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Genetic screening reveals that most Indians today can trace their ancestry back to two ancient, genetically divergent populations. One lineage, Ancestral North Indian, is genetically close to Middle Easterners, Central Asians and Europeans. The other, Ancestral South Indian, is not close to any group outside the subcontinent. The cover image (by Kumarasamy Thangaraj, Lalji Singh & Francis Amirtharaj) shows the locations of the 25 diverse groups sampled for the genetic screen, and a member of each group.
Canada's Perimeter Institute of Theoretical Physics was intended to become a world leader in the field. Eric Hand finds out if it has lived up to its ambitions.
Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockström and colleagues.
Frank Oppenheimer founded the San Francisco Exploratorium: his charisma and passion for science education made him as influential, if not as famous, as his brother, explains Robert Crease.
Past societies have struggled against environmental problems similar to those that beset us today. Three publications illuminate the outcomes for three different tropical civilizations during the period AD 700–1600.
Gradients of signalling molecules dictate where specific cell types form in developing tissues, but how these gradients are set up is much debated. A model proposed 40 years ago by Francis Crick may provide an answer.
Patterns of sea-surface warming and cooling in the tropical Pacific seem to be changing, as do the associated atmospheric effects. Increased global warming is implicated in these shifts in El Niño phenomena.
A crystal structure reveals how a protein kinase is activated by the binding of a small molecule at a pocket far from the catalytic site. This opens the door to the design of modulators of protein phosphorylation.
By borrowing a technique used by seismologists to investigate Earth's interior, astronomers have probed the hitherto-unknown interior rotation profile of a white-dwarf star.
Reactive oxygen species are often blamed for the development of cancer and other diseases. Contrary to their 'bad boy' reputation, these species seem to be essential for the development of immune cells, at least in the fly.
One measure of the extraordinary level of human diversity found in India is the use of 15 languages on its banknotes. The genetic underpinnings of that population diversity are yielding to whole-genome analysis.
Genome-wide analysis of human variation in 25 diverse groups from India reveals two ancient populations, genetically divergent, that are ancestral to most Indians today. Traditionally upper caste and Indo-European speakers tend to be descended from a group that is genetically close to Middle Easterners, Central Asians and Europeans. The other group, the 'Ancestral South Indians', does not appear to be close to any group outside the subcontinent.
A known regulator of prostate epithelial differentiation, Nkx3-1, is shown here to mark a stem cell population that functions during prostate regeneration. Furthermore, in mice in which the Pten tumour suppressor gene is deleted in a group of rare cells that express Nkx3-1 in the absence of testicular androgens, termed CARN cells, there is rapid carcinoma formation after andogen-mediated regeneration. These observations indicate that prostate cancer can originate in CARN cells.
The majority of all stars finish their evolution as white dwarf stars. If white dwarf stars kept the angular momentum of their progenitors, they should rotate relatively rapidly, with typical periods of the order of a few seconds. Observations show that they rotate much more slowly, but it is not known whether a white dwarf could 'hide' some of its original angular momentum below its superficial layers. Here, a determination of the internal rotation profile of a white dwarf shows that it rotates as a solid body and with a relatively long period.
Bell inequalities are a quantitative measure that can distinguish classically determined correlations from stronger quantum correlations, and their measurement provides strong experimental evidence that quantum mechanics provides a complete description. The violation of a Bell inequality is now demonstrated in a solid-state system; the experiment provides further strong evidence that a macroscopic electrical circuit is really a quantum system.
Antarctic ice cores can be used to reconstruct atmospheric CO2 concentrations, revealing significant changes during the Holocene epoch which started 11,000 years ago. Here, a highly resolved δ13C record is presented for the past 11,000 years from measurements on atmospheric CO2 trapped in an Antarctic ice core. These data are combined with a simplified carbon cycle model to shed light on the processes responsible for the changes in CO2 concentrations.
A distinctly different type of El Niño event, causing global climate effects dramatically different from those caused by the canonical El Niño, was observed in the late twentieth century. Using data from projected global warming scenarios it is now demonstrated that this new type of El Niño event is likely to become progressively more common in the future as a result of anthropogenic climate change.
Whether evolution can go back to an ancestral structure by reversing the selection pressure on function has long fascinated biologists. Here, the evolution of hormone specificity in the vertebrate glucocorticoid receptor is used as a case-study to investigate this issue; the mutations that optimized the new specificity of the glucocorticoid receptor are found to have destabilized elements of the protein structure that were required to support the ancestral conformation.
Susceptibility to drug treatment or viral infection can vary greatly from one cell to another even in a population of genetically identical cells cultured together, but until now the causes of this heterogeneity had not been investigated. Here, deterministic links are revealed between fundamental cellular features and a cell's population context — for example, whether a cell is localized at the centre or at the periphery of an island of adhering cells.
During development of the cerebral cortex, excitatory projection neurons migrate to form a cellular infrastructure of radial columns. However, some of these clonally related neurons undergo a lateral shift to intermix with neurons originating from neighbouring proliferative units. This process is now shown to be dependent on Eph receptor A and ephrin A signalling, a so far unrecognized mechanism for lateral neuronal dispersion that seems to be essential for the proper intermixing of neuronal types in the cortical columns.
Infectious prion diseases are transmitted naturally within affected host populations, for example of sheep and deer. Once an animal is symptomatic its excretions may contain contagious prions, but the biological importance of these sources in sustaining epidemics remains unclear. Here it is shown that asymptomatic mule deer infected with chronic wasting disease excrete infectious prions in their faeces long before they develop clinical signs of prion disease.
Concentration gradients of certain molecules termed 'morphogens' are known to control tissue development during embryogenesis, but how exactly these gradients are formed remains unclear. Using the technique of fluorescence correlation spectroscopy, Fgf8 morphogen gradients are now shown to be established and maintained in living zebrafish by two essential factors: free diffusion of single molecules away from the source and a sink function of the receiving cells.
Reactive oxygen species (ROS) are generally considered to be deleterious to cells. Despite the fact that, in mammals, haematopoietic stem cells contain low levels of ROS, common myeloid progenitors (CMPs) unexpectedly produce relatively high levels of ROS. Here it is shown that the equivalent class of cells to CMPs in Drosophila display increased levels of ROS in vivo, apparently priming them for differentiation.
Activation of the kinase RAF, a member of the ERK (extracellular signal-regulated kinase) pathway, is triggered by the binding of growth factors to receptor tyrosine kinases. Activating mutations in RAF can lead to unbridled signalling through the ERK pathway and have been linked to several human cancers. Here, the activation mechanism of RAF is shown to involve a specific mode of dimerization of its kinase domain, which is relevant for the action of the RAF activator KSR and certain oncogenic mutations.
MicroRNAs have important roles in shaping gene expression profiles during development, repressing target messenger RNAs to control various biological processes. The degradation of mature microRNAs in the nematode Caenorhabditis elegans, mediated by the 5′→3′ exoribonuclease XRN-2, is now found to affect functional microRNA homeostasis in vivo.
Biotechnology and drug companies are piquing graduate student interest with goal-oriented postdoctoral fellowships that maintain academic ties. Karen Kaplan surveys the offerings.