Volume 467 Issue 7311, 2 September 2010

Earth scientists have explained why Canada and South Africa are still here.

The week in science.

Fishing industry threatens to destabilize stocks.

Confounding reports seed confusion over long-term effects of the spill.

Extreme weather wreaks havoc in the rivers.

The US National Nanotechnology Initiative has spent billions of dollars on submicroscopic science in its first 10 years. Corie Lok finds out where the money went and what the initiative plans to do next.

When oil stopped gushing into the Gulf of Mexico, the ecosystems under assault started on a long road to recovery. Amanda Mascarelli meets the researchers assessing their chances.

Barack Obama is finding that sometimes politics needs to put science in its place, says Daniel Sarewitz.

The main consumer-targeted certification scheme for sustainable fisheries is failing to protect the environment and needs radical reform, say Jennifer Jacquet, Daniel Pauly and colleagues.

An ambitious atlas that charts the composition of frozen northern soils highlights their contribution to climate change, finds Philippe Ciais.

Theoretical models of the dynamics of self-driven systems predict the collective motion of biological systems, such as insect swarms. An experimental model has been developed to test the predictions.

A charitable deed by a few cells in a bacterial culture can help the rest of that population survive in the presence of antibiotics. This finding can aid further research into a major problem in public health.

The detection of water vapour in a carbon star has challenged the understanding of ageing stars. The discovery that such water can be warm shows that our knowledge of these objects is still rudimentary.

Presenilin proteins have a major role in normal cellular processes, but some contribute to disease, for example through the formation of amyloid-β. The way in which these different roles are regulated is now becoming clearer.

An optical device has been designed that performs a function exactly opposite to that of a laser. It perfectly absorbs incoming coherent radiation and turns it into thermal or electrical energy.

Scientists report the conversion of one type of differentiated cell, the fibroblast, into another — the cardiomyocyte. This approach may find use in regenerative strategies for the repair of damaged hearts.

Astronomer who discovered a new class of pulsar.

China has tremendous climatic and ecological diversity, so the impacts of climate change on natural and managed systems might likewise be expected to be diverse. Yet so far systematic studies have been rare. Here, the impacts of historical and future climate change on water resources and agriculture in China are assessed. Despite clear trends in climate, the overall impacts are overshadowed by natural variability and uncertainties in crop responses and projected climate, especially precipitation.

Here, the analysis of 'HapMap 3' is reported — a public data set of genomic variants in human populations. The resource integrates common and rare single nucleotide polymorphisms (SNPs) and copy number polymorphisms (CNPs) from 11 global populations, providing insights into population-specific differences among variants. It also demonstrates the feasibility of imputing newly discovered rare SNPs and CNPs.

Neurons of the peripheral nervous system need survival factors to prevent their death during development. Most in the central nervous system do not. Why are peripheral neurons so needy? Here it is shown that the neurotrophin receptors TrkA and TrkC, expressed at high levels by many peripheral nervous system neurons, behave as dependence receptors: they instruct neurons to die if there is no ligand around. By contrast, TrkB, expressed mainly in the central nervous system, does not signal death in the absence of ligand.

Water has been predicted to be almost absent in carbon-rich stars, so the detection of water vapour around the ageing carbon star IRC + 10216 challenged our understanding of the chemistry in old stars. Several explanations for the water have been postulated, but with only one water line detected it is difficult to discriminate between them. Now, dozens of water vapour lines have been detected in the far-infrared and sub-millimetre spectrum of IRC + 10216.

For several years, researchers have aspired to record in situ images of a quantum fluid in which each underlying quantum particle is detected. This goal has now been achieved: here, fluorescence imaging is reported of strongly interacting bosonic Mott insulators in an optical lattice, with single-atom and single-site resolution. The approach opens up new avenues for the manipulation, analysis and applications of strongly interacting quantum gases on a lattice.

Collective motion is a ubiquitous self-organization phenomenon that can be observed in systems ranging from flocks of animals to the cytoskeleton. Similarities between these systems suggest that there are universal underlying principles. This idea can be tested with 'active' or 'driven' fluids, but so far such systems have offered limited parameter control. Here, an active fluid is studied that contains only a few components — actin filaments and molecular motors — allowing the control of all relevant system parameters.

Cratons, the ancient cores of continents, extend laterally for hundreds of kilometres, and are underlain to depths of 180–250 km by mantle roots that are chemically and physically distinct from surrounding mantle. But how can these roots stay so isolated from mantle convection? Here it is shown that olivine in peridotite xenoliths from the lithosphere–athenosphere boundary region of the Kaapvaal craton mantle root is water-poor, providing sufficient viscosity contrast with the underlying asthenosphere to explain the root's stability.

Bacteria regularly evolve antibiotic resistance, but little is known about this process at the population level. Here, a continuous culture of Escherichia coli facing increasing antibiotic levels is followed. Most isolates taken from this population are less antibiotic resistant than the population as a whole. A few highly resistant mutants provide protection to the less resistant constituents, in part by producing the signalling molecule indole, which serves to turn on drug efflux pumps and oxidative-stress protective mechanisms.

One model for cancer development posits that the proliferating cells in a tumour can become 'addicted' to activating mutations in an oncogene. With the realization that certain microRNAs promote tumorigenesis, it has been proposed that tumours may also become dependent on such 'oncomiRs'. Here, evidence is provided that the gene encoding microRNA-21 is an oncogene, and that in its absence, tumours undergo apoptosis and regress. Thus tumours can indeed become addicted to oncomiRs.

The mitotic spindle plays a key part in determining the site of the cleavage furrow in dividing metazoan cells. But are other mechanisms also involved? Here evidence is provided for a spindle-independent pathway for furrow positioning that occurs during asymmetric divisions of Drosophila neuroblast cells. The pathway involves the Pins protein complex, which polarizes furrow-forming proteins to the basal cortex of the cell. This mechanism might also occur in other highly polarized cell types.

A major hallmark of Alzheimer's disease is the accumulation in the brain of amyloid-β peptide. This is generated by γ-secretase, which is thus of interest as a target for drugs to prevent amyloid-β accumulation. A problem is that γ-secretase has other substrates, including Notch, important in development. Here, a γ-secretase activating protein is identified that increases amyloid-β production without affecting Notch. Thus this protein can serve as an amyloid-β-lowering drug target without affecting other functions of γ-secretase.

The Na⁺/K⁺-ATPase pumps three sodium ions out of and two potassium ions into the cell while splitting a single molecule of ATP. Here it is found that the carboxy terminus of the ATPase's α-subunit is also a key regulator of a previously unrecognized ion pathway. The data indicate that, in the ATPase's potassium-bound state, a cytoplasmic proton can enter and stabilize site III when empty. When potassium is released, the proton returns to the cytoplasm, thus permitting an overall asymmetric stoichiometry of the transported ions.

Experimental determination of the secondary structure of RNA molecules has usually been carried out on a case-by-case basis. Now, however, a deep-sequencing approach has been used to profile the secondary structure of 3,000 distinct messenger RNA transcripts from Saccharomyces cerevisiae. The results provide interesting hints about the role of secondary structure in protein translation, and set the stage for the examination of how such structures can change in response to environmental conditions.

When double-strand breaks occur in DNA, the broken ends must undergo processing to prepare them for repair. Here, and in an accompanying study, this processing reaction has now been replicated in vitro using yeast proteins. Processing minimally requires the activities of a helicase, a nuclease and a single-strand-binding protein, although the reaction is enhanced by the addition of three factors that help to target the core complex and stimulate the unwinding activity.

When double-strand breaks occur in DNA, the broken ends must undergo processing to prepare them for repair. Here, and in an accompanying study, this processing reaction has now been replicated in vitro using yeast proteins. Processing minimally requires the activities of a helicase, a nuclease and a single-strand-binding protein, although the reaction is enhanced by the addition of three factors that help to target the core complex and stimulate the unwinding activity.

Fekrije Selimi, a neurobiologist at the National Center for Scientific Research in Paris, received the Boehringer Ingelheim Federation of European Neurosciences award in July. She tells Nature how she embraces career challenges.

Postdoctoral programme pays double the average annual stipend.

University of California students join forces and negotiate.

Admission offers to students from China rise by 16%.

Choosing a postdoc doesn't just mean finding the right research programme. Jeffrey Perkel looks at the other factors to consider.

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