Anthracen-derivate in kalluskulturen aus Cassia angustifolia

Callus cultures from cotyledons of Cassia angustifolia were shown to contain dianthrones. Proof of their structures was obtained by co-chromatography (TLC), oxidative cleavage and UV analysis. The basic components chrysophanol, physcion, rheum emodin, aloe emodin and rhein have been isolated and identified by UV and IR analysis.     

One-step refolding and purification of disulfide-containing proteins with a C-terminal MESNA thioester

Background  

Expression systems based on self-cleavable intein domains allow the generation of recombinant proteins with a C-terminal thioester. This uniquely reactive C-terminus can be used in native chemical ligation reactions to introduce synthetic groups or to immobilize proteins on surfaces and nanoparticles. Unfortunately, common refolding procedures for recombinant proteins that contain disulfide bonds do not preserve the thioester functionality and therefore novel refolding procedures need to be developed.     

Changes in gape frequency, siphon activity and thermal response in the freshwater bivalves Anodonta cygnea and Margaritifera falcata

Physiologically-driven rhythms in bivalve molluscs are predictedto vary as a function of metabolic rate and temperature, incontrast to genetically predisposed biological clocks. Theserhythms can be evaluated using long-term video monitoring techniquesunder controlled conditions in laboratory aquaria. The bivalvesAnodonta cygnea and Margaritifera falcata were used to evaluatethe effect of temperature on rhythms in gape and the formationof siphons at the mantle edge. Frequency and duration of shellclosure vary with temperature in both species, but with differentresponses. Mean duration of intervals of valve closure decreasesas temperature rises in both species, and is consistent withphysiological limitation by increased biological oxygen demand.For A. cygnea, cumulative gape duration peaks at 25°C, withless time spent closed than at any other temperature, but increasingtemperatures correspond to an increase in gape frequency witha strong increase observed at 31°C. In contrast, frequencyof adduction and valve closure peak at 25°C in M. falcata,and continuous gaping is observed above 29.5°C. This physiologicalstress is consistent with evidence from sclerochronologically-calibratedstable isotope studies of shells, where growth breaks in manymarine taxa coincide with maximum temperatures above 31°Cas derived for ¹⁸O_carbonate. The results of this study suggestthat these growth breaks may be due to physiological limitationsin oxygen uptake and metabolic activity, rather than being adirect consequence of elevated temperature alone. (Received 17 March 2008; accepted 3 October 2008)     

Integrating gene expression and GO classification for PCA by preclustering

Background  

Gene expression data can be analyzed by summarizing groups of individual gene expression profiles based on GO annotation information. The mean expression profile per group can then be used to identify interesting GO categories in relation to the experimental settings. However, the expression profiles present in GO classes are often heterogeneous, i.e., there are several different expression profiles within one class. As a result, important experimental findings can be obscured because the summarizing profile does not seem to be of interest. We propose to tackle this problem by finding homogeneous subclasses within GO categories: preclustering.     

Molecular and Cellular Mechanisms of Lamina-specific Axon Targeting

The specificity of synaptic connections is directly related to the functional integrity of neural circuits. Long-range axon guidance and topographic mapping mechanisms bring axons into spatial proximity of target cells and thus limit the number of potential synaptic partners. Synaptic specificity is then achieved by extracellular short-range guidance cues and cell-surface recognition cues. Neural activity may enhance the precision and strength of specific circuit connections. Here, we focus on one of the final steps of synaptic matchmaking: the targeting of synaptic layers and the mutual recognition of axons and dendrites within these layers.Perception and behavior are critically dependent on synaptic communication between specific neurons. Understanding how neurons achieve such “synaptic specificity” is therefore one of the most fundamental issues in developmental neuroscience. Langley’s notion of “chemical relations” between synaptically connected neurons (Langley 1892) and Sperry’s “chemoaffinity” hypothesis (Sperry 1963) provided a conceptual framework for the development of precise synaptic connections in the central nervous system. Sperry postulated that molecular interactions between neurons and their extracellular environment (including between and amongst axons and dendrites) ensure that connections form only between “appropriate” synaptic partners (Sperry 1963). This hypothesis has been confirmed by experimental work over the last four decades, most importantly by the identification of molecular cues that provide synaptic specificity (see Sanes and Yamagata 2009 for a recent comprehensive review). However, within this broad framework, a number of alternate mechanisms have been shown or proposed to play roles in specific aspects of such targeting processes. Here, we focus on mechanisms that underlie the formation of synaptic layers, a prominent anatomical feature of the visual system as well as many other areas of the CNS.As reviewed previously (O''Leary 2010), the chemoaffinity principle underlies the developmental process of topographic mapping. Indeed, the precision with which neurons preserve the spatial relationships between the visual world and its representation in the brain is remarkable: Across animals ranging from flies to vertebrates, axons that bear signals from adjacent points in visual space invariably choose adjacent targets in the brain (Braitenberg 1967; Lemke and Reber 2005; Sperry 1963). Thus, position-dependent guidance of axons ensures that a visuotopic map develops. However, position in space is just one attribute of a visual stimulus; others include color, brightness, edge detection, and movement. If position in visual space is encoded by localized activation within a two-dimensional field of neurons, then these other features are encoded by local circuits that act both in series and in parallel and are reiterated many times across the field (Fig. 1). These local circuit modules are often envisioned as “columns” that lie orthogonal to the topographic map, with each column corresponding to a pixel in visual space and each level of the column representing a different, specific visual feature within that pixel, such as brightness, color, etc. (Fig. 1). How these columns acquire their laminated structure represents a developmental challenge of extraordinary scale. Although long-range axon guidance and topographic mapping no doubt contribute to restricting the astronomical number of potential synaptic partners, these mechanisms are clearly not sufficient; additional mechanisms must (and do) exist that act on a local scale to provide an additional level of positional information and cell-type-specific “chemoaffinity.”Open in a separate windowFigure 1.Laminae are a fundamental organizing unit of neural circuits. Each column corresponds to a single topographic position (e.g., location on the retina). Within each column, different cell types (shown type A: blue, and type B: red) respond to different features in the visual world, such as motion or luminance. These pixels are repeated many times over and thus cover all of visual space. A simple rule of “Cell type A connects to Layer A, etc.” ensures that functional segregation is maintained in the connections from the retina to the target (parallel processing). Each pixel P1, P2, and P3 connects to a single column (C1, C2, and C3), establishing serial processing. Within each column, there are local circuits that, too, are layer-specific. Thus, laminae ensure functional specificity of both afferent-target connections and local circuit connections.A prominent principle, which guides the formation of connections between specific cell types and is a characteristic feature of CNS architecture, is the concentration of synapses in small areas. These synapse clusters can take the form of planar layers or spherical glomeruli. Although glomeruli are a specialization that appears most prominent in the olfactory system, layers, or laminae, are an almost ubiquitous feature of central nervous system architecture. Indeed, even crude histological stains reveal that axons and dendrites often accumulate in neuropil (cell-body-free areas). Cell-type-specific or single-cell labeling has shown that, within individual neuropil layers, neurites and synapses are not distributed randomly. Rather, synaptic connections arising between neurons with the same or similar functional properties are localized to particular sublaminae that distinguish synapses with different properties (Fig. 1). The structural underpinnings of this functional principle are provided by mechanisms that ensure the lamina-specific branching of the corresponding neurites. How this enormous precision is achieved is the subject of intense investigations in the Drosophila, zebrafish, chick, and mouse visual systems. We will begin by describing three anatomical regions in these model organisms. Then, we will discuss three broad principles of layer-specific targeting in the visual system, namely cell–cell recognition, guidance by matrix cues, and activity-dependent sorting of axon terminals.     

Essential role of E3 ubiquitin ligase activity in Cbl-b-regulated T cell functions

E3 ubiquitin ligases have been placed among the essential molecules involved in the regulation of T cell functions and T cell tolerance. However, it has never been experimentally proven in vivo whether these functions indeed depend on the catalytic E3 ligase activity. The Casitas B-cell lymphoma (Cbl) family protein Cbl-b was the first E3 ubiquitin ligase directly implicated in the activation and tolerance of the peripheral T cell. In this study, we report that selective genetic inactivation of Cbl-b E3 ligase activity phenocopies the T cell responses observed when total Cbl-b is ablated, resulting in T cell hyperactivation, spontaneous autoimmunity, and impaired induction of T cell anergy in vivo. Moreover, mice carrying a Cbl-b E3 ligase-defective mutation spontaneously reject tumor cells that express human papilloma virus Ags. These data demonstrate for the first time, to our knowledge, that the catalytic function of an E3 ligase, Cbl-b, is essential for negative regulation of T cells in vivo. Thus, modulation of the E3 ligase activity of Cbl-b might be a novel modality to control T cell immunity in vaccination, cancer biology, or autoimmunity.