Effects of clipping and soil compaction on growth,morphology and mycorrhizal colonization of Schizachyrium scoparium,a C4 bunchgrass

Summary A factorial design of clipping and compaction was used to study the responses of Schizachyrium scoparium and its mycorrhizal symbionts to these stresses. All treatment combinations significantly reduced the growth and biomass of plants relative to controls. Compaction significantly reduced tillering and crown expansion while clipping increased tillering early in the growing season and reduced it later. Mycorrhizal colonization of roots was highest in the clipped plots and lowest in compacted plots. Spore number was highest in compacted plots and lowest in clipped plots. It appears that spore number may be negatively correlated with root growth since any treatment that reduced plant growth yielded higher spore numbers. The combination of clipping and compaction reduced plant growth the most, but had intermediate effects on mycorrhizal colonization and spore number.     

Phosphorylation of ezrin on threonine T567 plays a crucial role during compaction in the mouse early embryo

The preimplantation development of the mouse embryo leads to the divergence of the first two cell lineages, the inner cell mass and the trophectoderm. The formation of a microvillus pole during compaction at the eight-cell stage and its asymmetric inheritance during mitosis are key events in the emergence of these two cell populations. Ezrin, a member of the ERM protein family, seems to be involved in the formation and stabilization of this apical microvillus pole. To further characterize its function in early development, we mutated the key residue T567, which was reported to be essential for regulation of ezrin function through phosphorylation. Here, we show that expression of ezrin mutants in which the COOH-terminal threonine T567 was replaced by an aspartate (to mimic a phosphorylated residue; T567D) or by an alanine (to avoid phosphorylation; T567A) interferes with E-cadherin function and disrupts the first morphogenetic events of development: compaction and cavitation. The active mutant ezrin-T567D induces the formation of numerous and abnormally long microvilli at the surface of blastomeres. Moreover, it localizes all around the cell cortex and inhibits cell-cell adhesion and cell polarization at the eight-cell stage. During the following stages, only half of the embryos are able to compact and finally to cavitate. In those embryos, the amount of ezrin-T567D decreases in the basolateral areas, while the proportion of adherens junctions increases. The reverse inactive mutant ezrin-T567A is mainly cytoplasmic and does not perturb compaction at the eight-cell stage. However, at the 16-cell stage, it relocalizes at the basolateral cortex, leading to a strong decrease in the surface of adherens junctions, and finally, embryos abort development. Our results show that ezrin is directly involved in the formation of microvilli in the early mouse embryo. Moreover, they indicate that maintenance of ezrin in basolateral areas prevents microvilli breakdown and inhibits the formation of normal cell-cell contacts mediated by E-cadherin, thereby impairing blastomeres polarization and morphogenesis of the blastocyst.     

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.     

Tight junction biogenesis during early development

The tight junction (TJ) is an essential component of the differentiated epithelial cell required for polarised transport and intercellular integrity and signalling. Whilst much can be learnt about how the TJ is constructed and maintained and how it functions using a wide range of cellular systems, the mechanisms of TJ biogenesis within developmental models must be studied to gain insight into this process as an integral part of epithelial differentiation. Here, we review TJ biogenesis in the early mammalian embryo, mainly considering the mouse but also including the human and other species, and, briefly, within the amphibian embryo. We relate TJ biogenesis to inherent mechanisms of cell differentiation and biosynthesis occurring during cleavage of the egg and the formation of the first epithelium. We also evaluate a wide range of exogenous cues, including cell-cell interactions, protein kinase C signalling, gap junctional communication, Na⁺/K⁺-ATPase and cellular energy status, that may contribute to TJ biogenesis in the embryo and how these may shape the pattern of early morphogenesis.     

Surface histidine residue of archaeal histone affects DNA compaction and thermostability

Archaeal histone, which possesses only the core domain part of eukaryal histone, induced DNA compaction by binding to DNA. Based on structural modeling, tetramer formation by dimer-dimer interaction is considered to require two intermolecular ion pairs formed between histidine and aspartate. To examine the role of the ion pairs on DNA compaction, mutant histones were constructed and analyzed using HpkB from Thermococcus kodakaraensis KOD1 as a model protein. The mutant histones, HpkB-H50A, HpkB-H50V, and HpkB-H50G were constructed by replacing conserved surface His50 with Ala, Val, and Gly, respectively. Circular dichroism analysis indicated no significant difference between wild-type and mutants in their structures. Gel mobility shift assays showed that all mutants possessed DNA binding ability, like wild-type HpkB, however all mutants compacted DNA less efficiently than the wild-type. Moreover, all mutants could not maintain the nucleosome-like structure (compacted form of DNA) above 80 degrees C. These results suggest that surface ion pairs between His and Asp play an important role in maintenance of nucleosome structure and DNA stabilization at high temperature.     

Alkaline treatment has contrasting effects on the structure of deglycosylated and glycosylated forms of glucose oxidase

X-ray crystallographic studies on glucose oxidase showed a strong interaction between carbohydrate and protein moieties of the glycoprotein. However, experimental studies under physiological conditions reported no influence of carbohydrate moiety on the structural and functional properties of glucose oxidase. In order to demonstrate the role of carbohydrate moiety on the structure and stability, we carried out a detailed comparative study on the pH-induced structural changes in the native and deglycosylated forms of glucose oxidase. Our studies demonstrate that at physiological pH both forms of enzyme have very similar structural and stability properties. Acid denaturation also showed similar structural changes in both forms of the enzyme. However, on alkaline treatment contrasting effects on the structure and stability of the two forms of enzyme were observed. The glycosylated enzyme undergoes partial unfolding with decreased stability at alkaline pH; however, a compaction of native conformation and enhanced stability of enzyme was observed for the deglycosylated enzyme under similar conditions. This is the first experimental demonstration of the influence of carbohydrate moiety on structure and stability of glucose oxidase. The studies also indicate the importance of pH studies in evaluating the effect of carbohydrate moiety on the structural and stability properties of glycoprotein.     

Periostin promotes atrioventricular mesenchyme matrix invasion and remodeling mediated by integrin signaling through Rho/PI 3-kinase

Recent evidence suggests that extracellular matrix components may play a signaling role in embryonic valve development. We have previously identified the spatiotemporal expression patterns of periostin in developing valves, but its function during this process is largely unknown. To evaluate the functional role periostin plays during valvulogenesis, two separate three-dimensional culture assay systems, which model chick atrioventricular cushion development, were employed. These assays demonstrated that cushion mesenchymal cells adhered and spread on purified periostin in a dose-responsive manner, similar to collagen I and fibronectin via alpha(v)beta(3) and beta(1) integrin pairs. Periostin overexpression resulted in enhanced mesenchyme invasion through 3D collagen gels and increased matrix compaction. This invasion was dependent on alpha(v)beta(3) more than beta(1) integrin signaling, and was mediated differentially by Rho kinase and PI 3-kinase. Both matrix invasion and compaction were associated with a colocalization of periostin and beta(1) integrin expression to migratory cell phenotype in both surface and deep cells. The Rho/PI 3-kinase pathway also differentially mediated matrix compaction. Both Rho and PI 3-kinase were involved in normal cushion mesenchyme matrix compaction, but only PI 3-kinase was required for the enhanced matrix compaction due to periostin. Taken together, these results highlight periostin as a mediator of matrix remodeling by cushion mesenchyme towards a mature valve structure.     

Divalent cations cooperatively stabilize close membrane contacts in myelin

Intact nerve myelin compacts to a dehydrated structure of closely apposed membranes when exposed to isotonic solutions at least 10 mM in calcium or tetracaine. The repeat period of the membrane pair in the compacted structure measured by X-ray diffraction is about 126 Å in both central and peripheral mammalian nerve myelins whereas the normal periods are about 158 and 178 Å, respectively. The electron density profile of compacted myelin shows an asymmetric membrane unit with thickness similar to that of the symmetric bilayer of flocculated myelin lipids. The centrosymmetrically averaged myelin membrane profile is similar to that of the lipid bilayer except at the surface where residual protein is concentrated. Dispersions of extracted total myelin lipids flocculate under similar conditions to those causing myelin compaction, indicating that similar forces act in both processes. Compaction is always accompanied by lateral segregation of intramembrane particles out of the close-packed domains. Lateral displacement of intramembrane proteins from compacted domains can be driven by the attraction of the lipid surfaces for each other. Rates of compaction vary with compacting reagent, concentration, tissue, and temperature, and probably reflect the permeability of the tissue. Extensive compaction by calcium or tetracaine leads to disruption and vesiculation of the spirally wrapped myelin membranes.