Aquaporin gating

An acceleration in the rate at which new aquaporin structures are determined means that structural models are now available for mammalian AQP0, AQP1, AQP2 and AQP4, bacterial GlpF, AqpM and AQPZ, and the plant SoPIP2;1. With an apparent consensus emerging concerning the mechanism of selective water transport and proton extrusion, emphasis has shifted towards the issues of substrate selectivity and the mechanisms of aquaporin regulation. In particular, recently determined structures of plant SoPIP2;1, sheep and bovine AQP0, and Escherichia coli AQPZ provide new insights into the underlying structural mechanisms by which water transport rates are regulated in diverse organisms. From these results, two distinct pictures of 'capping' and 'pinching' have emerged to describe aquaporin gating.     

The chloroplast lumen and stromal proteomes of Arabidopsis thaliana show differential sensitivity to short- and long-term exposure to low temperature

Cold acclimation and over-wintering by herbaceous plants are energetically expensive and are dependent on functional plastid metabolism. To understand how the stroma and the lumen proteomes adapt to low temperatures, we have taken a proteomic approach (difference gel electrophoresis) to identify proteins that changed in abundance in Arabidopsis chloroplasts during cold shock (1 day), and short- (10 days) and long-term (40 days) acclimation to 5 degrees C. We show that cold shock (1 day) results in minimal change in the plastid proteomes, while short-term (10 days) acclimation results in major changes in the stromal but few changes in the lumen proteome. Long-term acclimation (40 days) results in modulation of the proteomes of both compartments, with new proteins appearing in the lumen and further modulations in protein abundance occurring in the stroma. We identify 43 differentially displayed proteins that participate in photosynthesis, other plastid metabolic functions, hormone biosynthesis and stress sensing and signal transduction. These findings not only provide new insights into the cold response and acclimation of Arabidopsis, but also demonstrate the importance of studying changes in protein abundance within the relevant cellular compartment.     

Stevioside does not cause increased basal insulin secretion or beta-cell desensitization as does the sulphonylurea, glibenclamide: studies in vitro

We have shown that stevioside (SVS) enhances insulin secretion and thus may have a potential role as antihyperglycemic agent in the treatment of type 2 diabetes mellitus. However, whether SVS stimulates basal insulin secretion (BIS) and/or cause desensitization of beta cells like sulphonylureas (SU), e.g. glibenclamide (GB), is not known. To explore and compare the effects of SVS pretreatment with those of GB and glucagon-like peptide-1 (GLP-1), we exposed isolated mouse islets to low or high glucose for 1 h after short-term (2 h) or long-term (24 h) pretreatment with SVS, GB or GLP-1, respectively. BIS at 3.3 or 5.5 mM glucose were not changed after short-term pretreatment with SVS (10(-7) M), while it increased about three folds after pretreatment with GB (10(-7) M). Glucose stimulated insulin secretion (GSIS) (16.7 mM) increased dose-dependently after long-term pretreatment with SVS at concentrations from 10(-7) to 10(-5) M. Pretreatment for 24 h with GB (10(-7) M) increased the subsequent BIS (3.3 mM glucose) (p < 0.001), but decreased GSIS (16.7 mM glucose) (p < 0.001). In contrast SVS (10(-7) M) and GLP-1 (10(-7) M) did not stimulate BIS but both enhanced the subsequent GSIS (16.7 mM glucose) (p < 0.05 and p < 0.05, respectively). While SVS pretreatment increased the intracellular insulin content, GB pretreatment decreased the insulin content. Our study suggests that SVS pretreatment does not cause a stimulation of BIS and does not desensitize beta-cells, i.e. SVS seems to have advantageous characteristics to GB as a potential treatment of type 2 diabetes.     

Neurotransmitter synthesis in poststroke cortical neurogenesis in adult rats

Neurogenesis occurs in the cerebral cortex of adult rats after focal cerebral ischemia. Whether or not the newborn neurons could synthesize neurotransmitters is unknown. To elucidate such a possibility, a photothrombotic ring stroke model with spontaneous reperfusion was induced in adult male Wistar rats. The DNA duplication marker BrdU was repeatedly injected, and the rats were sacrificed at various times after stroke. To detect BrdU nuclear incorporation and various neurotransmitters, brain sections were processed for single/double immunocytochemistry and single/double/triple immunofluorescence. Stereological cell counting was performed to assess the final cell populations. At 48 h, 5 days, 7 days, 30 days, 60 days and 90 days after stroke, numerous cells were BrdU-immunolabeled in the penumbral cortex. Some of these were doubly immunopositive to the cholinergic neuron-specific marker ChAT or GABAergic neuron-specific marker GAD. As analyzed by 3-D confocal microscopy, the neurotransmitters acetylcholine and GABA were colocalized with BrdU in the same cortical cells. In addition, GABA was colocalized with the neuron-specific marker Neu N in the BrdU triple-immunolabeled cortical cells. This study suggests that the newborn neurons are capable of synthesizing the neurotransmitters acetylcholine and GABA in the penumbral cortex, which is one of the fundamental requisites for these neurons to function in the poststroke recovery.     

Fibrillation of the major curli subunit CsgA under a wide range of conditions implies a robust design of aggregation

The amyloid fold is usually considered a result of protein misfolding. However, a number of studies have recently shown that the amyloid structure is also used in nature for functional purposes. CsgA is the major subunit of Escherichia coli curli, one of the most well-characterized functional amyloids. Here we show, using a highly efficient approach to prepare monomeric CsgA, that in vitro fibrillation of CsgA occurs under a wide variety of environmental conditions and that the resulting fibrils exhibit similar structural features. This highlights how fibrillation is "hardwired" into amyloid that has evolved for structural purposes in a fluctuating extracellular environment and represents a clear contrast to disease-related amyloid formation. Furthermore, we show that CsgA polymerization in vitro is preceded by the formation of thin needlelike protofibrils followed by aggregation of the amyloid fibrils.     

Real-time detection of central carbon metabolism in living Escherichia coli and its response to perturbations

The direct tracking of cellular reactions in vivo has been facilitated with recent technologies that strongly enhance NMR signals in substrates of interest. This methodology can be used to assay intracellular reactions that occur within seconds to few minutes, as the NMR signal enhancement typically fades on this time scale. Here, we show that the enhancement of (13)C nuclear spin polarization in deuterated glucose allows to directly follow the flux of glucose signal through rather extended reaction networks of central carbon metabolism in living Escherichia coli. Alterations in central carbon metabolism depending on the growth phase or upon chemical perturbations are visualized with minimal data processing by instantaneous observation of cellular reactions.     

OpenCMISS: A multi-physics & multi-scale computational infrastructure for the VPH/Physiome project

The VPH/Physiome Project is developing the model encoding standards CellML (cellml.org) and FieldML (fieldml.org) as well as web-accessible model repositories based on these standards (models.physiome.org). Freely available open source computational modelling software is also being developed to solve the partial differential equations described by the models and to visualise results. The OpenCMISS code (opencmiss.org), described here, has been developed by the authors over the last six years to replace the CMISS code that has supported a number of organ system Physiome projects.OpenCMISS is designed to encompass multiple sets of physical equations and to link subcellular and tissue-level biophysical processes into organ-level processes. In the Heart Physiome project, for example, the large deformation mechanics of the myocardial wall need to be coupled to both ventricular flow and embedded coronary flow, and the reaction-diffusion equations that govern the propagation of electrical waves through myocardial tissue need to be coupled with equations that describe the ion channel currents that flow through the cardiac cell membranes.In this paper we discuss the design principles and distributed memory architecture behind the OpenCMISS code. We also discuss the design of the interfaces that link the sets of physical equations across common boundaries (such as fluid-structure coupling), or between spatial fields over the same domain (such as coupled electromechanics), and the concepts behind CellML and FieldML that are embodied in the OpenCMISS data structures. We show how all of these provide a flexible infrastructure for combining models developed across the VPH/Physiome community.     

Paired opposing leukocyte receptors recognizing rapidly evolving ligands are subject to homogenization of their ligand binding domains

Some leukocyte receptors come in groups of two or more where the partners share ligand(s) but transmit opposite signals. Some of the ligands, such as MHC class I, are fast evolving, raising the problem of how paired opposing receptors manage to change in step with respect to ligand binding properties and at the same time conserve opposite signaling functions. An example is the KLRC (NKG2) family, where opposing variants have been conserved in both rodents and primates. Phylogenetic analyses of the KLRC receptors within and between the two orders show that the opposing partners have been subject to post-speciation gene homogenization restricted mainly to the parts of the genes that encode the ligand binding domains. Concerted evolution similarly restricted is demonstrated also for the KLRI, KLRB (NKR-P1), KLRA (Ly49), and PIR receptor families. We propose the term merohomogenization for this phenomenon and discuss its significance for the evolution of immune receptors.     

Domestication effects on behavioural synchronization and individual distances in chickens (Gallus gallus)

Behavioural synchrony (allelomimetic behaviour), and inter-individual distances are aspects of social and anti-predator strategies which may have been affected by domestication. Chickens are known to adjust synchronization and inter-individual distances depending on behaviour. We hypothesized that White Leghorn (WL) chickens would show less synchronized behaviour than the ancestor, the red jungle fowl (RJF). Sixty birds, 15 female and 15 male WL and the same number of RJF (28 weeks old) were studied in groups of three in furnished pens (1 m × 2 m) for 24 consecutive hours per group, following 24 h of habituation. Video tapes covering 4 h per group (dawn, 9-10 am, 1-2 pm and dusk) were analysed. Red junglefowl perched significantly more, but there were no breed effects on the frequency or daily rhythm of any other activities, or on average inter-individual distances. Red junglefowl were more synchronized during perching and a tendency for the same was found for social behaviour. After performance of the two most synchronized behaviours, perching and comfort behaviour, individual distance increased more for RJF than WL. According to this study domestication of chickens appears not to have significantly altered the relative frequencies of different activities or average inter-individual distances, but have caused some changes in behavioural synchronization and maintenance of activity-specific inter-individual distances in chickens. The changes may indicate an adaptive response to captivity and domestication.