Nodal antagonists regulate formation of the anteroposterior axis of the mouse embryo

Patterning of the mouse embryo along the anteroposterior axis during body plan development requires migration of the distal visceral endoderm (DVE) towards the future anterior side by a mechanism that has remained unknown. Here we show that Nodal signalling and the regionalization of its antagonists are required for normal migration of the DVE. Whereas Nodal signalling provides the driving force for DVE migration by stimulating the proliferation of visceral endoderm cells, the antagonists Lefty1 and Cerl determine the direction of migration by asymmetrically inhibiting Nodal activity on the future anterior side.     

Disposable-soma senescence mediated by sexual selection in an ungulate

Senescence may result from an optimal balance between current reproductive investment and bodily repair processes required for future reproduction, a theoretical prediction difficult to prove especially in large, long-lived animals. Here we propose that teeth that have fixed dimensions early in life, but that wear during chewing, can be taken as a measure of total lifetime 'repair', and their wear rate as a measure of current expenditure in performance. Our approach also considers the sexual selection process to investigate the advance of senescence in males compared with females, when selection favouring competition over mates reduces the reproductive lifespan of males. We studied carcasses of 2,141 male and 739 female red deer (Cervus elaphus) of different ages, finding that male molariform teeth emerged at a far smaller size than expected from body size dimorphism. This led to higher workload, steeper wear rate and earlier depletion of male teeth than in females, in concordance with sex-specific patterns of lifetime performance and reproduction. These findings provide the empirical support for the disposable-soma hypothesis of senescence, which predicts that investment in bodily repair will decrease when the return from this investment may not be realized as a result of other causes that limit survival or reproduction.     

Insights into assembly from structural analysis of bacteriophage PRD1

The structure of the membrane-containing bacteriophage PRD1 has been determined by X-ray crystallography at about 4 A resolution. Here we describe the structure and location of proteins P3, P16, P30 and P31. Different structural proteins seem to have specialist roles in controlling virus assembly. The linearly extended P30 appears to nucleate the formation of the icosahedral facets (composed of trimers of the major capsid protein, P3) and acts as a molecular tape-measure, defining the size of the virus and cementing the facets together. Pentamers of P31 form the vertex base, interlocking with subunits of P3 and interacting with the membrane protein P16. The architectural similarities with adenovirus and one of the largest known virus particles PBCV-1 support the notion that the mechanism of assembly of PRD1 is scaleable and applies across the major viral lineage formed by these viruses.     

Tungsten isotope evidence that mantle plumes contain no contribution from the Earth's core

Osmium isotope ratios provide important constraints on the sources of ocean-island basalts, but two very different models have been put forward to explain such data. One model interprets (187)Os-enrichments in terms of a component of recycled oceanic crust within the source material. The other model infers that interaction of the mantle with the Earth's outer core produces the isotope anomalies and, as a result of coupled (186)Os-(187)Os anomalies, put time constraints on inner-core formation. Like osmium, tungsten is a siderophile ('iron-loving') element that preferentially partitioned into the Earth's core during core formation but is also 'incompatible' during mantle melting (it preferentially enters the melt phase), which makes it further depleted in the mantle. Tungsten should therefore be a sensitive tracer of core contributions in the source of mantle melts. Here we present high-precision tungsten isotope data from the same set of Hawaiian rocks used to establish the previously interpreted (186)Os-(187)Os anomalies and on selected South African rocks, which have also been proposed to contain a core contribution. None of the samples that we have analysed have a negative tungsten isotope value, as predicted from the core-contribution model. This rules out a simple core-mantle mixing scenario and suggests that the radiogenic osmium in ocean-island basalts can better be explained by the source of such basalts containing a component of recycled crust.     

Acylphosphatase overexpression triggers SH-SY5Y differentiation towards neuronal phenotype

An acylphosphatase (AcPase) overexpression study was carried out on SH-SY5Y neuroblastoma cells, using a green fluorescent fusion protein (AcP-GFP), with GFP acting as a reporter protein. The cellular proliferation rate was significantly reduced by overexpression of AcPase by a factor of ten. In contrast, clones transfected with two inactive AcPase mutants showed a growth rate comparable to control cells. This suggests that AcPase catalyzes the proliferative down-regulation. AcPase-overexpressing clones showed a physiological mortality rate as assessed by an MTT reduction test and by evaluation of necrotic markers. DNA fragmentation analysis and assays of caspase-3 and poly (ADP-ribose) polymerase (PARP)-active fragments showed no evidence of any apoptotic pattern. AcPase overexpression led to a marked increase in PARP activity as well as Bcl-2 content; these are commonly up-regulated during differentiative processes in neuronal cells. In fact, the typical differentiation marker, growth-associated-protein 43, was significantly up-regulated. Microscopic observations also showed a clear increase in the differentiative phenotype in AcPase-overexpressing cells. Our results clearly show that AcPase plays a primary causative role in neuronal differentiation.Received 3 May 2004; accepted 25 May 2004     

Strategies for the design of inhibitors of aldose reductase, an enzyme showing pronounced induced-fit adaptations

Aldose reductase is involved in the polyol pathway, catalyzing the reduction of glucose to sorbitol. However, due to pronounced binding site adaptations, the enzyme can operate on a broad palette of structurally diverse substrates ranging from small aliphatic and aromatic aldehydes up to steroid-type ligands. A comparative analysis of the presently accessible crystal structures of aldose reductase complexes reveals four binding-competent protein conformations. Additional relevant conformers are detected through molecular dynamics simulations. They indicate an equilibrium of several conformers which is shifted towards the binding-competent geometries upon ligand binding. Such a manifold system with several alternative binding site conformers requires some tailored concepts in virtual screening. We followed two strategies, both successfully suggesting new micromolar inhibitors. In a first attempt, we concentrated on one preferred conformer and performed a virtual screening, assuming that the binding pocket of aldose reductase adopts only this conformation. In a second approach, we followed a ligand superpositioning method. Ligands were extracted in their bound conformations from three different crystal structures, all accommodating the ligands with different active site conformations. After merging these ligands into one supermolecule, mutual alignments were computed, taking candidate ligands from a screening database. The latter strategy also retrieved several structurally new inhibitors of micromolar potency.