Letters in 2014

Multiferroic devices that can switch magnetization with electric field at room temperature are desirable, but in BiFeO₃ the required direct 180-degree switch is thermodynamically forbidden; here it is shown that such switching is possible because the kinetics of the switching process favours a two-step sequence of partial switching.

Reconstruction of the Atlantic meridional overturning circulation from a highly resolved marine sedimentary record shows that a deep, vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, but that a shallower glacial mode prevailed during glacial maxima.

Seismicity and ground deformation measurements show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system in Iceland grew laterally for 45 kilometres over 14 days; dyke opening and seismicity were focused at the most distal segment, where lateral dyke growth with segment barrier breaking by pressure build-up occurred.

In Caenorhabditis elegans, reduced insulin/IGF-1 signalling can promote longevity through a program that is genetically distinct from the dauer developmental pathway, and requires SKN-1-dependent collagen remodelling that is a broadly essential feature of longevity assurance pathways.

The core promoters of developmental and housekeeping genes are shown to have distinct specificities for different enhancer sequences in Drosophila, and this specificity separates developmental and housekeeping gene regulatory programs across the genome.

Gas hydrates are ice-like solids that have guest species encaged within a crystalline water framework, making the empty hydrate a natural — though long assumed to be inaccessible — point of reference; it is now shown that several days of continuous vacuum pumping removes all guests from neon hydrate, and the physical properties of the empty hydrate have been determined.

A mechanical crack-based sensor inspired by the mechanism spiders use to sense minute variations in stress offers ultrahigh sensitivity to pressure and vibration and can easily be mounted on human skin for the purposes of speech recognition and the monitoring of physiological signals.

Analysis of air trapped in Antarctic ice between 16,000 and 10,000 years before present yields nitrous oxide concentrations and isotopic data showing that the relative contributions from marine and terrestrial sources to nitrous oxide emission changes were equal during that period, but that terrestrial emissions dominated on centennial timescales.

If deprived of exogenous glutamine, naive mouse embryonic stem cells are shown to be capable of generating the amino acid from other sources to enable their proliferation; the stem cells use glutamine and glucose catabolism to maintain a high level of intracellular α-ketoglutarate and promote demethylation of chromatin and ensure sufficient expression of pluripotency-associated genes.

Exome sequence analysis of nearly 10,000 people was carried out to identify alleles associated with early-onset myocardial infarction; mutations in low-density lipoprotein receptor (LDLR) or apolipoprotein A-V (APOA5) were associated with disease risk, identifying the key roles of low-density lipoprotein cholesterol and metabolism of triglyceride-rich lipoproteins.

The activation and coordination of phosphatase activity is important during mitotic exit; here, a mitotic phosphatase relay is described in fission yeast between the two major phosphatases, PP1 and PP2A, a mode of regulation that may be a feature of signalling networks across eukaryotes.

It has been traditionally assumed that the heat released during a single enzymatic catalytic event does not perturb the enzyme in any way; however, here single-molecule fluorescence correlation spectroscopy is used to show that, for enzymes that catalyse chemical reactions with large reaction enthalpies, the heat released at the protein's active site during catalysis transiently displaces the protein's centre-of-mass, essentially giving rise to a recoil effect that propels the enzyme.

Studies of gene-expression levels in embryos of Caenorhabditis elegans and of other phyla reveal the timing and location of expression of all genes and support a model in which the endoderm program dates back to the origin of multicellularity while the ectoderm originated as a secondary germ layer freed from ancestral feeding functions.

A tissue with many of the defining features of vertebrate cellular cartilage is shown to form transiently in larvae of the invertebrate chordate amphioxus, indicating that the origin of the vertebrate head skeleton depended not on evolution of a new skeletal tissue, as is commonly thought, but on the spread of this tissue throughout the head.

Wind tunnel experiments designed to simulate the conditions on Saturn’s moon Titan yield threshold wind speeds for particle saltation higher than those predicted by models derived from simulations of terrestrial-planet conditions; the results can be reconciled by modifying the models to take into account the low ratio of particle density to fluid density on Titan.

Somatic TP53 mutations are highly prevalent in therapy-related acute myeloid leukaemia and myelodysplastic syndrome, which arise as complications of cytotoxic chemotherapy or radiotherapy; although it was believed that these TP53 mutations are directly induced by cytotoxic therapy, new data indicate that they predate cytotoxic therapy and that haematopoietic progenitors harbouring these pre-existing mutations may selectively expand after exposure to chemotherapy or radiotherapy.

How socially transmitted behaviours spread and persist is shown in a wild animal population, revealing an effect of social conformity.

The deubiquitinase enzyme DUBA is shown to act as a negative regulator of interleukin-17A (IL-17A) in T_H17 cells; DUBA interacts with and stabilizes the ubiquitin ligase UBR5, which in turn targets RORγt for degradation in the proteaseome, thus limiting IL-17A production.

Using human bladder cancer xenograft models, a new mechanism involving an active proliferative response of cancer stem cells to chemotherapy-induced damage is shown, driven by prostaglandin E₂ (PGE₂) release in a manner similar to PGE₂-induced wound repair; pharmacological inhibition of the PGE₂/COX2 axis by celecoxib attenuates chemoresistance, suggesting a possible adjunctive therapy for bladder carcinomas.

Femtosecond X-ray diffraction and ab initio density functional theory calculations are used to determine the crystal structure of YBa₂Cu₃O_6.5 undergoing optically driven, nonlinear lattice excitation above the transition temperature of 52 kelvin, under which conditions the electronic structure of the material changes in such a way as to favour superconductivity.