Oxysterols direct B-cell migration through EBI2

EBI2 (also called GPR183) is an orphan G-protein-coupled receptor that is highly expressed in spleen and upregulated upon Epstein-Barr-virus infection. Recent studies indicated that this receptor controls follicular B-cell migration and T-cell-dependent antibody production. Oxysterols elicit profound effects on immune and inflammatory responses as well as on cholesterol metabolism. The biological effects of oxysterols have largely been credited to the activation of nuclear hormone receptors. Here we isolate oxysterols from porcine spleen extracts and show that they are endogenous ligands for EBI2. The most potent ligand and activator is 7α,25-dihydroxycholesterol (OHC), with a dissociation constant of 450?pM for EBI2. In vitro, 7α,25-OHC stimulated the migration of EBI2-expressing mouse B and T cells with half-maximum effective concentration values around 500 pM, but had no effect on EBI2-deficient cells. In vivo, EBI2-deficient B cells or normal B cells desensitized by 7α,25-OHC pre-treatment showed reduced homing to follicular areas of the spleen. Blocking the synthesis of 7α,25-OHC in vivo with clotrimazole, a CYP7B1 inhibitor, reduced the content of 7α,25-OHC in the mouse spleen and promoted the migration of adoptively transferred pre-activated B cells to the T/B boundary (the boundary between the T-zone and B-zone in the spleen follicle), mimicking the phenotype of pre-activated B cells from EBI2-deficient mice. Our results show an unexpected causal link between EBI2, an orphan G-protein-coupled receptor controlling B-cell migration, and the known immunological effects of certain oxysterols, thus uncovering a previously unknown role for this class of molecules.     

Efficient mapping of mendelian traits in dogs through genome-wide association

With several hundred genetic diseases and an advantageous genome structure, dogs are ideal for mapping genes that cause disease. Here we report the development of a genotyping array with approximately 27,000 SNPs and show that genome-wide association mapping of mendelian traits in dog breeds can be achieved with only approximately 20 dogs. Specifically, we map two traits with mendelian inheritance: the major white spotting (S) locus and the hair ridge in Rhodesian ridgebacks. For both traits, we map the loci to discrete regions of <1 Mb. Fine-mapping of the S locus in two breeds refines the localization to a region of approximately 100 kb contained within the pigmentation-related gene MITF. Complete sequencing of the white and solid haplotypes identifies candidate regulatory mutations in the melanocyte-specific promoter of MITF. Our results show that genome-wide association mapping within dog breeds, followed by fine-mapping across multiple breeds, will be highly efficient and generally applicable to trait mapping, providing insights into canine and human health.     

Structural mechanism of plant aquaporin gating

Plants counteract fluctuations in water supply by regulating all aquaporins in the cell plasma membrane. Channel closure results either from the dephosphorylation of two conserved serine residues under conditions of drought stress, or from the protonation of a conserved histidine residue following a drop in cytoplasmic pH due to anoxia during flooding. Here we report the X-ray structure of the spinach plasma membrane aquaporin SoPIP2;1 in its closed conformation at 2.1 A resolution and in its open conformation at 3.9 A resolution, and molecular dynamics simulations of the initial events governing gating. In the closed conformation loop D caps the channel from the cytoplasm and thereby occludes the pore. In the open conformation loop D is displaced up to 16 A and this movement opens a hydrophobic gate blocking the channel entrance from the cytoplasm. These results reveal a molecular gating mechanism which appears conserved throughout all plant plasma membrane aquaporins.     

Blockade of GABAB receptors accelerates amygdala kindling development

The aim of this study was to investigate the putative role of GABA_B receptors in the development of amygdala kindling in rats. The effects of the GABA_B blocker CGP 35348 and the GABA_B agonist baclofen on the progressive development of behavioural seizure symptoms (stages 1–5 classified by Racine) and duration of afterdischarges (AD) were studied. CGP 35348 at a dose of 300 mg/kg i.p, which blocks central GABA_B receptors, moderately but consistently accelerated the development of behavioural seizure symptoms. CGP 35348 had no marked effect on the duration of ADs corresponding to the different seizure stages. L-baclofen (6 mg/kg i.p.) had a dual effect on kindling development. It retarded the development of the behavioural symptoms, but increased the duration of AD. In conclusion, the results suggest that synaptically-released GABA activated GABA_B receptors and thereby exerted a depressant effect on kindling development.     

Finding good predictors for inflation: a Bayesian model averaging approach

We consider a Bayesian model averaging approach for the purpose of forecasting Swedish consumer price index inflation using a large set of potential indicators, comprising some 80 quarterly time series covering a wide spectrum of Swedish economic activity. The paper demonstrates how to efficiently and systematically evaluate (almost) all possible models that these indicators in combination can give rise to. The results, in terms of out‐of‐sample performance, suggest that Bayesian model averaging is a useful alternative to other forecasting procedures, in particular recognizing the flexibility by which new information can be incorporated. Copyright © 2004 John Wiley & Sons, Ltd.     

Chemistry of some potent animal toxins

Conclusion I have discussed in this article only the most active toxins, with the result that many interesting substances have been omitted, e.g. the toxins from bee and wasp venoms (apamin, melittin, etc.), of many amphibians (bufotoxins, etc.), ciguatoxins, and many more. Poisons are found in every phylum except birds. Shrews exemplify venomous mammals. One gets a good illustration of the number of poisonous animals by studying the monumental and impressive work byHalstead ¹⁰⁶ which consequently excludes terrestrial animals. An interesting fact in this connection is that there are about 20,000 species of spiders, most of which are poisonous.A toxin ranking list has to be included in an article of this kind. The list is, of course, far from complete. Data on molecular weights, mouse lethal doses, etc. are lacking for many potent toxins, such as the dysentery toxin, a neurotoxin with a toxicity comparable to that of the botulinus toxins¹⁰⁷, the toxins from the jelly fishChironex fleckeri ¹⁰⁶.A comparison on molar basis gives a better notion of the toxicities. Curare has about 1/30 of the toxicity of the curarimimetic snake venom neurotoxins, clearly indicating that curare has a much lower affinity for the acetylcholine receptor.Toxic organisms have developed during millions of years more and more refined toxins, and this evolution has probably brought into existence toxins against every physiological function. Neurochemistry is to a great extent unexplored. Progress in this field will in the nearest future depend on specific toxins from various natural sources. Toxins from spiders, scorpions, snakes, frogs, and fishes are therefore not mere curiosities but valuable tools for research on the molecular mechanisms of neural function and synaptic transmission.     

Dll4 signalling through Notch1 regulates formation of tip cells during angiogenesis

In sprouting angiogenesis, specialized endothelial tip cells lead the outgrowth of blood-vessel sprouts towards gradients of vascular endothelial growth factor (VEGF)-A. VEGF-A is also essential for the induction of endothelial tip cells, but it is not known how single tip cells are selected to lead each vessel sprout, and how tip-cell numbers are determined. Here we present evidence that delta-like 4 (Dll4)-Notch1 signalling regulates the formation of appropriate numbers of tip cells to control vessel sprouting and branching in the mouse retina. We show that inhibition of Notch signalling using gamma-secretase inhibitors, genetic inactivation of one allele of the endothelial Notch ligand Dll4, or endothelial-specific genetic deletion of Notch1, all promote increased numbers of tip cells. Conversely, activation of Notch by a soluble jagged1 peptide leads to fewer tip cells and vessel branches. Dll4 and reporters of Notch signalling are distributed in a mosaic pattern among endothelial cells of actively sprouting retinal vessels. At this location, Notch1-deleted endothelial cells preferentially assume tip-cell characteristics. Together, our results suggest that Dll4-Notch1 signalling between the endothelial cells within the angiogenic sprout serves to restrict tip-cell formation in response to VEGF, thereby establishing the adequate ratio between tip and stalk cells required for correct sprouting and branching patterns. This model offers an explanation for the dose-dependency and haploinsufficiency of the Dll4 gene, and indicates that modulators of Dll4 or Notch signalling, such as gamma-secretase inhibitors developed for Alzheimer's disease, might find usage as pharmacological regulators of angiogenesis.