Evidence that αC region is origin of low modulus, high extensibility, and strain stiffening in fibrin fibers

Fibrin fibers form the structural scaffold of blood clots and perform the mechanical task of stemming blood flow. Several decades of investigation of fibrin fiber networks using macroscopic techniques have revealed remarkable mechanical properties. More recently, the microscopic origins of fibrin's mechanics have been probed through direct measurements on single fibrin fibers and individual fibrinogen molecules. Using a nanomanipulation system, we investigated the mechanical properties of individual fibrin fibers. The fibers were stretched with the atomic force microscope, and stress-versus-strain data was collected for fibers formed with and without ligation by the activated transglutaminase factor XIII (FXIIIa). We observed that ligation with FXIIIa nearly doubled the stiffness of the fibers. The stress-versus-strain behavior indicates that fibrin fibers exhibit properties similar to other elastomeric biopolymers. We propose a mechanical model that fits our observed force extension data, is consistent with the results of the ligation data, and suggests that the large observed extensibility in fibrin fibers is mediated by the natively unfolded regions of the molecule. Although some models attribute fibrin's force-versus-extension behavior to unfolding of structured regions within the monomer, our analysis argues that these models are inconsistent with the measured extensibility and elastic modulus.     

Contrasting dynamics of water and mineral nutrients in stems shown by stable isotope tracers and cryo‐SIMS

Lateral exchange of water and nutrients between xylem and surrounding tissues helps to de‐couple uptake from utilization in all parts of a plant. We studied the dynamics of these exchanges, using stable isotope tracers for water (H₂¹⁸O), magnesium (²⁶Mg), potassium (⁴¹K) and calcium (⁴⁴Ca) delivered via a cut stem for various periods to the transpiration stream of bean shoots (Phaseolus vulgaris cv. Fardenlosa Shiny). Tracers were subsequently mapped in stem cross‐sections with cryo‐secondary ion mass spectrometry. The water tracer equilibrated within minutes across the entire cross‐section. In contrast, the nutrient tracers showed a very heterogeneous exchange between xylem vessels and the different stem tissues, even after 4 h. Dynamics of nutrients in the tissues revealed a fast and extensive exchange of nutrients in the xylem parenchyma, with, for example, calcium being completely replaced by tracer in less than 5 min. Dilution of potassium tracer during its 30 s transit in xylem sap through the stem showed that potassium concentration was up‐regulated over many hours, to the extent that some of it was probably supplied by phloem recirculation from the shoot.     

Effects of lipid phase transition of the freeze-cleaved envelope of Escherichia coli.

We studied the fine structure of the envelope of Escherichia coli auxotroph K1060 after the cells were grown in the presence of one of the following fatty acids; oleic, palmitelaidic, or elidic acid. The cells were freeze-fractured after exposure to temperatures above and below the lipid phase transition range. As judged by freeze-etching methods, we observed that below the transition range the fracture plane of the inner membrane showed the typical aggregation of intramembranous particles (IMP) and concomitant development of areas devoid of IMP. In these areas we found a regular arrangement of equally spaced ridges, often intersected at 90 degrees by arrays of similar ridges. The ridges were composed of spherical particles measuring 4 to 5 nm in diameter. Formation and melting of these arrays took place within 15 to 30s after temperature shift-down or shift-up, respectively. Fixation in glutaraldehyde prevented these changes. The outer-membrane fracture plane revealed ordered areas to a lesser degree; these were discernible only by the regular arrangement of the IMP of the concave fracture plane. We interpret the data by suggesting that the pattern of ridges in E. coli K1060 is analogous to the band patterns described for artificial liposomes, and that the particles, possibly proteins, are lined up or extruded along the ridges during membrane lipid crystallization.     

A review of the Pterogeniidae (Goleoptera)

The Pterogeniidae, a family of beetles from Indoaustralia, are revised. They comprise five genera and 24 species. Three genera and 17 species are described as new and one species is synonymized. It is shown that the male and particularly the female genitalia provide useful means for species definition. The phylogenetic relationships are discussed based on a cladistic analysis of 23 morphological characters using PAUP. The analysis resulted in a single cladogram with following grouping: ( Kryptogenius + ( Tychogenius + ( Katagenius + ( Plerogenins + Histanocerus )))). For rooting the cladogram and polarizing the characters, Sivacrypticus indicus (Archeocrypticidae) was used as an outgroup. The majority of the species is restricted to insular tropical Asia and Oceania but four of them extend their range onto the Malayan Peninsula. Another four species are known only from continental Asia, i.e. two species from South India and one each from Malayan Peninsula and Vietnam respectively. Species of Kryptogenius, Pterogenius, Katagenius and Tychogenius are highly endemic and could therefore potentially be useful for analysing areas of endemism. For this, however, the cladistic relationships should be resolved at species level. Species of Histanocerus are more widely distributed but none is found on both sides of Wallace's line.     

Preserved contractile function despite atrophic remodeling in unloaded rat hearts

The present study was designed to determine whether myocardial atrophy is necessarily associated with changes in cardiac contractility. Myocardial unloading of normal hearts was produced via heterotopic transplantation in rats. Contractions of isolated myocytes (1.2 mM Ca2+; 37 degrees C) were assessed during field stimulation (0.5, 1.0, and 2.0 Hz), and papillary muscle contractions were assessed during direct stimulation (2.0 mM Ca2+; 37 degrees C; 0.5 Hz). Hemodynamic unloading was associated with a 41% decrease in median myocyte volume and proportional decreases in myocyte length and width. Nevertheless, atrophic myocytes had normal fractional shortening, time to peak contraction, and relaxation times. Despite decreases in absolute maximal force generation (F(max)), there were no differences in F(max)/ area in papillary muscles isolated from unloaded transplanted hearts. Therefore, atrophic remodeling after unloading is associated with intact contractile function in isolated myocytes and papillary muscles when contractile indexes are normalized to account for reductions in cell length and cross-sectional area, respectively. Nevertheless, in the absence of compensatory increases in contractile function, reductions in myocardial mass will lead to impaired overall work capacity.     

An innovative approach for locating and evaluating subsurface pathways for nitrogen loss

Fundamental watershed-scale processes governing chemical flux to neighboring ecosystems are so poorly understood that effective strategies for mitigating chemical contamination cannot be formulated. Characterization of evapotranspiration, surface runoff, plant uptake, subsurface preferential flow, behavior of the chemicals in neighboring ecosystems, and an understanding of how crop management practices influence these processes are needed. Adequate characterization of subsurface flow has been especially difficult because conventional sampling methods are ineffective for measuring preferential flow of water and solutes. A sampling strategy based on ground-penetrating radar (GPR) mapping of subsurface structures coupled with near real-time soil moisture data, surface topography, remotely sensed imagery, and a geographic information system (GIS) appears to offer a means of accurately identifying subsurface preferential flow pathways. Four small adjacent watersheds draining into a riparian wetland and first-order stream at the USDA-ARS Beltsville Agricultural Research Center, Beltsville, MD are being studied with this protocol. The spatial location of some preferential flow pathways for chemicals exiting these agricultural watersheds to the neighboring ecosystems have been identified. Confirmation of the pathways is via examination of patterns in yield monitor data and remote sensing imagery.     

Behaviorally measured tactile sensitivity in the common bottlenose dolphin,Tursiops truncatus

Little research has been conducted on the somatosensory system of toothed whales and it remains uncertain how tactile sensitivity varies about their bodies. In this study, tactile sensitivity to high-frequency (250-Hz) displacement of the skin was quantified in three trained adult common bottlenose dolphins (Tursiops truncatus) using a vibratory device (tactor). The magnitude of skin displacement was controlled by varying the voltage to the tactor held against the skin surface with a constant force. Tactile thresholds were determined using an adaptive method of limits in which dolphins reported perception of the tactile stimulus by producing a whistle. Displacement thresholds ranged from 2.4 to 40 μm, with the greatest sensitivity found along the rostrum, melon, and blowhole. Sensitivity decreased caudally along the body, with the dorsal fin and tip of the fluke being the least sensitive locations tested. The results support hypotheses that the follicles on the dolphin rostrum are particularly important for perception. The reduction in tactile sensitivity at the appendages is consistent with their primary role in stabilization and locomotion compared to exploration or environmental sensing.     

Impact of Prior Seasonal H3N2 Influenza Vaccination or Infection on Protection and Transmission of Emerging Variants of Influenza A(H3N2)v Virus in Ferrets

Influenza H3N2 A viruses continue to circulate in swine and occasionally infect humans, resulting in outbreaks of variant influenza H3N2 [A(H3N2)v] virus. It has been previously demonstrated in ferrets that A(H3N2)v viruses transmit as efficiently as seasonal influenza viruses, raising concern over the pandemic potential of these viruses. However, A(H3N2)v viruses have not acquired the ability to transmit efficiently among humans, which may be due in part to existing cross-reactive immunity to A(H3N2)v viruses. Although current seasonal H3N2 and A(H3N2)v viruses are antigenically distinct from one another, historical H3N2 viruses have some antigenic similarity to A(H3N2)v viruses and previous exposure to these viruses may provide a measure of immune protection sufficient to dampen A(H3N2)v virus transmission. Here, we evaluated whether prior seasonal H3N2 influenza virus vaccination or infection affects virus replication and transmission of A(H3N2)v virus in the ferret animal model. We found that the seasonal trivalent inactivated influenza virus vaccine (TIV) or a monovalent vaccine prepared from an antigenically related 1992 seasonal influenza H3N2 (A/Beijing/32/1992) virus failed to substantially reduce A(H3N2)v (A/Indiana/08/2011) virus shedding and subsequent transmission to naive hosts. Conversely, ferrets primed by seasonal H3N2 virus infection displayed reduced A(H3N2)v virus shedding following challenge, which blunted transmission to naive ferrets. A higher level of specific IgG and IgA antibody titers detected among infected versus vaccinated ferrets was associated with the degree of protection offered by seasonal H3N2 virus infection. The data demonstrate in ferrets that the efficiency of A(H3N2)v transmission is disrupted by preexisting immunity induced by seasonal H3N2 virus infection.     

Luteinising hormone,follicle stimulating hormone and gonadotropin releasing hormone immunoreactivity in two insects: Locusta migratoria migratoroides R&F and Sarcophaga bullata (Parker)

Summary

Materials immunologically related to luteinising hormone (LH), follicle stimulating hormone (FSH) and the gonadotropin releasing hormone (GnRH) were localised in cerebral tissue of Locusta migratoria and Sarcophaga bullata by means of the peroxidase-antiperoxidase method. Several polyclonal and a monoclonal antisera were used. From the third larval instar a positive reaction was observed in cells located in several parts of the brain. Each antiserum reacted with a constant number of well defined cells and nerve fibers. No differences between sexes were observed.