytosolic calcium concentration, and in sensory cortex these calcium responses have been shown to be topographically aligned to neuronal sensory maps. Here, we review recent evidence for astrocyte interactions with neural circuits, with particular emphasis on how these interactions may shape the development, arrangement and plasticity of cortical sensory maps.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

Hybrid speciation in sparrows II: a role for sex chromosomes?

Homoploid hybrid speciation in animals is poorly understood, mainly because of the scarcity of well‐documented cases. Here, we present the results of a multilocus sequence analysis on the house sparrow (Passer domesticus), Spanish sparrow (P. hispaniolensis) and their proposed hybrid descendant, the Italian sparrow (P. italiae). The Italian sparrow is shown to be genetically intermediate between the house sparrow and Spanish sparrow, exhibiting genealogical discordance and a mosaic pattern of alleles derived from either of the putative parental species. The average variation on the Z chromosome was significantly reduced compared with autosomal variation in the putative parental species, the house sparrow and Spanish sparrow. Additionally, divergence between the two species was elevated on the Z chromosome relative to the autosomes. This pattern of variation and divergence is consistent with reduced introgression of Z‐linked genes and/or a faster‐Z effect (increased rate of adaptive divergence on the Z). F_ST‐outlier tests were consistent with the faster‐Z hypothesis: two of five Z‐linked loci (CHD1Z and PLAA) were identified as candidates for being subject to positive, divergent selection in the putative parental species. Interestingly, the two latter genes showed a mosaic pattern in the (hybrid) Italian sparrow; that is, the Italian sparrow was found to be fixed for Spanish sparrow alleles at CHD1Z and to mainly have house sparrow alleles at PLAA. Preliminary evidence presented in this study thus suggests that sex chromosomes may play a significant role in this case of homoploid hybrid speciation.     

Hybridization and speciation in angiosperms: a role for pollinator shifts?

The majority of convincingly documented cases of hybridization in angiosperms has involved genetic introgression between the parental species or formation of a hybrid species with increased ploidy; however, homoploid (diploid) hybridization may be just as common. Recent studies, including one in BMC Evolutionary Biology, show that pollinator shifts can play a role in both mechanisms of hybrid speciation.     

Neurotoxic species in prion disease: a role for PrP isoforms?

Prion diseases such as bovine spongiform encephalopathy in cattle and Creutzfeldt–Jakob disease in humans are associated with the misfolding and accumulation of an abnormal conformation of the host-encoded prion protein (PrP). Despite intensive research efforts conducted on PrP, the toxic agent involved in neurodegeneration is as yet unidentified. Several potential candidates have been proposed, each of which may be relevant to subsets of the broad array of prion diseases. In this study, we review current knowledge on neurotoxic PrP species, including the importance of a central hydrophobic domain for mediating neurotoxicty.     

Trace fear conditioning: a role for context?

Fear conditioning can be rapidly obtained over long trace intervals, but its specificity with respect to both time and stimulus is uncertain. Long-trace fear conditioning often parallels contextual conditioning, and it is sensitive to hippocampal lesions. These properties of trace conditioning are not directly addressed by timing models and multiple-time-scale models of conditioning. It is proposed that during early stages of conditioning, a joint representation of the context and the stimulus trace may underlie conditioned responses, and that discriminative processes allow the emergence of specific responses in a later stage.