Enhanced virulence of influenza A viruses with the haemagglutinin of the 1918 pandemic virus

The 'Spanish' influenza pandemic of 1918-19 was the most devastating outbreak of infectious disease in recorded history. At least 20 million people died from their illness, which was characterized by an unusually severe and rapid clinical course. The complete sequencing of several genes of the 1918 influenza virus has made it possible to study the functions of the proteins encoded by these genes in viruses generated by reverse genetics, a technique that permits the generation of infectious viruses entirely from cloned complementary DNA. Thus, to identify properties of the 1918 pandemic influenza A strain that might be related to its extraordinary virulence, viruses were produced containing the viral haemagglutinin (HA) and neuraminidase (NA) genes of the 1918 strain. The HA of this strain supports the pathogenicity of a mouse-adapted virus in this animal. Here we demonstrate that the HA of the 1918 virus confers enhanced pathogenicity in mice to recent human viruses that are otherwise non-pathogenic in this host. Moreover, these highly virulent recombinant viruses expressing the 1918 viral HA could infect the entire lung and induce high levels of macrophage-derived chemokines and cytokines, which resulted in infiltration of inflammatory cells and severe haemorrhage, hallmarks of the illness produced during the original pandemic.     

Cytoplasmic dynein functions as a gear in response to load

Cytoskeletal molecular motors belonging to the kinesin and dynein families transport cargos (for example, messenger RNA, endosomes, virus) on polymerized linear structures called microtubules in the cell. These 'nanomachines' use energy obtained from ATP hydrolysis to generate force, and move in a step-like manner on microtubules. Dynein has a complex and fundamentally different structure from other motor families. Thus, understanding dynein's force generation can yield new insight into the architecture and function of nanomachines. Here, we use an optical trap to quantify motion of polystyrene beads driven along microtubules by single cytoplasmic dynein motors. Under no load, dynein moves predominantly with a mixture of 24-nm and 32-nm steps. When moving against load applied by an optical trap, dynein can decrease step size to 8 nm and produce force up to 1.1 pN. This correlation between step size and force production is consistent with a molecular gear mechanism. The ability to take smaller but more powerful strokes under load--that is, to shift gears--depends on the availability of ATP. We propose a model whereby the gear is downshifted through load-induced binding of ATP at secondary sites in the dynein head.     

Hedgehog signalling in prostate regeneration, neoplasia and metastasis

Metastatic cancers adopt certain properties of normal cells in developing or regenerating organs, such as the ability to proliferate and alter tissue organization. We find here that activity of the Hedgehog (Hh) signalling pathway, which has essential roles in developmental patterning, is required for regeneration of prostate epithelium, and that continuous pathway activation transforms prostate progenitor cells and renders them tumorigenic. Elevated pathway activity furthermore distinguishes metastatic from localized prostate cancer, and pathway manipulation can modulate invasiveness and metastasis. Pathway activity is triggered in response to endogenous expression of Hh ligands, and is dependent upon the expression of Smoothened, an essential Hh response component that is not expressed in benign prostate epithelial cells. Monitoring and manipulating Hh pathway activity may thus offer significant improvements in diagnosis and treatment of prostate cancers with metastatic potential.     

Millennial and orbital variations of El Niño/Southern Oscillation and high-latitude climate in the last glacial period

The El Ni?o/Southern Oscillation (ENSO) phenomenon is believed to have operated continuously over the last glacial-interglacial cycle. ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time, but the proposals disagree on whether increased frequency of El Ni?o events, the warm phase of ENSO, was linked to North Atlantic warm or cold periods. Here we present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges to grass, from northern Queensland, Australia, covering the past 45,000 yr. We observe millennial-scale dry periods, indicating periods of frequent El Ni?o events (summer precipitation declines in El Ni?o years in northeastern Australia). We find that these dry periods are correlated to the Dansgaard-Oeschger events--millennial-scale warm events in the North Atlantic climate record--although no direct atmospheric connection from the North Atlantic to our site can be invoked. Additionally, we find climatic cycles at a semiprecessional timescale (approximately 11,900 yr). We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales, which determined precipitation in northeastern Australia, also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections.     

Determinants of woody cover in African savannas

Savannas are globally important ecosystems of great significance to human economies. In these biomes, which are characterized by the co-dominance of trees and grasses, woody cover is a chief determinant of ecosystem properties. The availability of resources (water, nutrients) and disturbance regimes (fire, herbivory) are thought to be important in regulating woody cover, but perceptions differ on which of these are the primary drivers of savanna structure. Here we show, using data from 854 sites across Africa, that maximum woody cover in savannas receiving a mean annual precipitation (MAP) of less than approximately 650 mm is constrained by, and increases linearly with, MAP. These arid and semi-arid savannas may be considered 'stable' systems in which water constrains woody cover and permits grasses to coexist, while fire, herbivory and soil properties interact to reduce woody cover below the MAP-controlled upper bound. Above a MAP of approximately 650 mm, savannas are 'unstable' systems in which MAP is sufficient for woody canopy closure, and disturbances (fire, herbivory) are required for the coexistence of trees and grass. These results provide insights into the nature of African savannas and suggest that future changes in precipitation may considerably affect their distribution and dynamics.     

Doping semiconductor nanocrystals

Doping--the intentional introduction of impurities into a material--is fundamental to controlling the properties of bulk semiconductors. This has stimulated similar efforts to dope semiconductor nanocrystals. Despite some successes, many of these efforts have failed, for reasons that remain unclear. For example, Mn can be incorporated into nanocrystals of CdS and ZnSe (refs 7-9), but not into CdSe (ref. 12)--despite comparable bulk solubilities of near 50 per cent. These difficulties, which have hindered development of new nanocrystalline materials, are often attributed to 'self-purification', an allegedly intrinsic mechanism whereby impurities are expelled. Here we show instead that the underlying mechanism that controls doping is the initial adsorption of impurities on the nanocrystal surface during growth. We find that adsorption--and therefore doping efficiency--is determined by three main factors: surface morphology, nanocrystal shape, and surfactants in the growth solution. Calculated Mn adsorption energies and equilibrium shapes for several nanocrystals lead to specific doping predictions. These are confirmed by measuring how the Mn concentration in ZnSe varies with nanocrystal size and shape. Finally, we use our predictions to incorporate Mn into previously undopable CdSe nanocrystals. This success establishes that earlier difficulties with doping are not intrinsic, and suggests that a variety of doped nanocrystals--for applications from solar cells to spintronics--can be anticipated.     

Geophysics: a moving fluid pulse in a fault zone

In the Gulf of Mexico, fault zones are linked with a complex and dynamic system of plumbing in the Earth's subsurface. Here we use time-lapse seismic-reflection imaging to reveal a pulse of fluid ascending rapidly inside one of these fault zones. Such intermittent fault 'burping' is likely to be an important factor in the migration of subsurface hydrocarbons.     

Large-scale sequencing of human influenza reveals the dynamic nature of viral genome evolution

Influenza viruses are remarkably adept at surviving in the human population over a long timescale. The human influenza A virus continues to thrive even among populations with widespread access to vaccines, and continues to be a major cause of morbidity and mortality. The virus mutates from year to year, making the existing vaccines ineffective on a regular basis, and requiring that new strains be chosen for a new vaccine. Less-frequent major changes, known as antigenic shift, create new strains against which the human population has little protective immunity, thereby causing worldwide pandemics. The most recent pandemics include the 1918 'Spanish' flu, one of the most deadly outbreaks in recorded history, which killed 30-50 million people worldwide, the 1957 'Asian' flu, and the 1968 'Hong Kong' flu. Motivated by the need for a better understanding of influenza evolution, we have developed flexible protocols that make it possible to apply large-scale sequencing techniques to the highly variable influenza genome. Here we report the results of sequencing 209 complete genomes of the human influenza A virus, encompassing a total of 2,821,103 nucleotides. In addition to increasing markedly the number of publicly available, complete influenza virus genomes, we have discovered several anomalies in these first 209 genomes that demonstrate the dynamic nature of influenza transmission and evolution. This new, large-scale sequencing effort promises to provide a more comprehensive picture of the evolution of influenza viruses and of their pattern of transmission through human and animal populations. All data from this project are being deposited, without delay, in public archives.     

Gains of glycosylation comprise an unexpectedly large group of pathogenic mutations

Mutations involving gains of glycosylation have been considered rare, and the pathogenic role of the new carbohydrate chains has never been formally established. We identified three children with mendelian susceptibility to mycobacterial disease who were homozygous with respect to a missense mutation in IFNGR2 creating a new N-glycosylation site in the IFNgammaR2 chain. The resulting additional carbohydrate moiety was both necessary and sufficient to abolish the cellular response to IFNgamma. We then searched the Human Gene Mutation Database for potential gain-of-N-glycosylation missense mutations; of 10,047 mutations in 577 genes encoding proteins trafficked through the secretory pathway, we identified 142 candidate mutations ( approximately 1.4%) in 77 genes ( approximately 13.3%). Six mutant proteins bore new N-linked carbohydrate moieties. Thus, an unexpectedly high proportion of mutations that cause human genetic disease might lead to the creation of new N-glycosylation sites. Their pathogenic effects may be a direct consequence of the addition of N-linked carbohydrate.