Letters in 2012

The authors show that p53 helps cancer cells survive serine depletion by coordinating metabolic remodelling; a diet lacking serine slowed tumour growth in mice, with p53-null tumours showing greatest sensitivity to serine starvation.

A new ultraluminous X-ray source has been discovered in M 31, whose variability and associated bright, compact radio emission identify it as a stellar-mass black hole accreting close to the Eddington limit.

Fluorescence of iron ions induced by an X-ray laser allows the relative oscillator strength for Fe xvii emission to be determined; it is found to differ by 3.6σ from the best quantum mechanical calculations, suggesting that the poor agreement between prediction and observations of the brightest Fe xvii line is rooted in the quality of the underlying atomic wavefunctions used in the models.

Climate models predict that precipitation will increase in Antarctica, leading to potential ice mass gain and an offset to sea level rise, but here it is shown that enhanced snowfall on Antarctica is likely to increase ice discharge and thereby negate 30% to 65% of the snowfall-induced ice gain.

A broadband, compact, all-electrically driven mid-infrared frequency comb based on a quantum cascade laser widens the scope of application of combs in this frequency range beyond that of sources which depend on a chain of optical components.

A morphological instability causing blobs of iron-rich liquid to penetrate iron oxides is described, providing a mechanism for the iron-rich regions in the mantle.

Biomarker and stable isotopic analysis of lipid residues from perforated pottery vessels from sixth millennium bc Europe are consistent with these vessels having been used for making cheese, a low-lactose dairy product with digestion and storage advantages for the prehistoric lactose-intolerant farming communities.

A new interpretation of fossilized soils (palaeosols) suggests that at least some Ediacaran (625–542 million years ago) organisms lived on land; thus these Ediacaran fossils were not animals, but a fungus-dominated terrestrial biota that predated vascular plants by about 100 million years.

Optogenetic induction of phasic, but not tonic, firing in VTA dopamine neurons induces susceptibility to stress in mice undergoing a subthreshold social-defeat paradigm and in previously resilient mice that have been subjected to repeated social-defeat stress, and this effect is projection-pathway specific.

A class of metal-free organic electroluminescent molecules is designed in which both singlet and triplet excitons contribute to light emission, leading to an intrinsic fluorescence efficiency greater than 90 per cent and an external electroluminescence efficiency comparable to that achieved in high-efficiency phosphorescence-based organic light-emitting diodes.

Airway epithelial cells are important in immune homeostasis in that they dampen immune activation by clearing dying cells and producing anti-inflammatory cytokines.

Single-molecule fluorescence microscopy techniques are used to elucidate features of the highly conserved protein-targeting machinery known as the signal recognition particle (SRP); the long SRP RNA is shown to be crucial for correct timing and precision of cargo handover to the protein-translocation machinery, a finding that could help to explain how other ribonucleosome complexes function during complex cellular processes.

Structural and functional analysis of the centralspindlin complex shows that it connects the mitotic spindle to the plasma membrane during cytokinesis through interactions of the C1 domain of centralspindlin’s MgcRacGAP subunit with phosphoinositide lipids.

Specific manipulation of midbrain dopamine neurons in freely moving rodents shows that their inhibition or excitation immediately modulates depression-like phenotypes that are induced by chronic mild stress, and that their activation alters the neural encoding of depression-related behaviours in the nucleus accumbens.

Mechanotransduction channels studied to date are mainly involved with sensing noxious mechanical stimuli; here NOMPC, a member of the TRP ion channel family, is identified as a pore-forming subunit of an ion channel essential to the sensation of gentle touch in Drosophila.

The crystal structure of the inner-membrane urea channel HpUreI from Helicobacter pylori, the causative organism of peptic ulcers, reveals how the channel selectively transports urea across the membrane and buffers the pathogen’s periplasmic pH against the acidic gastric environment.

TET2 is shown to associate with OGT, which catalyses O-GlcNAcylation, and the two enzymes are found together at transcription start sites; TET2 facilitates the activity of OGT in O-GlcNAcylation of histone 2B, and epigenetic modifications to both DNA and histones by TET2 and OGT may be important in gene transcription regulation.

Exposing a fused silica sample to a strong, waveform-controlled, few-cycle optical field increases the dielectric’s optical conductivity by more than 18 orders of magnitude in less than 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field.

Randomly adsorbing chemically synthesized silver nanocubes, each of which is the optical analogue of a grounded patch antenna, onto a nanoscale-thick polymer spacer layer on a gold film results in a metamaterial surface with a reflectance spectrum that can be tailored by varying the geometry.

An explanation for the formation of binary systems in which the components are extremely far apart is proposed: triple systems can break up and send one component far away by taking energy from the remaining binary, bringing the two stars so close together that from a distance they appear like one star.