Stopping vs. staging: the difference between a hop and a jump

Places where migrant birds stop to rest, drink, and eat at are often described as either stopover or staging sites. Attempts have been made to differentiate between these two terms but they are frequently used interchangeably. Some authors have equated staging sites with sites that attract large concentrations (many thousands) of birds, a definition that others have expanded to include long stopover durations and significant rates of refueling on predictable, abundant prey. It has also been suggested that birds using staging sites are those that employ a jumping strategy during migration. I argue that while all sites where birds rest and feed during migration are stopover sites, further classification of stopover sites is of ecological and conservation value. I propose that sites with abundant, predictable food resources where birds prepare for an energetic challenge (usually a long flight over a barrier such as an ocean or a desert) requiring substantial fuel stores and physiological changes without which significant fitness costs are incurred are most appropriately described as staging sites.     

Genetic biodiversity in the Baltic Sea: species-specific patterns challenge management

Information on spatial and temporal patterns of genetic diversity is a prerequisite to understanding the demography of populations, and is fundamental to successful management and conservation of species. In the sea, it has been observed that oceanographic and other physical forces can constitute barriers to gene flow that may result in similar population genetic structures in different species. Such similarities among species would greatly simplify management of genetic biodiversity. Here, we tested for shared genetic patterns in a complex marine area, the Baltic Sea. We assessed spatial patterns of intraspecific genetic diversity and differentiation in seven ecologically important species of the Baltic ecosystem—Atlantic herring (Clupea harengus), northern pike (Esox lucius), European whitefish (Coregonus lavaretus), three-spined stickleback (Gasterosteus aculeatus), nine-spined stickleback (Pungitius pungitius), blue mussel (Mytilus spp.), and bladderwrack (Fucus vesiculosus). We used nuclear genetic data of putatively neutral microsatellite and SNP loci from samples collected from seven regions throughout the Baltic Sea, and reference samples from North Atlantic areas. Overall, patterns of genetic diversity and differentiation among sampling regions were unique for each species, although all six species with Atlantic samples indicated strong resistence to Atlantic-Baltic gene-flow. Major genetic barriers were not shared among species within the Baltic Sea; most species show genetic heterogeneity, but significant isolation by distance was only detected in pike and whitefish. These species-specific patterns of genetic structure preclude generalizations and emphasize the need to undertake genetic surveys for species separately, and to design management plans taking into consideration the specific structures of each species.     

Load-shift--numerical evaluation of a new design philosophy for uncemented hip prostheses

All hip replacement prostheses alter the load transfer from the hip joint into the femur by changing the mechanical loading of the proximal femur from an externally to an internally loaded system. This alteration of the load transfer causes stress shielding and might lead to severe bone loss, especially with uncemented prostheses. To minimize these effects, load transfer to the femur should occur as proximal as possible. In order to support sufficient primary stability, however, directly post operative (PO) distal stabilization is reasonable. Consequently, the prostheses have to alter its mechanical characteristics after implantation. This concept is referred to as load-shift concept. Primary stability during the early PO state is provided by a prosthesis shaft, which is widened at the tip by a biodegradable pin. After resorption of the pin load transfer occurs no longer distally. The objective of this study was the numerical evaluation of the load-shift concept. The analysis was performed with a finite element model. Three-dimensional non-linear dynamic gait analyses data were used to evaluate whether the load transfer during walking can be altered effectively by insertion and resorption of a distal pin. Directly PO 38% of the transverse load is transferred through the prosthesis shaft and micromotion of the proximal prostheses tip is below 55 microm. After resorption of the pin, no transverse loads are transferred through the prosthesis shaft. Therefore, the loading of the proximal bone tissue is far more pronounced than in the case of a standard prosthesis, demonstrating the feasibility of the load-shift concept. A balanced degradation of the pin simultaneously with the ingrowth of the prosthesis is expected to reduce hip replacement complications.     

Process monitoring of virus-like particle reassembly by diafiltration with UV/Vis spectroscopy and light scattering

Virus-like particles (VLPs) have shown great potential as biopharmaceuticals in the market and in clinics. Nonenveloped, in vivo assembled VLPs are typically disassembled and reassembled in vitro to improve particle stability, homogeneity, and immunogenicity. At the industrial scale, cross-flow filtration (CFF) is the method of choice for performing reassembly by diafiltration. Here, we developed an experimental CFF setup with an on-line measurement loop for the implementation of process analytical technology (PAT). The measurement loop included an ultraviolet and visible (UV/Vis) spectrometer as well as a light scattering photometer. These sensors allowed for monitoring protein concentration, protein tertiary structure, and protein quaternary structure. The experimental setup was tested with three Hepatitis B core Antigen (HBcAg) variants. With each variant, three reassembly processes were performed at different transmembrane pressures (TMPs). While light scattering provided information on the assembly progress, UV/Vis allowed for monitoring the protein concentration and the rate of VLP assembly based on the microenvironment of Tyrosine-132. VLP formation was verified by off-line dynamic light scattering (DLS) and transmission electron microscopy (TEM). Furthermore, the experimental results provided evidence of aggregate-related assembly inhibition and showed that off-line size-exclusion chromatography does not provide a complete picture of the particle content. Finally, a Partial-Least Squares (PLS) model was calibrated to predict VLP concentrations in the process solution. values of 0.947–0.984 were reached for the three HBcAg variants. In summary, the proposed experimental setup provides a powerful platform for developing and monitoring VLP reassembly steps by CFF.     

Prescribing diatom morphology: toward genetic engineering of biological nanomaterials

The formation of inorganic materials with complex form is a widespread biological phenomenon (biomineralization). Among the most spectacular examples of biomineralization is the production by diatoms (a group of eukaryotic microalgae) of intricately nanopatterned to micropatterned cell walls made of silica (SiO2). Understanding the molecular mechanisms of diatom silica biomineralization is not only a fundamental biological problem, but also of great interest in materials engineering, as the biological self-assembly of three-dimensional (3D) inorganic nanomaterials has no man-made analog. Recently, insight into the molecular mechanism of diatom silica formation has been obtained by structural and functional analysis of biomolecules that are involved in this process. Furthermore, the rapid development of diatom molecular genetics has provided new tools for investigating the silica forming machinery of diatoms and for manipulating silica biogenesis. This has opened the door for the production, through genetic engineering, of unique 3D nanomaterials with designed structures and functionalities.     

Extracellular proteolytic cleavage by urokinase is required for activation of hepatocyte growth factor/scatter factor.

The extracellular protease urokinase is known to be crucially involved in morphogenesis, tissue repair and tumor invasion by mediating matrix degradation and cell migration. Hepatocyte growth factor/scatter factor (HGF/SF) is a secretory product of stromal fibroblasts, sharing structural motifs with enzymes of the blood clotting cascade, including a zymogen cleavage site. HGF/SF promotes motility, invasion and growth of epithelial and endothelial cells. Here we show that HGF/SF is secreted as a single-chain biologically inactive precursor (pro-HGF/SF), mostly found in a matrix-associated form. Maturation of the precursor into the active alpha beta heterodimer takes place in the extracellular environment and results from a serum-dependent proteolytic cleavage. In vitro, pro-HGF/SF was cleaved at a single site by nanomolar concentrations of pure urokinase, generating the active mature HGF/SF heterodimer. This cleavage was prevented by specific urokinase inhibitors, such as plasminogen activator inhibitor type-1 and protease nexin-1, and by antibodies directed against the urokinase catalytic domain. Addition of these inhibitors to HGF/SF responsive cells prevented activation of the HGF/SF precursor. These data show that urokinase acts as a pro-HGF/SF convertase, and suggest that some of the growth and invasive cellular responses mediated by this enzyme may involve activation of HGF/SF.     

Über ependymale Gliazellen in der Commissura caudalis und habenularis der Katze

Zusammenfassung An 5–8 Tage alten Katzen wurden im Ependym der Commissura caudalis sog. ependymale Gliazellen beobachtet, die wahrscheinlich embryonaler Natur sind. Bei älteren Katzen sind diese Zellen nicht nachweisbar; sie scheinen durch Astrocyten ersetzt zu werden.Die Commissura habenularis der 3 Monate alten Katze enthält dort, wo sie der Epiphyse unmittelbar aufliegt, wenige Astrocyten, deren Fortsätze fast bis zur Zirbelspitze ausstrahlen.