This Week in Science

Science  07 Nov 2008:
Vol. 322, Issue 5903, pp. 817
  1. Tales of the Asian Monsoon


    The Asian Monsoon is important for climate because it transports large amounts of heat and moisture from the ocean to the land. The monsoon is also important for human settlement because agriculture depends on monsoon rainwater. Using a record derived from a Chinese stalagmite, Zhang et al. (p. 940) present a detailed history of the Asian Monsoon over the past 1800 years that indicates connections between the monsoon, solar irradiation, Northern Hemispheric temperature, and glacial cycles in Europe. Shifts in the strength of the monsoon also correlate with the succession of Chinese dynasties, underscoring the importance that climate can have on human societies.

  2. Stem Cells on Demand

    Infection of adult mouse cells with viruses expressing genes of four transcription factors (Oct4, Sox2, c-myc, and Klf4) generates pluripotent stem cells (iPS) that resemble embryonic stem cells. Viruses commonly used for this procedure permanently alter the cells' genome and can cause tumors in animals, and thus these iPS cells cannot be used directly for cell therapy. Stadtfeld et al. (p. 945, published online 25 September) have produced mouse iPS cells by transiently exposing adult skin and liver cells to the four transcription factor genes using adenoviruses (that generally do not integrate into the genome). Thus, it is possible to make iPS cells without permanent genetic manipulation and it should be possible to make patient-specific cells not only to study disease but also for the future use of iPS cells in a clinical setting.

  3. Sheltering Excitons in Quantum Dots


    Quantum dots can exhibit long-lived fluorescence, but their excitonic states, which potentially are useful in photovoltaic and infrared detection applications, tend to decay very rapidly (in less than 1 picosecond). Pandey and Guyot-Sionnest (p. 929) report that the cooling of the two lowest energy excited states in cadmium-selenium quantum dots can be slowed by a thick coating of an electron insulator, in this case zinc-selenium. By using such insulation, the lifetimes of the excitonic states were extended to more than a nanosecond.

  4. Going for the Burn

    Fitness classes promote the idea that burning fat makes people healthier and perhaps live longer. Wang et al. (p. 957; see the Perspective by Xie) find that the Caenorhabditis elegans roundworm also adopts a fat-burning strategy to help them extend life. Up-regulation of a specific lipase, K04A8.5, decreases fat storage and increases lifespan. The lipase level is low during adulthood but can be induced 10-fold when germline stem cells stop proliferating. In addition, the lipase contributes to longevity in worms by reducing insulin signaling. Thus, at least in C. elegans, fat metabolism and life-span control are directly linked.

  5. Himalayan Graphite

    Earth has an oxygen-rich atmosphere because, on a geological time scale, more organic material is created by photosynthesis than is respired back to carbon dioxide. Thus, knowing the particulars of how organic carbon is transformed by various geological processes, such as mountain-building, is essential for understanding the carbon and oxygen cycles. Galy et al. (p. 943) report that organic carbon is converted with surprising efficiency to graphite in the Himalayas, and subsequently buried in marine sediments after fluvial transport. During the erosion cycle up to half the carbon in the rocks was turned into graphite and sequestered in sediments, suggesting that the process could operate on a global scale to control carbon and oxygen cycles.

  6. Moving Memories

    The earliest phases of memory acquisition rely on the hippocampus, but growing evidence suggests that another area in the brain called the medial prefrontal cortex may take over in consolidated associative memories. Takehara-Nishiuchi and McNaughton (p. 960) found that following acquisition of an associative memory, neuronal activity in the rat medial prefrontal cortex became specific and necessary for the acquired memory. Selective activity patterns developed spontaneously during a consolidation period of about 6 weeks even without repetitive conditionings. Thus, a neural correlate of the memory gradually develops in the neocortex simultaneously with memory consolidation.

  7. Mantle Flow

    Seismic data provide an image of Earth's mantle today. Geologic data from mountain belts or sedimentary records in basins record the overall effects of mantle flow, but may not reveal the actual flow patterns. Starting with these observations, plus estimates of mantle properties, Liu et al. (p. 934; see the Perspective by Steinberger) have developed a model of the evolution of western North America during the past 100 million years. The model is consistent with flat subduction of the Farallon oceanic plate beneath the continent during much of this time, but shallow subduction extended over a larger area, which could explain a broad Cretaceous unconformity in sedimentary records.

  8. Dry as a Bone Moon

    Radar observations of the Moon from the Clementine spacecraft indicated water ice is present in the permanently shadowed Shackleton crater at the south pole. However, this finding has not been confirmed by Earth-based radar. Using a camera on board the SELENE (Kaguya) spacecraft, now orbiting the moon, Haruyama et al. (p. 938) have been able to peer into this crater, and using the faint light reflected off the crater walls have measured the albedo and estimated surface temperatures across the interior. Although sufficiently cold (about 90 kelvin), the crater apparently lacks any large expanse of exposed ice. It is still possible that there are small amounts of ice beneath the surface, or mixed in the surface dust.

  9. More Stem Cells on Demand

    To rule out any risk of viral vectors integrating into the host genome and causing tumors, Okita et al. (p. 949, published online 9 October) used a plasmid transfection procedure to introduce transcription factor genes into mouse embryonic fibroblasts to make pluripotent cells. These cells show many features of embryonic stem cells, including the expression of pluripotency markers, as well as the capacity to develop teratomas and chimeras when transplanted into mice. Importantly, there was no evidence of plasmid integration and, although less efficient than other methods, this method looks like it will offer a safer way of inducing pluripotent stem cells.

  10. Processing Speech and Voice


    In everyday life, we automatically and effortlessly decode speech into language independently of who speaks. Similarly, we recognize a speaker's voice independently of what he says. Formisano et al. (p. 970) show that it is possible to decode the contents of speech and the identity of the speaker from measurements of the brain activity of a listener. They map and decode, trial-by-trial, the spatially distributed activation patterns evoked by listening to different vowels or speakers evoke in distinct patches of the listeners' auditory cortex. The pattern associated with a vowel does not change if the vowel is spoken by another speaker and the pattern associated with a speaker does not depend on what the person says.

  11. Brain Repair

    In mammals, a severed nerve in an arm or leg will eventually regrow and reestablish functional connections. A similar injury in the spinal cord or within the brain will not be repaired, resulting in permanent disability and paralysis. Poor regeneration in the central nervous system has been attributed to proteins embedded in brain myelin (the membranes that wrap each nerve axon), which interact with an inhibitory receptor on neurons called NgR. Two papers in this issue show that other inhibitory receptors recognize the myelin-embedded proteins (see the Perspective by Kim and Snider). Atwal et al. (p. 967) identified PirB, a mouse protein related to the immunoglobulins of the immune system, and if both PirB and NgR were blocked, regeneration resumed. Park et al. (p. 963) found that after injury to the optic nerve, the axons of the retinal ganglion cells in mice will regenerate if the growth-related signaling pathway mTOR is activated in these cells. When negative regulators of the mTOR pathway were deleted in the retinas of mice, within a few weeks, the axons of retinal ganglion cells would re-grow as far as the optic chiasm. Thus, to promote recovery from neural damage, a combination of therapeutic approaches is needed to remove inhibitory processes, as well as to stimulate the intrinsic growth pathways of the neurons.

  12. Not Quite Sleep

    Although thousands of people are made unresponsive under anesthesia, they are not always rendered unconscious, and stories of waking, eviscerated, on the operating table abound. Alkire et al. (p. 876) review what little we do know about the gap between behavioral unresponsiveness and oblivion. Although the relative role of the thalamus and cortical areas in switching consciousness on and off is not clear, despite their different mechanisms of action it does seem that most anesthetics hit a posterior corticothalamic complex centered around the inferior parietal lobe. As well as deactivating this region, anesthesia also causes functional disconnection between subregions of the complex. Understanding the effects of anesthesia could thus be a useful tool to understanding the neural correlates of consciousness.

  13. Ins and Outs of Bimetallic Nanoparticles

    Heterogeneous catalysts that alloy two metals may undergo changes in the distribution of the metals between the surface and the interior as the reaction conditions change from oxidizing to reducing. Tao et al. (p. 932, published online 9 October) synthesized nanoparticles with equal fractions of either rhodium (Rh) and palladium (Pd) or platinum (Pt) and Pd, deposited them on a silicon wafer support, and then analyzed changes in surface composition via x-ray photoelectron spectroscopy after exposure to various gases (nitric oxide, carbon monoxide, oxygen, and hydrogen) at pressures approaching hundreds of Pascals. Although the Pt-Pd nanoparticles showed no changes in surface composition, the surfaces of the Rh-Pd nanoparticles became enriched with Rh under oxidizing conditions and Pd-enriched under reducing conditions. These results suggest that changes in reactant-induced changes surface composition may be a tunable parameter to consider in developing new catalysts.

  14. Protein Lifetimes

    Advances in microarray technologies have focused attention on the regulation of cellular processes by transcriptional control mechanisms. But translation and regulated protein degradation can be equally important parameters in determining physiological effects of proteins (see the Perspective by Grabbe and Dikic). Yen et al. (p. 918) and Yen and Elledge (p. 923) have monitored the lifetime of thousands of individual proteins under various physiological or pathological conditions that can be reproduced in cell culture. The trick is to use a reporter construct having a single promoter that encodes two protein transcripts produced in equal amounts. One is red fluorescent protein and the second is the protein (whose stability you want to know) tagged with a green fluorescent label. The red fluorescent protein is stable and thus the ratio of fluorescence of the two proteins gives a measure of the stability of the protein being examined. Fluorescence-activated cell sorting is used to separate cells bearing proteins of a particular half-life, and the encoding genes carried in the cells are then identified by the polymerase chain reaction. The method has identified previously unrecognized substrates for E3 ubiquitin ligases, which function in control of processes including the cell division cycle, cellular signaling, and apoptosis.

  15. Stop Translation Now

    To terminate translation, a protein release factor recognizes the stop codon on messenger RNA and catalyzes hydrolysis of the nascent protein chain from transfer RNA bound to the ribosome. In bacteria, there are two release factors that have overlapping specificity for the three stop codons—RF1 recognizes UAG, while RF2 recognizes UGA, and both recognize UAA. Weixlbaumer et al. (p. 953; see the Perspective by Liljas) present the crystal structure of release factor RF2 in complex with the UGA stop codon in the 70S ribosome. This work complements a recently published structure of RF1 bound to the UAA stop codon. Together these structures give us an insight into the specificity of release factor recognition of stop codons, as well as the mechanism of protein release.

  16. Pathways to Disease

    The recent progress in human genetics is the result of a decade-long scientific program. Efforts to identify disease-susceptibility genes, even if they have relatively small effects on risk, systematically reveal the biological pathways underlying a disease, which is a critical foundation for long-term progress in medicine. Altshuler et al. (p. 881) review the history of genetic mapping efforts, recent successes in whole-genome association studies, and challenges for the future.