Nitrogen loss in the oceans is a genuine puzzle still to be solved.
Voices within the Obama administration threaten to undermine non-proliferation efforts. They should be ignored.
Massive funding for Pakistan's ailing universities holds many lessons for other developing nations.
Barriers faced by foreign scientists seeking entry to the United States do more harm than good.
The Royal Society reviews options for fighting global warming with geoengineering.
Researchers describe the scientific and public-health challenges they face in battling the H1N1 virus.
Gene-synthesis industry at odds over how to screen DNA orders.
US science agencies may need to prove they are solving national problems. David Goldston explains.
Papers suggesting that biotech crops might harm the environment attract a hail of abuse from other scientists. Emily Waltz asks if the critics fight fair.
Lightning and fires on the Arctic tundra seem to be on the rise. Jane Qiu meets the researchers learning from the scorched earth in Alaska.
In 2002, Pakistan began an ambitious overhaul of its higher-education system. The successes and failures of the experience hold lessons for other countries, say Athar Osama and co-authors.
An adviser to US President Barack Obama argues that people's tendency to seek out those with similar views can entrench extreme opinions. But many other forces can fuel outlandish beliefs, says Herbert Gintis.
A retrospective of Todd Schorr's huge oil-painted comic-book visions features his garish image of a hunter-gatherer. Is it a deliberate allegory of consumer culture, asks Martin Kemp?
“Galaxies, like elephants, have long memories,” says an influential article from the 1980s. Tapping into these memories has revealed some surprising facts about the history of our neighbouring Andromeda galaxy.
Evidence linking metabolic alterations to cancer progression is accumulating. It seems that cancer cells must sustain their energy production and remain well fed to survive detachment from their normal habitat.
During her travels through Wonderland, Alice finds several ways of growing and shrinking in size. A polymeric vesicle plays the same trick in response to pH, in a process that might one day be useful for drug delivery.
Mechanosensitive channels release tension in cell membranes by opening 'pressure relief' pores. The structure of a partially open channel suggests a gating mechanism and delivers an unexpected architectural twist.
Reactive nitrogen is lost from the oceans as dinitrogen — N2 — produced by microbial metabolism. The latest twist in an ongoing story is that different pathways dominate in two of the oceanic regions concerned.
How does the brain remember the consequences of our actions? Persistent activity in the prefrontal cortex and basal ganglia may be crucial for learning correct actions through experience.
After transcription and processing, transfer RNAs must be exported from the nucleus to the cytoplasm, where translation occurs. This process is mediated by a dedicated nucleo-cytoplasmic transport factor called Xpot. Here, the structure of Schizosaccharomyces pombe Xpot is reported, unbound and in complex with both tRNA and another factor required for transport, RanGTP.
In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound and distant stars surrounding the galaxy. A panoramic survey of the Andromeda galaxy (M31) now reveals stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31.
Collisional redistribution of radiation has been proposed as a cooling mechanism for atomic two-level systems. Here, a proof-of-principle demonstration is reported in which a relative cooling of 66 K is achieved in an ultradense vapour of rubidium atoms and argon buffer gas. This technique may facilitate fundamental studies of supercooling and have applications in optical refrigeration.
Although we live in a macroscopic three-dimensional (3D) world, our best description of the structure of matter is at the atomic and molecular scale. Reconciling these two scales with atomic precision requires high spatial control of the 3D structure of matter, with the simplest practical route to achieving this being to form a crystalline arrangement by self-assembly. Here, the crystal structure of a designed, self-assembled 3D crystal based on the DNA tensegrity triangle is reported.
Fixed nitrogen availability limits primary production in over half of the world's oceans. Oceanic oxygen minimum zones (OMZs) are responsible for about 35% of oceanic dinitrogen gas (N2) production and up to half of that occurs in the Arabian Sea. It has recently been argued that anaerobic ammonia oxidation (anammox) alone is responsible for fixed nitrogen loss in the OMZs; however, here it is shown that denitrification rather than anammox dominates the N2 loss term in the Arabian Sea.
A key development in the history of technology was the transition to hand-axes and bifacial chopping tools during the Early Pleistocene (about 1.5 million years ago) in Africa. Puzzlingly, the earliest records in Europe of hand-axes lag behind this date by a million years, at around 0.5 million years ago. Here, palaeomagnetic analysis of two sites in southeastern Spain where hand-axes have been found yields revised dates of up to 0.9 million years ago, significantly closing the time gap.
Induced pluripotent stem (iPS) cells were first created by forced expression of four transcription factors in mouse fibroblasts, a technique that has since been widely used to generate embryonic stem (ES)-cell-like pluripotent cells from a variety of cell types in other species. The generation of several iPS cell lines in mice that are capable of generating viable, fertile live-born progeny by tetraploid complementation — a technique where chimaeric mice are generated using injected pluripotent cells — is now reported.
Differentiated cells can be reprogrammed into induced pluripotent stem (iPS) cells through the transient overexpression of a small number of transcription factors. These iPS cells resemble embryonic stem (ES) cells but, until now, they had not passed the most stringent test of pluripotency by generating full-term or adult mice in tetraploid complementation assays. Here, fertile adult mice derived entirely from iPS cells are reported.
The hearts of birds, mammals and crocodiles have two ventricles serving separate pulmonary and systemic circulations, whereas the hearts of amphibians have only one ventricle. In most reptiles, however, the situation is unclear, which is of interest in the context of the evolution of cardiac septation. Here, gene expression in the developing ventricles of two reptiles is analysed; the results suggest a role for the T-box transcription factor Tbx5.
The Rho GTPase family is involved in the control of cytoskeleton dynamics, but the spatiotemporal coordination of each element (Rac1, RhoA and Cdc42) remains unknown. Here, GTPase coordination in mouse embryonic fibroblasts is examined both through simultaneous visualization of two GTPase biosensors and using a computational approach.
The precise spatiotemporal dynamics of protein activity remain poorly understood, yet they can be critical in determining cell behaviour. A genetically encoded, photoactivatable version of the protein Rac1, a key GTPase regulating actin cytoskeletal dynamics, has now been produced; this approach enables the manipulation of the activity of Rac1 at precise times and places within a living cell, thus controlling motility.
Normal mammary epithelial cells require attachment to the extracellular matrix (ECM) for survival, but in breast cancers tumour cells acquire the ability to survive outside their natural ECM niches. Here it is found that cell detachment induces metabolic defects which can be rescued by both the expression of the oncogene ERBB2 and — unexpectedly — by antioxidants, which, in this context, help promote cancer cell survival and proliferation.
The ubiquitin ligase TRAF6 is essential for the activation of NF-κB and MAP kinases in several signalling pathways important for a range of cellular processes including immune function. TRAF6 functions together with a ubiquitin-conjugating enzyme complex to activate the TAK1 kinase complex downstream, which in turn leads to the activation of NF-κB. Here, by reconstituting TAK1 activation in vitro, free Lys 63 polyubiquitin chains are shown to activate TAK1 directly.
Mechanosensitive channels protect bacteria from osmotic shock by allowing ions to flow across the membrane in response to changes in membrane tension. MscL is one such channel with a large conductance. Although understanding of its closed and open states has been increasing, little is known about the structures of the important intermediate states. Here, the 3.8 Å crystal structure of MscL in what is probably a non-conductive, partially expanded intermediate state, is presented.
Kinesin is a dimeric motor protein which is known to move along microtubule filaments by using its twin motor domains (heads) to carry out an asymmetric, 'hand-over-hand' walk. However, the extent of individual head interactions with the microtubule has remained controversial. Here, a single-molecule assay is developed that can directly report head binding and unbinding during kinesin movement.
Visa problems continue to frustrate scientists seeking entry to the United States. Karen Kaplan investigates the roadblocks.