Changes in the Mark–Houwink hydrodynamic volume of chitosan molecules in solutions of different organic acids, at different temperatures and ionic strengths

The objective of this study is to explore the cause(s) of changes in the hydrodynamic volume of chitosan molecules in solutions of different organic acids, at different temperatures and ionic strengths. Change in intrinsic viscosity is used as the parameter to elucidate the causes of changes in the hydrodynamic volume of chitosan molecules in these solutions. Results show that the intrinsic viscosity of chitosan decreases in acetic acid or in malic acid over storage time. These decreases are more pronounced in acetic acid solution than in malic acid solution, more significant in higher temperature than in lower temperature solutions, and greater in solutions without NaCl than in solutions containing higher NaCl. The decrease in intrinsic viscosity can perhaps be attributed to the compounded effects of compaction of the chitosan molecules and/or acidic degradation during storage.     

Large gradient high magnetic field affects the association of MACF1 with actin and microtubule cytoskeleton

The intense inhomogeneous magnetic fields acting on the diamagnetic materials naturally present in cells can generate strong magnetic forces. We have developed a superconducting magnet platform with large gradient high magnetic field (LG‐HMF), which can produce three magnetic force fields of ?1360, 0, and 1312 T²/m, and three corresponding apparent gravity levels, namely 0, 1, and 2‐g for diamagnetic materials. In this study, the effects of different magnetic force fields on osteoblast‐like cells (MG‐63 and MC3T3‐E1) viability, microtubule actin crosslinking factor 1 (MACF1) expression and its association with cytoskeleton were investigated. Results showed that cell viability increased to different degrees after exposure to 0 or 1‐g conditions for 24 h, but it decreased by about 30% under 2‐g conditions compared with control conditions. An increase in MACF1 expression at the RNA or protein level was observed in osteoblast‐like cells under the magnetic force field of ?1360 T²/m (0‐g) relative to 1312 T²/m (2‐g). Under control conditions, anti‐MACF1 staining was scattered in the cytoplasm and partially colocalized with actin filaments (AFs) or microtubules (MTs) in the majority of osteoblast‐like cells. Under 0‐g conditions, MACF1 labeling was concentrated at perinuclear region and colocalization was not apparent. The patterns of anti‐MACF1 labeling on MTs varied with MTs' changing under LG‐HMF environment. In conclusion, LG‐HMF affects osteoblast‐like cell viability, MACF1 distribution, expression, and its association with cytoskeleton to some extent. Bioelectromagnetics 30:545–555, 2009. © 2009 Wiley‐Liss, Inc.     

Effects of exogenous B supply on growth, B accumulation and distribution of two navel orange cultivars

To investigate the effects of boron (B) on growth, B concentration and distribution of two navel orange cultivars, ‘Newhall’ (Citrus sinensis Osbeck) and ‘Skagg’s Bonanza’ (Citrus sinensis Osbeck) grafted on the rootstock trifoliate orange [Poncirus trifoliata (L.) Raf.], B at five levels was exogenously supplied to 1-year-old grafted plants of both cultivars under greenhouse conditions. Plants were grown in sand:perlite (1:1, v/v) medium and were irrigated every 2 days with half-strength Hoagland’s No. 2 nutrient solutions containing different B, 0.01, 0.05, 0.10, 0.25 and 2.50 mg l⁻¹ (0.25 and 2.50 mg l⁻¹ were considered as control and excess B treatment, respectively, and the other three B levels were considered as low B treatments). After treatments for 183 days, leaves (from basal, middle, upper parts of the shoots), stem of scion, stem of rootstock and root were separately sampled. Our results showed that plant growth (plant height, root volume and dry weights of various parts) was inhibited in response to low or excess B supplies in both cultivars. It was found that B concentrations in the upper leaves of both cultivars were substantially higher than those in the basal leaves when low concentrations (≤0.05 mg l⁻¹) of exogenous B were applied, suggesting that B was preferentially translocated to the upper-younger leaves to support their growth. Analysis of B distribution in different parts indicated that translocation of B from the root to the scion’s shoots (stems and leaves of scion) may be restricted upon exposure to low B conditions. When B was inadequately supplied, growth of ‘Skagg’s Bonanza’ was better than ‘Newhall’, implying that the former cultivar was more tolerant to low B status, which may be due to the higher efficiency of B translocation from the root to the scion’s shoots. However, when the plants were treated with excess B (2.50 mg l⁻¹), both cultivars showed a similar degree of B toxicity. The probability of scion–rootstock interactions in relation to the differential responses of growth and different efficiency of B translocation involved in the two orange cultivars following the long-term low B stress were discussed.     

Obesity and genetics regulate microRNAs in islets, liver, and adipose of diabetic mice

Type 2 diabetes results from severe insulin resistance coupled with a failure of β cells to compensate by secreting sufficient insulin. Multiple genetic loci are involved in the development of diabetes, although the effect of each gene on diabetes susceptibility is thought to be small. MicroRNAs (miRNAs) are noncoding 19–22-nucleotide RNA molecules that potentially regulate the expression of thousands of genes. To understand the relationship between miRNA regulation and obesity-induced diabetes, we quantitatively profiled approximately 220 miRNAs in pancreatic islets, adipose tissue, and liver from diabetes-resistant (B6) and diabetes-susceptible (BTBR) mice. More than half of the miRNAs profiled were expressed in all three tissues, with many miRNAs in each tissue showing significant changes in response to genetic obesity. Furthermore, several miRNAs in each tissue were differentially responsive to obesity in B6 versus BTBR mice, suggesting that they may be involved in the pathogenesis of diabetes. In liver there were approximately 40 miRNAs that were downregulated in response to obesity in B6 but not BTBR mice, indicating that genetic differences between the mouse strains play a critical role in miRNA regulation. In order to elucidate the genetic architecture of hepatic miRNA expression, we measured the expression of miRNAs in genetically obese F2 mice. Approximately 10% of the miRNAs measured showed significant linkage (miR-eQTLs), identifying loci that control miRNA abundance. Understanding the influence that obesity and genetics exert on the regulation of miRNA expression will reveal the role miRNAs play in the context of obesity-induced type 2 diabetes.     

Review of forest landscape models: Types, methods, development and applications

Forest landscape models simulate forest change through time using spatially referenced data across a broad spatial scale (i.e. landscape scale) generally larger than a single forest stand. Spatial interactions between forest stands are a key component of such models. These models can incorporate other spatio-temporal processes such as natural disturbances (e.g. wildfires, hurricanes, outbreaks of native and exotic invasive pests and diseases) and human influences (e.g. harvesting and commercial thinning, planting, fire suppression). The models are increasingly used as tools for studying forest management, ecological assessment, restoration planning, and climate change. In this paper, we define forest landscape models and discuss development, components, and types of the models. We also review commonly used methods and approaches of modeling forest landscapes, their application, and their strengths and weaknesses. New developments in computer sciences, geographic information systems (GIS), remote sensing technologies, decision-support systems, and geo-spatial statistics have provided opportunities for developing a new generation of forest landscape models that are increasingly valuable for ecological research, restoration planning and resource management.     

Kir5.1 underlies long-lived subconductance levels in heteromeric Kir4.1/Kir5.1 channels from Xenopus tropicalis

The inwardly-rectifying potassium channel subunit Kir5.1 selectively co-assembles with members of the Kir4.0 subfamily to form novel pH-sensitive heteromeric channels with unique single channel properties. In this study, we have cloned orthologs of Kir4.1 and Kir5.1 from the genome of the amphibian, Xenopus tropicalis (Xt). Heteromeric XtKir4.1/XtKir5.1 channels exhibit similar macroscopic current properties to rat Kir4.1/Kir5.1 with a faster time-dependent rate of activation. However, single channel analysis of heteromeric XtKir4.1/XtKir5.1 channels reveals that they have markedly different long-lived, multi-level subconductance states. Furthermore, we demonstrate that the XtKir5.1 subunit is responsible for these prominent subconductance levels. These results are consistent with a model in which the slow transitions between sublevel states represent the movement of individual subunits. These novel channels now provide an excellent model system to determine the structural basis of subconductance levels and contribution of heteromeric pore architecture to this process.     

Application of Fluorescence Spectroscopy to Quantify Shear-Induced Protein Conformation Change

Rapid and robust methods are required to quantify the effect of hydrodynamic shear on protein conformation change. We evaluated such strategies in this work and found that the binding of the fluorescent probe 4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonic acid (bis-ANS) to hydrophobic pockets in the blood protein von Willebrand factor (VWF) is enhanced upon the application of fluid shear to the isolated protein. Significant structural changes were observed when the protein was sheared at shear rates ≥ 6000/s for ∼3.5 min. The binding of bis-ANS to multimeric VWF, but not dimeric VWF or control protein bovine serum albumin, was enhanced upon fluid shear application. Thus, high-molecular-weight VWF is more susceptible to conformation change upon tensile loading. Although bis-ANS itself did not alter the conformation of VWF, it stabilized protein conformation once it bound the sheared molecule. Bis-ANS binding to VWF was reduced when the sheared protein was allowed to relax before dye addition. Taken together with functional data in the literature, our results suggest that shear-induced conformation changes in VWF reported by bis-ANS correlate well with the normal function of the protein under physiological/pathological fluid flow conditions. Further, this study introduces the fluorescent dye bis-ANS as a tool that may be useful in studies of shear-induced protein conformation change.     

cDNA microarray reveals the alterations of cytoskeleton-related genes in osteoblast under high magneto-gravitational environment

The diamagnetic levitation as a novel ground-based model for simulating a reduced gravity environment has been widely applied in many fields. In this study, a special designed superconducting magnet, which can produce three apparent gravity levels （0, 1, and 2 g）, namely high magneto-gravitational environment （HMGE）, was used to simulate space gravity environment. The effects of HMGE on osteoblast gene expression profile were investigated by microarray. Genes sensitive to diamagnetic levitation environment （0g）, gravity changes, and high magnetic field changes were sorted on the basis of typical cell func- tions. Cytoskeleton, as an intracellular load-bearing struc- ture, plays an important role in gravity perception. Therefore, 13 cytoskeleton-related genes were chosen according to the results of microarray analysis, and the expressions of these genes were found to be altered under HMGE by real-time PCR. Based on the PCR results, the expressions of WASF2 （WAS protein family, member 2）, WIPF1 （WAS/WASL interacting protein family, member 1）, paxillin, and talin 1 were further identified by western blot assay. Results indicated that WASF2 and WIPF1 were more sensitive to altered gravity levels, and talin 1 and paxillin were sensitive to both magnetic field and gravity changes. Our findings demonstrated that HMGE can affect osteoblast gene expression profile and cytoskele- ton-related genes expression. The identification of mechanosensitive genes may enhance our understandings to the mechanism of bone loss induced by microgravity and may provide some potential targets for preventing and treating bone loss or osteoporosis.     

Antitumor mechanism of Se-containing polysaccharide, a novel organic selenium compound

Recent studies on the inhibition of tumor growth by Se-containing polysaccharide were reviewed. Meanwhile, the possible molecular mechanisms of the inhibition of tumor cell growth through antioxidation, induction of tumor cell apoptosis, blockade of cell cycle, and enhancement of immunity by Se-containing polysaccharide were proposed. In the end, the potential application of Se-containing polysaccharide in the prevention and treatment of tumor was elucidated.