Observed increase in local cooling effect of deforestation at higher latitudes

Deforestation in mid- to high latitudes is hypothesized to have the potential to cool the Earth's surface by altering biophysical processes. In climate models of continental-scale land clearing, the cooling is triggered by increases in surface albedo and is reinforced by a land albedo-sea ice feedback. This feedback is crucial in the model predictions; without it other biophysical processes may overwhelm the albedo effect to generate warming instead. Ongoing land-use activities, such as land management for climate mitigation, are occurring at local scales (hectares) presumably too small to generate the feedback, and it is not known whether the intrinsic biophysical mechanism on its own can change the surface temperature in a consistent manner. Nor has the effect of deforestation on climate been demonstrated over large areas from direct observations. Here we show that surface air temperature is lower in open land than in nearby forested land. The effect is 0.85 ± 0.44 K (mean ± one standard deviation) northwards of 45° N and 0.21 ± 0.53 K southwards. Below 35° N there is weak evidence that deforestation leads to warming. Results are based on comparisons of temperature at forested eddy covariance towers in the USA and Canada and, as a proxy for small areas of cleared land, nearby surface weather stations. Night-time temperature changes unrelated to changes in surface albedo are an important contributor to the overall cooling effect. The observed latitudinal dependence is consistent with theoretical expectation of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle, the latter of which remains uncertain in climate models.     

Frictional ageing from interfacial bonding and the origins of rate and state friction

Earthquakes have long been recognized as being the result of stick-slip frictional instabilities. Over the past few decades, laboratory studies of rock friction have elucidated many aspects of tectonic fault zone processes and earthquake phenomena. Typically, the static friction of rocks grows logarithmically with time when they are held in stationary contact, but the mechanism responsible for this strengthening is not understood. This time-dependent increase of frictional strength, or frictional ageing, is one manifestation of the 'evolution effect' in rate and state friction theory. A prevailing view is that the time dependence of rock friction results from increases in contact area caused by creep of contacting asperities. Here we present the results of atomic force microscopy experiments that instead show that frictional ageing arises from the formation of interfacial chemical bonds, and the large magnitude of ageing at the nanometre scale is quantitatively consistent with what is required to explain observations in macroscopic rock friction experiments. The relative magnitude of the evolution effect compared with that of the 'direct effect'--the dependence of friction on instantaneous changes in slip velocity--determine whether unstable slip, leading to earthquakes, is possible. Understanding the mechanism underlying the evolution effect would enable us to formulate physically based frictional constitutive laws, rather than the current empirically based 'laws', allowing more confident extrapolation to natural faults.     

Comprehensive analysis of the chromatin landscape in Drosophila melanogaster

Chromatin is composed of DNA and a variety of modified histones and non-histone proteins, which have an impact on cell differentiation, gene regulation and other key cellular processes. Here we present a genome-wide chromatin landscape for Drosophila melanogaster based on eighteen histone modifications, summarized by nine prevalent combinatorial patterns. Integrative analysis with other data (non-histone chromatin proteins, DNase I hypersensitivity, GRO-Seq reads produced by engaged polymerase, short/long RNA products) reveals discrete characteristics of chromosomes, genes, regulatory elements and other functional domains. We find that active genes display distinct chromatin signatures that are correlated with disparate gene lengths, exon patterns, regulatory functions and genomic contexts. We also demonstrate a diversity of signatures among Polycomb targets that include a subset with paused polymerase. This systematic profiling and integrative analysis of chromatin signatures provides insights into how genomic elements are regulated, and will serve as a resource for future experimental investigations of genome structure and function.     

Taxadiene synthase structure and evolution of modular architecture in terpene biosynthesis

With more than 55,000 members identified so far in all forms of life, the family of terpene or terpenoid natural products represents the epitome of molecular biodiversity. A well-known and important member of this family is the polycyclic diterpenoid Taxol (paclitaxel), which promotes tubulin polymerization and shows remarkable efficacy in cancer chemotherapy. The first committed step of Taxol biosynthesis in the Pacific yew (Taxus brevifolia) is the cyclization of the linear isoprenoid substrate geranylgeranyl diphosphate (GGPP) to form taxa-4(5),11(12)diene, which is catalysed by taxadiene synthase. The full-length form of this diterpene cyclase contains 862 residues, but a roughly 80-residue amino-terminal transit sequence is cleaved on maturation in plastids. We now report the X-ray crystal structure of a truncation variant lacking the transit sequence and an additional 27 residues at the N terminus, hereafter designated TXS. Specifically, we have determined structures of TXS complexed with 13-aza-13,14-dihydrocopalyl diphosphate (1.82?? resolution) and 2-fluorogeranylgeranyl diphosphate (2.25?? resolution). The TXS structure reveals a modular assembly of three α-helical domains. The carboxy-terminal catalytic domain is a class?I terpenoid cyclase, which binds and activates substrate GGPP with a three-metal ion cluster. The N-terminal domain and a third 'insertion' domain together adopt the fold of a vestigial class?II terpenoid cyclase. A class?II cyclase activates the isoprenoid substrate by protonation instead of ionization, and the TXS structure reveals a definitive connection between the two distinct cyclase classes in the evolution of terpenoid biosynthesis.     

Carbon loss from an unprecedented Arctic tundra wildfire

Arctic tundra soils store large amounts of carbon (C) in organic soil layers hundreds to thousands of years old that insulate, and in some cases maintain, permafrost soils. Fire has been largely absent from most of this biome since the early Holocene epoch, but its frequency and extent are increasing, probably in response to climate warming. The effect of fires on the C balance of tundra landscapes, however, remains largely unknown. The Anaktuvuk River fire in 2007 burned 1,039 square kilometres of Alaska's Arctic slope, making it the largest fire on record for the tundra biome and doubling the cumulative area burned since 1950 (ref. 5). Here we report that tundra ecosystems lost 2,016?±?435?g?C?m(-2) in the fire, an amount two orders of magnitude larger than annual net C exchange in undisturbed tundra. Sixty per cent of this C loss was from soil organic matter, and radiocarbon dating of residual soil layers revealed that the maximum age of soil C lost was 50 years. Scaled to the entire burned area, the fire released approximately 2.1?teragrams of C to the atmosphere, an amount similar in magnitude to the annual net C sink for the entire Arctic tundra biome averaged over the last quarter of the twentieth century. The magnitude of ecosystem C lost by fire, relative to both ecosystem and biome-scale fluxes, demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback, potentially offsetting Arctic greening and influencing the net C balance of the tundra biome.     

Corridors of migrating neurons in the human brain and their decline during infancy

The subventricular zone of many adult non-human mammals generates large numbers of new neurons destined for the olfactory bulb. Along the walls of the lateral ventricles, immature neuronal progeny migrate in tangentially oriented chains that coalesce into a rostral migratory stream (RMS) connecting the subventricular zone to the olfactory bulb. The adult human subventricular zone, in contrast, contains a hypocellular gap layer separating the ependymal lining from a periventricular ribbon of astrocytes. Some of these subventricular zone astrocytes can function as neural stem cells in vitro, but their function in vivo remains controversial. An initial report found few subventricular zone proliferating cells and rare migrating immature neurons in the RMS of adult humans. In contrast, a subsequent study indicated robust proliferation and migration in the human subventricular zone and RMS. Here we find that the infant human subventricular zone and RMS contain an extensive corridor of migrating immature neurons before 18 months of age but, contrary to previous reports, this germinal activity subsides in older children and is nearly extinct by adulthood. Surprisingly, during this limited window of neurogenesis, not all new neurons in the human subventricular zone are destined for the olfactory bulb--we describe a major migratory pathway that targets the prefrontal cortex in humans. Together, these findings reveal robust streams of tangentially migrating immature neurons in human early postnatal subventricular zone and cortex. These pathways represent potential targets of neurological injuries affecting neonates.     

A draft genome of Yersinia pestis from victims of the Black Death

Technological advances in DNA recovery and sequencing have drastically expanded the scope of genetic analyses of ancient specimens to the extent that full genomic investigations are now feasible and are quickly becoming standard. This trend has important implications for infectious disease research because genomic data from ancient microbes may help to elucidate mechanisms of pathogen evolution and adaptation for emerging and re-emerging infections. Here we report a reconstructed ancient genome of Yersinia pestis at 30-fold average coverage from Black Death victims securely dated to episodes of pestilence-associated mortality in London, England, 1348-1350. Genetic architecture and phylogenetic analysis indicate that the ancient organism is ancestral to most extant strains and sits very close to the ancestral node of all Y. pestis commonly associated with human infection. Temporal estimates suggest that the Black Death of 1347-1351 was the main historical event responsible for the introduction and widespread dissemination of the ancestor to all currently circulating Y. pestis strains pathogenic to humans, and further indicates that contemporary Y. pestis epidemics have their origins in the medieval era. Comparisons against modern genomes reveal no unique derived positions in the medieval organism, indicating that the perceived increased virulence of the disease during the Black Death may not have been due to bacterial phenotype. These findings support the notion that factors other than microbial genetics, such as environment, vector dynamics and host susceptibility, should be at the forefront of epidemiological discussions regarding emerging Y. pestis infections.     

In vivo genome editing restores haemostasis in a mouse model of haemophilia

Editing of the human genome to correct disease-causing mutations is a promising approach for the treatment of genetic disorders. Genome editing improves on simple gene-replacement strategies by effecting in situ correction of a mutant gene, thus restoring normal gene function under the control of endogenous regulatory elements and reducing risks associated with random insertion into the genome. Gene-specific targeting has historically been limited to mouse embryonic stem cells. The development of zinc finger nucleases (ZFNs) has permitted efficient genome editing in transformed and primary cells that were previously thought to be intractable to such genetic manipulation. In vitro, ZFNs have been shown to promote efficient genome editing via homology-directed repair by inducing a site-specific double-strand break (DSB) at a target locus, but it is unclear whether ZFNs can induce DSBs and stimulate genome editing at a clinically meaningful level in vivo. Here we show that ZFNs are able to induce DSBs efficiently when delivered directly to mouse liver and that, when co-delivered with an appropriately designed gene-targeting vector, they can stimulate gene replacement through both homology-directed and homology-independent targeted gene insertion at the ZFN-specified locus. The level of gene targeting achieved was sufficient to correct the prolonged clotting times in a mouse model of haemophilia B, and remained persistent after induced liver regeneration. Thus, ZFN-driven gene correction can be achieved in vivo, raising the possibility of genome editing as a viable strategy for the treatment of genetic disease.