Making water flow: a comparison of the hydrodynamic characteristics of 12 different benthic biological flumes

Flume tanks are becoming increasingly important research tools in aquatic ecology, to link biological to hydrodynamical processes. There is no such thing as a “standard flume tank”, and no flume tank is suitable for every type of research question. A series of experiments has been carried out to characterise and compare the hydrodynamic characteristics of 12 different flume tanks that are designed specifically for biological research. These facilities are part of the EU network BioFlow. The flumes could be divided into four basic design types: straight, racetrack, annular and field flumes. In each facility, two vertical velocity profiles were measured: one at 0.05 m s⁻¹ and one at 0.25 m s⁻¹. In those flumes equipped with Acoustic Doppler Velocimeters (ADV), time series were also recorded for each velocity at two heights above the bottom: 0.05 m and 20% of the water depth. From these measurements turbulence characteristics, such as TKE and Reynolds stress, were derived, and autocorrelation spectra of the horizontal along-stream velocity component were plotted. The flume measurements were compared to two sets of velocity profiles measured in the field.Despite the fact that some flumes were relatively small, turbulence was fully developed in all channels. Straight and racetrack flumes generally produced boundary layers with a clearly definable logarithmic layer, similar to measurements in the field taken under steady flow conditions. The two annular flumes produced relatively thin boundary layers, presumably due to secondary flows developing in the curved channels. The profiles in the field flumes also differed considerably from the expected log profile. This may either have been due the construction of the flume, or due to unsteady conditions during measurement. Constraints imposed by the different flume designs on the suitability for different types of boundary layer research, as well as scaling issues are discussed.     

Phagocytosis and Respiratory Burst Activity in Lumpsucker (Cyclopterus lumpus L.) Leucocytes Analysed by Flow Cytometry

In the present study, we have isolated leucocytes from peripheral blood, head kidney and spleen from lumpsucker (Cyclopterus lumpus L.), and performed functional studies like phagocytosis and respiratory burst, as well as morphological and cytochemical analyses. Different leucocytes were identified, such as lymphocytes, monocytes/macrophages and polymorphonuclear cells with bean shaped or bilobed nuclei. In addition, cells with similar morphology as described for dendritic cells in trout were abundant among the isolated leucocytes. Flow cytometry was successfully used for measuring phagocytosis and respiratory burst activity. The phagocytic capacity and ability were very high, and cells with different morphology in all three leucocyte preparations phagocytised beads rapidly. Due to lack of available cell markers, the identity of the phagocytic cells could not be determined. The potent non-specific phagocytosis was in accordance with a high number of cells positive for myeloperoxidase, an enzyme involved in oxygen-dependent killing mechanism present in phagocytic cells. Further, high respiratory burst activity was present in the leucocytes samples, verifying a potent oxygen- dependent degradation. At present, the specific antibody immune response could not be measured, as immunoglobulin or B-cells have not yet been isolated. Therefore, analyses of the specific immune response in this fish species await further clarification. The present study presents the first analyses of lumpsucker immunity and also the first within the order Scopaeniformes.     

Age class,density and temporal effects on diet composition of sheep in an alpine ecosystem

Understanding diet selection is important since diet determines energy intake and therefore growth of ungulate populations. Yet very few studies have reported annual variation in diet. Density-dependent diet choice by large herbivores has been reported several times, but these studies are typically either short-term or they lack replication of the density treatment. In a landscape-scale experiment with 3 replicates of two densities (25 and 80 individuals/km²) of domestic sheep, we determined diet composition using microhistological analysis during 6 summer grazing seasons (2002–2007) in alpine habitats. We tested how age class, density and temporal variation (within season, annually, and over years) affected summer diet. There was marked evidence of additive effects of these factors on overall diet composition, but interactions were few. The interaction between density and annual variation was an important determinant of the proportion of the main forage component (Avenella flexuosa), but not of the proportions of herbs, Salix spp. and for “other” forage plants. Surprisingly, the density effect on this intermediate quality forage (A. flexuosa) was not consistent among years (both positive, negative and no effects), likely arising due to large variation in the proportion of the other forage plants. We discuss how foraging ecology can supplement the insight from life history theory in explaining variation in vital rates.     

Histone H2A Mono-Ubiquitination Is a Crucial Step to Mediate PRC1-Dependent Repression of Developmental Genes to Maintain ES Cell Identity

Two distinct Polycomb complexes, PRC1 and PRC2, collaborate to maintain epigenetic repression of key developmental loci in embryonic stem cells (ESCs). PRC1 and PRC2 have histone modifying activities, catalyzing mono-ubiquitination of histone H2A (H2AK119u1) and trimethylation of H3 lysine 27 (H3K27me3), respectively. Compared to H3K27me3, localization and the role of H2AK119u1 are not fully understood in ESCs. Here we present genome-wide H2AK119u1 maps in ESCs and identify a group of genes at which H2AK119u1 is deposited in a Ring1-dependent manner. These genes are a distinctive subset of genes with H3K27me3 enrichment and are the central targets of Polycomb silencing that are required to maintain ESC identity. We further show that the H2A ubiquitination activity of PRC1 is dispensable for its target binding and its activity to compact chromatin at Hox loci, but is indispensable for efficient repression of target genes and thereby ESC maintenance. These data demonstrate that multiple effector mechanisms including H2A ubiquitination and chromatin compaction combine to mediate PRC1-dependent repression of genes that are crucial for the maintenance of ESC identity. Utilization of these diverse effector mechanisms might provide a means to maintain a repressive state that is robust yet highly responsive to developmental cues during ES cell self-renewal and differentiation.     

Myocardial mechanical dysfunction and calcium overload following rewarming from experimental hypothermia in vivo

Rewarming patients from accidental hypothermia are regularly complicated with cardiovascular instability ranging from minor depression of cardiac output to fatal circulatory collapse also termed “rewarming shock”. Since altered Ca²⁺ handling may play a role in hypothermia-induced heart failure, we studied changes in Ca²⁺ homeostasis in in situ hearts following hypothermia and rewarming. A rat model designed for studies of the intact heart in a non-arrested state during hypothermia and rewarming was used. Rats were core cooled to 15 °C, maintained at 15 °C for 4 h and thereafter rewarmed. As time-matched controls, one group of animals was kept at 37 °C for 5 h. Total intracellular myocardial Ca²⁺ content ([Ca²⁺]_i) was measured using ⁴⁵Ca²⁺. Following rewarming we found a significant reduction of stroke volume and cardiac output compared to prehypothermic control values as well as to time-matched controls. Likewise, we found that hypothermia and rewarming resulted in a more than six-fold increase in [Ca²⁺]_i to 3.01 ± 0.43 μmol/g dry weight compared to 0.44 ± 0.05 μmol/g dry weight in normothemia control. These findings indicate that hypothermia-induced alterations in the Ca²⁺-handling result in Ca²⁺ overload during hypothermia, which may contribute to myocardial failure during and after rewarming.     

Amino sugar and amino acid constituents of the cell walls of the extremely halophilic cocci

Cell wall hydrolysates of nine strains of extremely halophilic cocci all contained glycine, glucosamine, galactosamine, and gulosaminuronic acid. Muramic acid was not present in any of the strains.     

Untersuchungen über die Maltose- und Glucosevergärung bei homozygoten Hefestämmen mit verschiedenen Genomzahlen

Ohne ZusammenfassungDissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Frein Universität Berlin 1962.     

NEIL3-Dependent Regulation of Cardiac Fibroblast Proliferation Prevents Myocardial Rupture

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