Glycoprotein Ib cross-linking/ligation on echicetin-coated surfaces or echicetin-IgMkappa in stirred suspension activates platelets by cytoskeleton modulated calcium release

Cross-linking platelet GPIb with the snake C-type lectin echicetin provides a specific technique for activation via this receptor. This allows GPIb-dependent mechanisms to be studied without the necessity for shear stress-induced binding of von Willebrand factor or primary alpha(IIb)beta(3) involvement. We already showed that platelets are activated, including tyrosine phosphorylation, by echicetin-IgMkappa-induced GPIb cross-linking. We now investigate the mechanism further and demonstrate that platelets, without modulator reagents, spread directly on an echicetin-coated surface, by a GPIb-specific mechanism, causing exocytosis of alpha-granule markers (P-selectin) and activation of alpha(IIb)beta(3). This spreading requires actin polymerization and release of internal calcium stores but is not dependent on external calcium nor on src family tyrosine kinases. Cross-linking of GPIb complex molecules on platelets, either in suspension or via specific surface attachment, is sufficient to induce platelet activation.

Linking physiology with behaviour: Functional specialisation of the visual field is reflected in gaze patterns during visual search

Based on neurophysiological findings and a grid to score binocular visual field function, two hypotheses concerning the spatial distribution of fixations during visual search were tested and confirmed in healthy participants and patients with homonymous visual field defects. Both groups showed significant biases of fixations and viewing time towards the centre of the screen and the upper screen half. Patients displayed a third bias towards the side of their field defect, which represents oculomotor compensation. Moreover, significant correlations between the extent of these three biases and search performance were found. Our findings suggest a new, more dynamic view of how functional specialisation of the visual field influences behaviour.

Structural model of the CopA copper ATPase of Enterococcus hirae based on chemical cross-linking

The CopA copper ATPase of Enterococcus hirae belongs to the family of heavy metal pumping CPx-type ATPases and shares 43% sequence similarity with the human Menkes and Wilson copper ATPases. Due to a lack of suitable protein crystals, only partial three-dimensional structures have so far been obtained for this family of ion pumps. We present a structural model of CopA derived by combining topological information obtained by intramolecular cross-linking with molecular modeling. Purified CopA was cross-linked with different bivalent reagents, followed by tryptic digestion and identification of cross-linked peptides by mass spectrometry. The structural proximity of tryptic fragments provided information about the structural arrangement of the hydrophilic protein domains, which was integrated into a three-dimensional model of CopA. Comparative modeling of CopA was guided by the sequence similarity to the calcium ATPase of the sarcoplasmic reticulum, Serca1, for which detailed structures are available. In addition, known partial structures of CPx-ATPase homologous to CopA were used as modeling templates. A docking approach was used to predict the orientation of the heavy metal binding domain of CopA relative to the core structure, which was verified by distance constraints derived from cross-links. The overall structural model of CopA resembles the Serca1 structure, but reveals distinctive features of CPx-type ATPases. A prominent feature is the positioning of the heavy metal binding domain. It features an orientation of the Cu binding ligands which is appropriate for the interaction with Cu-loaded metallochaperones in solution. Moreover, a novel model of the architecture of the intramembranous Cu binding sites could be derived.

Zebrafish (Danio rerio) neuromast: promising biological endpoint linking developmental and toxicological studies

Aquatic toxicology is facing the challenge to assess the impact of complex mixtures of compounds on diverse biological endpoints. So far, ecotoxicology focuses mainly on apical endpoints such as growth, lethality and reproduction, but does not consider sublethal toxic effects that may indirectly cause ecological effects. One such sublethal effect is toxicant-induced impairment of neurosensory functions which will affect important behavioural traits of exposed organisms. Here, we critically review the mechanosensory lateral line (LL) system of zebrafish as a model to screen for chemical effects on neurosensory function of fish in particular and vertebrates in general. The LL system consists of so-called neuromasts, composed of centrally located sensory hair cells, and surrounding supporting cells. The function of neuromasts is the detection of water movements that is essential for the fish's ability to detect prey, to escape predator, to socially interact or to show rheotactic behaviour. Recent advances in the study of these organs provided researchers with a broad area of molecular tools for easy and rapid detection of neuromasts dysfunction and/or disturbed development. Further, genes involved in neuromasts differentiation have been identified using auditory/mechanosensory mutants and morphants. A number of environmental toxicants including metals and pharmaceuticals have been shown to affect neuromasts development and/or function. The use of the LL organ for toxicological studies offers the advantage to integrate the available profound knowledge on developmental biology of the neuromasts with the study of chemical toxicity. This combination may provide a powerful tool in environmental risk assessment.

Linking brain connectivity across different time scales with electroencephalogram, functional magnetic resonance imaging, and diffusion tensor imaging

Structural and functional connectivity are intrinsic properties of the human brain and represent the amount of cognitive capacities of individual subjects. These connections are modulated due to development, learning, and disease. Momentary adaptations in functional connectivity alter the structural connections, which in turn affect the functional connectivity. Thus, structural and functional connectivity interact on a broad timescale. In this study, we aimed to explore distinct measures of connectivity assessed by functional magnetic resonance imaging and diffusion tensor imaging and their association to the dominant electroencephalogram oscillatory property at rest: the individual alpha frequency (IAF). We found that in 21 healthy young subjects, small intraindividual temporal IAF fluctuations were correlated to increased blood oxygenation level-dependent signal in brain areas associated to working memory functions and to the modulation of attention. These areas colocalized with functionally connected networks supporting the respective functions. Furthermore, subjects with higher IAF show increased fractional anisotropy values in fascicles connecting the above-mentioned areas and networks. Hence, due to a multimodal approach a consistent functionally and structurally connected network related to IAF was observed.

Addressing micropollution by linking problem characteristics to policy instruments

What characterizes micropollution as a policy problem and which policy instruments are adequate to regulate micropollution, given the specific problem features? In this article, problem characteristics of micropollution are systematically analyzed and linked to potential policy solutions.

Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)

The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia, where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra and on accurately dated European stalagmites, the Toba event is known to occur between the onsets of Greenland interstadials (GI) 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 ka BP) before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM-19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. The bipolar linking gives no support for a long-term global cooling caused by the Toba eruption as Antarctica experiences a major warming shortly after the event. Furthermore, our bipolar match provides a way to place palaeo-environmental records other than ice cores into a precise climatic context.

Linking local knowledge, conservation practices and ecosystem diversity: comparing two communities in the Tunari National Park (Bolivia)

Combined approaches to conserve both biological and cultural diversity are seen as an alternative to classical nature conservation instruments. The objective of this study was to examine the influence of urbanization coupled with exclusive conservation measures, on land use, local knowledge and biodiversity in two Quechua speaking communities of Bolivia located within the Tunari National Park. We assessed and compared the links between land use, its transformation through conservation practices, local institutions and the worldviews of both communities and the implications they have for biodiversity at the level of ecosystems. Our results show that in both communities, people’s worldviews and environmental knowledge are linked with an integral and diversified use of their territory. However, the community most affected by urbanization and protected area regulations has intensified agriculture in a small area and has abandoned the use of large areas. This was accompanied by a loss of local environmental knowledge and a decrease in the diversity of ecosystems. The second community, where the park was not enforced, continues to manage their territory as a material expression of local environmental knowledge, while adopting community-based conservation measures with external support. Our findings highlight a case in which urbanization coupled with exclusive conservation approaches affects the components of both cultural and biological diversity. Actions that aim to enhance biocultural diversity in this context should therefore address the impact of factors identified as responsible for change in integrated social-ecological systems.

Protein cross-linking mediated by tissue transglutaminase correlates with the maturation of extracellular matrices during lung development

At birth, the mammalian lung is still immature. The alveoli are not yet formed and the interairspace walls contain two capillary layers which are separated by an interstitial core. After alveolarization (first 2 postnatal weeks in rats) the alveolar septa mature: their capillary layers merge, the amount of connective tissue decreases, and the mature lung parenchyma is formed (second and third week). During the first 3 wk of life the role of tissue transglutaminase (tTG) was studied in rat lung by immunostaining of cryostat and paraffin sections, by Northern and Western blotting, and by a quantitative determination of gamma-glutamyl-epsilon-lysine. While enzyme activity and intracellular tTG were already present before term, the enzyme product (gamma-glutamyl-epsilon-lysine-crosslink) and extracellular tTG appeared between postnatal days 10 and 19 in the lung parenchyma. In large blood vessels and large airways, which mature earlier than the parenchyma, both the enzyme product and extracellular tTG had already appeared at the end of the first postnatal week. We conclude that tTG is expressed and externalized into the extracellular matrix of lung shortly before maturation of an organ area. Because tTG covalently and irreversibly crosslinks extracellular matrix proteins, we hypothesize that it may prevent or delay further remodeling of basement membranes and may stabilize other extracellular components, such as microfibrils.