Vinculin, cadherin mechanotransduction and homeostasis of cell–cell junctions

Cell adhesion junctions characteristically arise from the cooperative integration of adhesion receptors, cell signalling pathways and the cytoskeleton. This is exemplified by cell–cell interactions mediated by classical cadherin adhesion receptors. These junctions are sites where cadherin adhesion systems functionally couple to the dynamic actin cytoskeleton, a process that entails physical interactions with many actin regulators and regulation by cell signalling pathways. Such integration implies a potential role for molecules that may stand at the interface between adhesion, signalling and the cytoskeleton. One such candidate is the cortical scaffolding protein, vinculin, which is a component of both cell–cell and cell–matrix adhesions. While its contribution to integrin-based adhesions has been extensively studied, less is known about how vinculin contributes to cell–cell adhesions. A major recent advance has come with the realisation that cadherin adhesions are active mechanical structures, where cadherin serves as part of a mechanotransduction pathway by which junctions sense and elicit cellular responses to mechanical stimuli. Vinculin has emerged as an important element in cadherin mechanotransduction, a perspective that illuminates its role in cell–cell interactions. We now review its role as a cortical scaffold and its role in cadherin mechanotransduction.     

Genome Sequence of Multidrug-Resistant Escherichia coli EC302/04, Isolated from a Human Tracheal Aspirate

Escherichia coli is an important etiologic agent of lower respiratory tract infections (LRTI). Multidrug-resistant E. coli EC302/04 was isolated from a tracheal aspirate, and its genome sequence is expected to provide insights into antimicrobial resistance as well as adaptive and virulence mechanisms of E. coli involved in LRTI.     

Some aspects of the fine structure of the alimentary tract of the infective larva of Breinlia sergenti (Nematoda: Filarioidea).

The fine structure of the alimentary tract of the infective larva of Breinlia sergenti has been studied. The possible derivation of the oesophagus from the pharyngeal thread of the microfilaria is discussed.     

Prostaglandin E2 production by rat peritoneal macrophages: role of cellular and humoral factors in vivo in transfusion-associated immunosuppression

Abstract The transfusion of blood is associated with long-term immunosuppression, which has been postulated to influence immunosurveillance and cancer cell killing. The mononuclear phagocyte synthesises large quantities of PGE₂, and PGE₂ has been shown to inhibit the activity of a range of immunocompetent cell types. The role of mononuclear phagocyte PGE₂ synthesis in transfusion-associated immunosuppression, and the elements of transfused blood which control this immunosuppression, were investigated using a transfused rat model. A significant increase in macrophage PGE₂ synthesis was detected 7 days after transfusion with blood and serum. The storage of blood for 24 h increased the stimulatory activity of transfused blood. The effects of storage and serum on macrophage PGE₂ synthesis were greater than effects due to genetic differences between blood donor and recipient, and the serum effects indicated that a major factor activating PGE₂-mediated immunosuppression in transfused subjects may be humoral in nature.     

Effects of irradiance and spectral quality on seedling development of two Southeast Asian Hopea species

 Seedling developmental responses to understory shade combine the effects of reductions in irradiance and changes in spectral quality. We studied the seedling development of two Southeast Asian dipterocarp trees in response to differences in irradiance (photosynthetic photon flux density, PPFD) and spectral quality (red to far-red ratio, R:FR). The two species, Hopea helferei and H. odorata, are taxonomically closely related but differ in their ecological requirements; H. helferei is more drought-tolerant and typically grows in more open habitats. Seedlings were grown in six different replicated shadehouse treatments varying in percentage of solar PPFD and R:FR. The two species differed in the influence of light variables on most seedling characters, particularly for final height, internode distance, branch/trunk internodes, stem length/mass, leaf area/stem length, petiole length, and growth/mol of photons received. Most of the characters in both taxa were primarily influenced by PPFD, but spectral quality also influenced some characters – more so for H. odorata. The latter species grew more rapidly, particularly in the low PPFD treatments, and its leaves were capable of higher photosynthesis rates. However, growth in H. helferei was not reduced in direct sunlight. The growth of this taxon may be constrained by adaptations, particularly in leaves, for drought tolerance. Received: 14 April 1996 / Accepted: 8 October 1996     

Simulated beetle defoliation on willow genotypes in mixture and monotype plantations

The effect of simulated beetle damage (0%, 25%, 50% and 75% mechanical defoliation) on 12 willow genotypes, grown in short‐rotation coppice, was studied in a modified criss‐cross experimental design. The design enabled the above‐ground effects of monoculture and mixed planting to be assessed. Repeated measurements were modelled to produce derived variables in terms of time or, more appropriately, in terms of accumulated day length (i.e. ‘developmental time’) units. These derived variables were then analysed using the REsidual Maximum Likelihood (REML) method implemented in GenStat? (2001) . No significant competition effect between the genotypes due to planting regime was detected. Genotypes Salix viminalis × Salix schwerinii‘Beagle’ and S. viminalis × S. schwerinii‘Torhild’ were found to have the greatest rate of increase in leaves regardless of defoliation and also the greatest height prior to defoliation. Genotype Salix dasyclados‘Loden’ showed the highest rate of growth under the stress of defoliation. When assessing height at the end of the growing season, S. viminalis × S. schwerinii‘Olof’ was the highest genotype for 25% and 75% levels of defoliation, but genotypes Salix aurita × Salix cinerea‘Delamere’, Loden and S. viminalis × Salix burjatica‘Ashton Parfitt’ appeared to be most tolerant by having consecutively lower base day lengths (i.e. increasing the accumulation of developmental units and the length of the growing season) for increasing defoliation. Shorter genotypes tended to be more tolerant, but of the higher genotypes reaching a control height of greater than 3 m by the end of the growing season, S. viminalis × S. schwerinii‘Tora’ and Beagle performed best to 50% defoliation.     

Long-Term Evolution of the Hypervariable Region of Hepatitis C Virus in a Common-Source-Infected Cohort

The long-term evolution of the hepatitis C virus hypervariable region (HVR) and flanking regions of the E1 and E2 envelope proteins have been studied in a cohort of women infected from a common source of anti-D immunoglobulin. Whereas virus sequences in the infectious source were relatively homogeneous, distinct HVR variants were observed in each anti-D recipient, indicating that this region can evolve in multiple directions from the same point. Where HVR variants with dissimilar sequences were present in a single individual, the frequency of synonymous substitution in the flanking regions suggested that the lineages diverged more than a decade previously. Even where a single major HVR variant was present in an infected individual, this lineage was usually several years old. Multiple lineages can therefore coexist during long periods of chronic infection without replacement. The characteristics of amino acid substitution in the HVR were not consistent with the random accumulation of mutations and imply that amino acid replacement in the HVR was strongly constrained. Another variable region of E2 centered on codon 60 shows similar constraints, while HVR2 was relatively unconstrained. Several of these features are difficult to explain if a neutralizing immune response against the HVR is the only selective force operating on E2. The impact of PCR artifacts such as nucleotide misincorporation and the shuffling of dissimilar templates is discussed.     

Remodeling the zonula adherens in response to tension and the role of afadin in this response

Morphogenesis requires dynamic coordination between cell–cell adhesion and the cytoskeleton to allow cells to change shape and move without losing tissue integrity. We used genetic tools and superresolution microscopy in a simple model epithelial cell line to define how the molecular architecture of cell–cell zonula adherens (ZA) is modified in response to elevated contractility, and how these cells maintain tissue integrity. We previously found that depleting zonula occludens 1 (ZO-1) family proteins in MDCK cells induces a highly organized contractile actomyosin array at the ZA. We find that ZO knockdown elevates contractility via a Shroom3/Rho-associated, coiled-coil containing protein kinase (ROCK) pathway. Our data suggest that each bicellular border is an independent contractile unit, with actin cables anchored end-on to cadherin complexes at tricellular junctions. Cells respond to elevated contractility by increasing junctional afadin. Although ZO/afadin knockdown did not prevent contractile array assembly, it dramatically altered cell shape and barrier function in response to elevated contractility. We propose that afadin acts as a robust protein scaffold that maintains ZA architecture at tricellular junctions.     

Ribosome hibernation factor promotes Staphylococcal survival and differentially represses translation

In opportunistic Gram-positive Staphylococcus aureus, a small protein called hibernation-promoting factor (HPF_Sa) is sufficient to dimerize 2.5-MDa 70S ribosomes into a translationally inactive 100S complex. Although the 100S dimer is observed in only the stationary phase in Gram-negative gammaproteobacteria, it is ubiquitous throughout all growth phases in S. aureus. The biological significance of the 100S ribosome is poorly understood. Here, we reveal an important role of HPF_Sa in preserving ribosome integrity and poising cells for translational restart, a process that has significant clinical implications for relapsed staphylococcal infections. We found that the hpf null strain is severely impaired in long-term viability concomitant with a dramatic loss of intact ribosomes. Genome-wide ribosome profiling shows that eliminating HPF_Sa drastically increased ribosome occupancy at the 5′ end of specific mRNAs under nutrient-limited conditions, suggesting that HPF_Sa may suppress translation initiation. The protective function of HPF_Sa on ribosomes resides at the N-terminal conserved basic residues and the extended C-terminal segment, which are critical for dimerization and ribosome binding, respectively. These data provide significant insight into the functional consequences of 100S ribosome loss for protein synthesis and stress adaptation.