Actin-based cellular framework for glucose signaling by Arabidopsis hexokinase1

Glucose functions in plants both as a metabolic resource as well as a hormone that regulates expression of many genes. Arabidopsis hexokinase1 (HXK1) is the best understood plant glucose sensor/transducer, yet we are only now appreciating the cellular complexity of its signaling functions. We have recently shown that one of the earliest detectable responses to plant glucose treatments are extensive alterations of cellular F-actin. Interestingly, AtHXK1 is predominantly located on mitochondria, yet also can interact with actin. A normal functioning actin cytoskeleton is required for HXK1 to act as an effector in glucose signaling assays. We have suggested that HXK1 might alter F-actin dynamics and thereby influence the formation and/or stabilization of cytoskeleton-bound polysomes. In this Addendum, we have extended our initial observations on the subcellular targeting of HXK1 and its interaction with F-actin. We then further consider the cellular context in which HXK1 might regulate gene expression.Key words: Arabidopsis, F-actin, glucose signaling, hexokinase, hTalin, mitochondria, polysomes, protoplasts, transient expression assay, fluorescence microscopy     

Effect of α-tocopherol supplementation during boar semen cryopreservation on sperm characteristics and expression of apoptosis related genes

Boar semen is extremely vulnerable to cold shock and sensitive to peroxidative damage due to high content of unsaturated fatty acids in the phospholipids of the plasma membrane and the relatively low antioxidant capacity of seminal plasma. The present study evaluated the influence of α-tocopherol supplementation at various concentrations in the boar semen extender during cryopreservation on post-thawed sperm motility characteristics (total sperm motility, MOT; local motility, LCM; curvilinear velocity, VCL; straight linear velocity, VSL; and average path velocity, VAP), sperm qualities (viability, acrosomal integrity and apoptosis), expression of stress protein (HSP70), and the expression of pro-apoptotic (Bax and Bak) and anti-apoptotic (Bcl-2l and Bcl-xl) genes. Semen collected from 10 Duroc boars was cryopreserved in lactose-egg yolk buffer supplemented with various concentrations of α-tocopherol (0, 100, 200, 400, 600 and 800 μM) using the straw-freezing procedure and stored at −196 °C for a minimum period of one month. In frozen-thawed groups, sperm motility was significantly (P < 0.05) lower than that of fresh sperm. In fresh sperm, HSP70 immunoreactivity expression was observed in the equatorial region, but in frozen-thawed groups, expressions were mostly observed in the sperm head. Higher apoptosis rates were observed in 600 and 800 μM α-tocopherol supplemented frozen-thawed groups. In α-tocopherol supplemented frozen-thawed groups immediately after thawing, the expression was similar to that of fresh group. But after incubation at 37 °C for 3 h, the expression in 200 and 800 μM α-tocopherol supplemented groups was higher than that of others. Expression of pro-apoptotic genes was significantly higher and anti-apoptotic genes was significantly (P < 0.01) lower in α-tocopherol supplemented frozen-thawed groups compared to fresh sperm group. In conclusion, α-tocopherol, supplemented at 200 μM concentration in boar semen extender during cryopreservation had a positive effect on post-thawed sperm survivability.     

Modulation of biocidal activity of <Emphasis Type="Italic">Calothrix</Emphasis> sp. and <Emphasis Type="Italic">Anabaena</Emphasis> sp. by environmental factors

An investigation was undertaken to evaluate a set of cyanobacterial strains in terms of production of biocidal compounds exhibiting allelochemical and fungicidal properties. Two cyanobacterial strains — Anabaena sp. and Calothrix sp. were selected for further investigation, on the basis of their larger inhibition zones on the lawn of Synechocystis and Synechococcus sp. and two phytopathogenic fungi — Rhizoctonia bataticola and Pythium debaryanum. The diameter of the inhibition zone was largest when extracellular filtrates of the two cultures incubated at high light intensity (90–100 μmol photons m⁻² s⁻¹) and temperature (40 ± 2 °C) or grown in medium containing two-folds higher P (1.4 mg/L, as compared to 0.7 mg/L in BG 11 medium) were taken. A pH of 8 was the most optimal for both strains, in terms of growth and biocidal activity. Partial purification of ethyl acetate extract using TLC, followed by GLC revealed a single peak. This study highlights the importance of environmental factors in aggravating or reducing the toxic effects of these harmful cyanobacteria and their potential as a biocontrol agent.     

Suicidal Membrane Repair Regulates Phosphatidylserine Externalization during Apoptosis

One of the hallmarks of apoptosis is the redistribution of phosphatidylserine (PS) from the inner-to-outer plasma membrane (PM) leaflet, where it functions as a ligand for phagocyte recognition and the suppression of inflammatory responses. The mechanism by which apoptotic cells externalize PS has been assumed to involve “scramblases” that randomize phospholipids across the PM bilayer. These putative activities, however, have not been unequivocally proven to be responsible for the redistribution of lipids. Because elevated cytosolic Ca²⁺ is critical to this process and is also required for activation of lysosome-PM fusion during membrane repair, we hypothesized that apoptosis could activate a “pseudo”-membrane repair response that results in the fusion of lysosomes with the PM. Using a membrane-specific probe that labels endosomes and lysosomes and fluorescein-labeled annexin 5 that labels PS, we show that the appearance of PS at the cell surface during apoptosis is dependent on the fusion of lysosomes with the PM, a process that is inhibited with the lysosomotrophe, chloroquine. We demonstrate that apoptotic cells evoke a persistent pseudo-membrane repair response that likely redistributes lysosomal-derived PS to the PM outer leaflet that leads to membrane expansion and the formation of apoptotic blebs. Our data suggest that inhibition of lysosome-PM fusion-dependent redistribution of PS that occurs as a result of chemotherapy- and radiotherapy-induced apoptosis will prevent PS-dependent anti-inflammatory responses that preclude the development of tumor- and patient-specific immune responses.There is increasing evidence that damaged plasma membranes (PM)² trigger an emergency Ca²⁺-dependent exocytotic repair response that patches the affected area by adding lysosome-derived membranes at the cell surface disruption site (1–5). Because high cytosolic Ca²⁺ concentrations trigger lysosome-PM fusion, the elevated cytosolic Ca²⁺ levels characteristic to apoptotic cells may also evoke a pseudo-repair mechanism that promotes lysosome-PM fusion. Indeed, similar to normal emergency repair responses, apoptosis is characterized by the appearance of organelle proteins and lipids at the PM surface (6–8). One critical distinction between the apoptotic and physiologic repair processes is the preservation of membrane lipid asymmetry. In normal cells, any perturbation in PS sidedness is corrected by restoration of basal cytosolic [Ca²⁺], reactivation of the Ca²⁺-inhibited aminophospholipid translocase (9, 10), and subsequent facilitated transport of PS back to the inner membrane leaflet of the cell. In apoptotic cells, however, persistent high cytosolic [Ca²⁺] precludes reactivation of the aminophospholipid translocase, and the redistributed PS remains in the outer membrane leaflet (11). The apparent similarities in these processes combined with observations that apoptotic cells express PS at the cell surface prompted us to investigate whether lysosome to PM fusion plays a role in the redistribution of PS during apoptosis.     

Understanding the molecular basis of plant growth promotional effect of Pseudomonas fluorescens on rice through protein profiling

Background  

Plant Growth Promoting Rhizobacteria (PGPR), Pseudomonas fluorescens strain KH-1 was found to exhibit plant growth promotional activity in rice under both in-vitro and in-vivo conditions. But the mechanism underlying such promotional activity of P. fluorescens is not yet understood clearly. In this study, efforts were made to elucidate the molecular responses of rice plants to P. fluorescens treatment through protein profiling. Two-dimensional polyacrylamide gel electrophoresis strategy was adopted to identify the PGPR responsive proteins and the differentially expressed proteins were analyzed by mass spectrometry.     

Sample size and statistical power considerations in high-dimensionality data settings: a comparative study of classification algorithms

Background  

Data generated using 'omics' technologies are characterized by high dimensionality, where the number of features measured per subject vastly exceeds the number of subjects in the study. In this paper, we consider issues relevant in the design of biomedical studies in which the goal is the discovery of a subset of features and an associated algorithm that can predict a binary outcome, such as disease status. We compare the performance of four commonly used classifiers (K-Nearest Neighbors, Prediction Analysis for Microarrays, Random Forests and Support Vector Machines) in high-dimensionality data settings. We evaluate the effects of varying levels of signal-to-noise ratio in the dataset, imbalance in class distribution and choice of metric for quantifying performance of the classifier. To guide study design, we present a summary of the key characteristics of 'omics' data profiled in several human or animal model experiments utilizing high-content mass spectrometry and multiplexed immunoassay based techniques.     

Fish venom (Pterios volitans) peptide reduces tumor burden and ameliorates oxidative stress in Ehrlich's ascites carcinoma xenografted mice

The present study was carried out to assess the effect of Pterios volitans venom (mixture of peptides) on Ehrlich’s ascites carcinoma (EAC) and its influence on antioxidant status in the liver. Among six groups of albino mice, three were treated with sublethal doses of venom, along with the standard drug, 5-fluorouracil. In EAC-bearing mice, mean life span and antioxidants were significantly decreased, whereas, body weight, tumor volume, viable tumor cell count, lipid peroxidation and expression of proliferating cell nuclear antigen were significantly increased. These changes were brought back to near normal in treatment groups. The findings are further confirmed by histopathological observations.     

How much the eye tells the brain

In the classic "What the frog's eye tells the frog's brain," Lettvin and colleagues showed that different types of retinal ganglion cell send specific kinds of information. For example, one type responds best to a dark, convex form moving centripetally (a fly). Here we consider a complementary question: how much information does the retina send and how is it apportioned among different cell types? Recording from guinea pig retina on a multi-electrode array and presenting various types of motion in natural scenes, we measured information rates for seven types of ganglion cell. Mean rates varied across cell types (6-13 bits . s(-1)) more than across stimuli. Sluggish cells transmitted information at lower rates than brisk cells, but because of trade-offs between noise and temporal correlation, all types had the same coding efficiency. Calculating the proportions of each cell type from receptive field size and coverage factor, we conclude (assuming independence) that the approximately 10(5) ganglion cells transmit on the order of 875,000 bits . s(-1). Because sluggish cells are equally efficient but more numerous, they account for most of the information. With approximately 10(6) ganglion cells, the human retina would transmit data at roughly the rate of an Ethernet connection.