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The cover shows a trackway and an isolated footprint (highlighted with charcoal) that were made by early four-legged land vertebrates (tetrapods) almost 400 million years ago. Thats 18 million years older than the earliest known tetrapod body fossils, and 10 million years older than the oldest elpistostegids Tiktaalik, Panderichthys and their relatives, seen as transitional forms between fishes and tetrapods. The hands on the right belong to Grzegorz Niedźwiedzki, first author of the paper reporting the finds. (CREDIT: Piotr Szrek)
An annual excursion to an exclusive Caribbean island has yielded an impressive body of ecological fieldwork. Just don't call it a holiday, says Mark Schrope.
For the first issue of the new decade, Nature asked a selection of leading researchers and policy-makers where their fields will be ten years from now. We invited them to identify the key questions their disciplines face, the major roadblocks and the pressing next steps.
The latest thesis on the disappearance of physicist Ettore Majorana adds little, but reminds us of the Nobel-prizewinning quality of the discoveries he made during his brief career, explains Frank Close.
The progenitors of type Ia supernovae, the standard candles that lit the way to dark energy, have been elusive. A largely dismissed scenario has now produced one, but the results aren't what anyone expected.
Retrieving a memory initiates a window of vulnerability for that memory. Simple behavioural methods can modify distressing memories during this window, eliminating fear reactions to traumatic reminders.
Retrieving a memory initiates a window of vulnerability for that memory. Simple behavioural methods can modify distressing memories during this window, eliminating fear reactions to traumatic reminders.
The peculiar ultra-fast trembling motion of a free electron — the Zitterbewegung predicted by Erwin Schrödinger in 1930 when he scrutinized the Dirac equation — has been simulated using a single trapped ion.
A survey of mammalian genomes has unexpectedly unearthed DNA derived from bornaviruses, leading to speculation about the role of these viruses in causing mutations with evolutionary and medical consequences.
The tracks left by organisms are among the most difficult of fossils to interpret. But just such evidence puts debate about the origins of four-limbed vertebrates (which include ourselves) on a changed footing.
The earliest body fossils of tetrapods (vertebrates with limbs rather than paired fins) date to the Late Devonian period. There have been claims of tetrapod trackways predating these body fossils but the age and identity of the track makers have remained controversial. The discovery of well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian age, around 18 million years older than the earliest tetrapod body fossils, is now presented.
During reconsolidation of memories, stored information is rendered labile after being retrieved and can be manipulated. Previous studies have used pharmacological intervention to disrupt retrieved memories; here, however, a non-invasive, behavioural technique is used to target the reconsolidation of fear memories in humans. Non-fearful information provided during the reconsolidation window appears to update old fear memories, causing a lack of expression of fear responses.
Although Archaea encode proteasomes highly related to those of eukaryotes, archaeal ubiquitin-like proteins are less conserved and not known to function in protein conjugation, complicating our understanding of the origins of ubiquitination. Two small archaeal modifier proteins, SAMP1 and SAMP2, structurally similar to ubiquitin, are now reported to form protein conjugates in the archaeon Haloferax volcanii.
Existing models of type Ia supernovae generally explain their observed properties, with the exception of the sub-luminous 1991bg-like supernovae. It has long been suspected that the merger of two white dwarfs could give rise to a type Ia event, but simulations so far have failed to produce an explosion. Here, a simulation of the merger of two equal-mass white dwarfs is presented that leads to a sub-luminous explosion; it requires a single common-envelope phase and component masses of about 0.9 solar masses.
The amplitude of the magnetic field near the Galactic Centre has been uncertain by two orders of magnitude for several decades. A compilation of previous data now reveals a downward break in the region's non-thermal radio spectrum; this requires that the Galactic Centre field be at least ∼50 microgauss on 400 parsec scales, with evidence supporting a field of 100 microgauss. This would imply that over 10% of the Galaxy's magnetic energy is contained in only around 0.05% (or less) of its volume.
The Dirac equation successfully merges quantum mechanics with special relativity. It predicts some peculiar effects such as 'Zitterbewegung', an unexpected quivering motion of a free relativistic quantum particle. This and other predicted phenomena are key fundamental examples for understanding relativistic quantum effects, but are difficult to observe in real particles. Here, using a single trapped ion set to behave as a free relativistic quantum particle, a quantum simulation of the one-dimensional Dirac equation is demonstrated.
Placing a macroscopic object in its quantum-mechanical ground state of motion is an exciting experimental target that should reveal counterintuitive physical behaviour — such as the existence of states in which the mechanical system is located in two places simultaneously. A nanomechanical resonator is now cooled to a point where the probability of its residing in the quantum ground state of motion is 0.21; this level of cooling should allow a series of fundamental quantum mechanical observations.
From earthquakes to hard drives, frictional motion and its strength are involved in a wide range of phenomena. The strength of an interface that divides two sliding bodies is determined by both the real contact area and the contacts' shear strength. By continuous measurements of the concurrent local evolution of the real contact area and the corresponding interface motion from the first microseconds when contact detachment occurs, frictional strength is now characterized from short to long timescales.
The Southern Ocean is potentially a substantial sink of anthropogenic carbon dioxide; however, the regulation of this carbon sink by the wind-driven Ekman flow, mesoscale eddies and their interaction is under debate. Here, a high-resolution ocean circulation and carbon cycle model is used to study intra-annual variability in anthropogenic carbon dioxide over a two-year time period; the Ekman flow is found to be the primary mechanism of anthropogenic carbon dioxide transport across the Antarctic polar front.
Until now, retroviruses have been the only group of viruses known to have left a fossil record, in the form of endogenous proviruses; those elements make up approximately 8% of the human genome. Elements homologous to the nucleoprotein gene of the non-retroviral bornavirus are now shown to exist in the genomes of several mammalian species; the results give insights into the role of bornavirus as a source of genetic novelty to its host.
The role of B-cell-receptor (BCR) signalling in human B cell lymphomas has been a long-standing question, with genetic and functional evidence for its oncogenic role in human lymphomas lacking. Here, a form of 'chronic active' BCR signalling that is required for cell survival in the activated B-cell-like subtype of diffuse large B-cell lymphoma is described and analysed, with potential implications for future therapeutic strategies.
Sister chromatids are generally assumed to be genetically and functionally identical, with segregation to daughter cells being a random process; however, some evidence contradicts both of these assumptions. A technique is now developed to observe chromatid segregation in mitotic cells in vivo. Whereas many sister chromatids appeared to be randomly distributed between daughter cells, non-random sister chromatid segregation is observed in a subset of cells.
If the activity of genetically specified neurons is silenced in a temporally precise fashion, the roles of different cell classes in neural processes can be studied. Members of the class of light-driven outward proton pumps are now shown to mediate powerful, safe, multiple-colour silencing of neural activity. The gene archaerhodopsin-3 (Arch) enables near 100% silencing of neurons in the awake brain when virally expressed in the mouse cortex and illuminated with yellow light.
MCL1 — essential for the survival of stem and progenitor cells of multiple lineages — is unique among pro-survival BCL2 family members in that it is rapidly turned over through the action of ubiquitin ligases. Abnormally high levels of MCL1 are expressed in some cancers, but the mechanism of MCL1 overexpression is not well understood. The deubiquitinase USP9X is now shown to stabilize MCL1 and thereby promote cell survival; this makes it a potential therapeutic target.
G-protein-coupled receptors (GPCRs) mediate the majority of cellular responses to hormones and neurotransmitters and are the largest group of therapeutic targets for a range of diseases. The extracellular surface (ECS) of GPCRs is diverse and therefore an ideal target for the discovery of subtype-selective drugs. Here, NMR spectroscopy is used to investigate ligand-specific conformational changes around a central structural feature in the ECS of a GPCR.
Kinase regulatory pathways are used in eukaryotic DNA replication to facilitate coordination with other processes during cell division cycles and response to environmental cues. The Dbf4–Cdc7 kinase (DDK) is one of at least two cell-cycle-regulated protein kinase systems essential for initiation of DNA replication. DDK is now shown to relieve the inhibitory activity of the amino-terminal domain of the replicative helicase Mcm4, thus promoting S phase.
If broken chromosomes arising from DNA double-strand breaks are left unrepaired or incorrectly repaired, they can lead to genomic changes that may result in cell death or cancer. DNA-dependent protein kinase (DNA-PK), which comprises the DNA-PK catalytic subunit (DNA-PKcs) and the heterodimer Ku70/Ku80, has a major role in the repair of double-strand breaks. The crystal structure of human DNA-PKcs is now presented, in which the overall fold is clearly visible.