Editors' Choice

Science  21 Oct 2005:
Vol. 310, Issue 5747, pp. 407

    Surveying Influenza

    1. Caroline Ash

    Wild influenza viruses circulate in waterfowl, and mallard ducks (Anas platyrhynchos) are particularly good reservoirs, capable of transmitting most of the 16 known hemagglutinin (HA) subtypes of influenza A. Viruses of HA subtype H5 and H7, commonly found in mallards, can transform into highly pathogenic forms when introduced into domesticated poultry via the addition of basic amino acid residues in the HA cleavage site, including that of H5N1, responsible for more than 100 human deaths in Southeast Asia and the current source of fears of a human pandemic. Over 4 years, Munster et al. have been surveying and sequencing influenza A subtypes circulating in migrant mallards in northern Europe. Unsurprisingly, but nonetheless alarming, they have discovered that highly related H5 and H7 were circulating in wild ducks before epidemics of highly pathogenic influenza in poultry in Italy (1997 and 2000) and the Netherlands (2003). This sort of surveillance could be a valuable early warning system, allowing time to make vaccines up-to-date. The World Health Organization has also been surveying H5N1 avian influenza viruses with a view to monitoring adamantane drug resistance and antigenic drift, and hence to developing a predictive strategy for vaccine preparation. — CA

    Emerg. Infect. Dis. 11, 1545; 1515 (2005).


    Sleep Consolidates Visual Experience

    1. Peter R. Stern

    Sleep is important for learning and for memory formation. However, there is much controversy about the impact of sleep on brain plasticity and the mechanisms underlying these observations. Jha et al. tested whether local brain activity during sleep was necessary for the establishment of brain plasticity. They used the well-established phenomenon of ocular dominance plasticity, in which monocular deprivation shifts synaptic activity in the primary visual cortex (area V1) of the cat in favor of the nondeprived eye only during a critical developmental period. By pharmacological blockade of action potentials they managed to reversibly silence area V1 only during sleep. Although control animals showed the normal critical period ocular dominance shift, this phenomenon could be prevented by selectively silencing area V1 during sleep. Additional undisturbed sleep after a period of cortical inactivation did not rescue this cortical plasticity. Thus, specific neuronal activity in the affected brain area during sleep immediately after waking experience is required for the consolidation of ocular dominance plasticity. — PRS

    J. Neurosci. 25, 9266 (2005).


    Spongy Clay?

    1. Marc S. Lavine

    Exfoliated clays have been used to reinforce and compatibilize polymeric materials. Clays have also been added to temperature-responsive hydrogels to improve their properties by strengthening the hydrogels without severely degrading their thermoresponsive behavior. Recently, a technique was found to make clay aerogels, which are highly porous structures with very low densities. Bandi et al. infiltrated a hydrophilic clay aerogel with N-isopropylacryl-amide monomer, which was polymerized in situ in order to produce a polymer-clay composite that preserves the aerogel structure of the clay. The resulting composite retains a low density and good stability, with phase transition and swelling behavior similar to that of the unmodified polymer. The clay aerogel improved the structural integrity of the polymer. At the same time, the polymer prevented loss of the aerogel structure when the composite was immersed in water, even though the unmodified hydrogel has little structural integrity of its own. The composites could be cycled through several dehydration-hydration cycles without any breakdown in the structure or performance of the aerogel hydrogel. — MSL

    Macromolecules 10.1021/ma051698+ (2005).


    Stem Cells by a Whisker

    1. Lisa D. Chong

    During normal mammalian hair growth, hair follicles undergo phases of growth, regression, and rest throughout the life of the animal. At the onset of the growth phase, cells recruited from the hair bulge form a hair germ, from which a new hair bulb develops. The adult hair bulge harbors keratinocyte cells, some of which are capable of clonal growth in cell culture, which may represent progenitor cells that underlie the formation of different hair follicle cell lineages or may be multipotent stem cells that can sustain long-term hair follicle renewal.

    Claudinot et al. now show that these follicular cells are bona fide mammalian stem cells. Single keratinocytes were isolated from the whisker follicles of adult rats, labeled and expanded in cell culture, and then injected into the skin of newborn mice when pelage hair was just being formed. Grafts were subsequently transplanted into nude mice. In some mouse hair follicles, all eight cell lineages present were constituted of entirely transplanted cells, including the root sheaths, hair shaft, sebaceous glands, and epidermis. Transplanted cells were still found after several hair cycles, which suggests that clonogenic keratinocytes are true multipotent stem cells. Furthermore, the transplanted rat cells retained the capacity to recognize and home to the mouse follicle hair bulge. In the future, stem cells from human hair follicles could be exploited to regenerate hair and reconstruct tissue in patients. — LDC

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.0507250102 (2005).


    Sea Ice Amplification

    1. H. Jesse Smith

    Numerous, millennial-scale warming episodes, called Dansgaard-Oeschger (D-O) events, punctuated the last glacial period. These events, first discovered in deep ice cores from Greenland, are visible in climate records extending from pole to pole, and in Pacific as well as Atlantic marine sediments. One popular hypothesis about the cause of these abrupt climate warmings invokes changes in the strength of the ocean's thermohaline circulation, which affect ocean heat transport. Such a model, however, cannot explain the size of the temperature swings in Greenland, which were as large as 5° to10°C. Li et al. use an atmospheric general circulation model to show that warming and cooling of the magnitude observed in Greenland can be caused by only small changes in the amount of sea ice around it. Furthermore, the sea ice changes that they suggest would also account for variations in snow accumulation and oxygen isotope composition similar to those measured in ice cores from Greenland. Finally, the amount of sea ice retreat proposed is consistent with forcing either by ocean thermohaline circulation variations, or by changes in surface wind stress in the North Atlantic. Thus, sea ice can provide a positive feedback strong enough to cause warming like that which occurred during D-O events. — HJS

    Geophys. Res. Lett. 32, L19702 (2005).


    One After Another

    1. Jake S. Yeston

    Multistep synthesis is more efficient when two or more reactions are run consecutively in the same flask, thereby eliminating isolation and purification steps. Huang et al. show that a single catalyst can sequentially facilitate nucleophilic and electrophilic additions to α,β-unsaturated aldehydes (compounds with adjacent C=C and C=O groups), with both steps proceeding in high enantioselectivity. Initial reaction of the chiral imidazolidinone catalyst at the C=O group yields an iminium intermediate that adds furan, indole, and thiophene-derived nucleophiles at the β-carbon of the C=C group. The product then remains activated toward addition of electrophilic chlorine at the α-carbon. Moreover, the catalyst- reagent interactions dominate the reaction kinetics, selecting for a syn addition geometry in which both nucleophile and electrophile bond to the same face of the olefin, despite the unfavorable sterics of this arrangement. Overall yields are in the 60 to 90% range, with 9 to 1 or greater syn selectivities, and 99% enantiomeric excess of the major product. Hydride nucleophiles can be added as well, and a fluorine electrophile substituted for the chloro compound. Selectivity switches with hydride to favor the anti product, although a syn geometry can still be induced by addition of an alternate catalyst after the nucleophilic step. — JSY

    J. Am. Chem. Soc. 10.1021/ja055545d (2005).


    Quick-Release RNA

    1. Paula A. Kiberstis

    After it is transcribed from DNA, eukaryotic messenger RNA (mRNA) undergoes various types of processing, including the addition of a polyadenylate [poly(A)] tail. The mRNA then typically moves out of the nucleus and into the cytoplasm, where it is translated into protein. However, a large fraction of poly(A)+ RNA stays within the nucleus.

    Prasanth et al. now suggest that this nuclear-retained RNA may be part of a gene-regulatory mechanism that ensures rapid translation of mRNAs that are required for cellular defenses against stress. They found two populations of poly(A)+ RNA derived from the mouse gene encoding cationic amino acid transporter 2, a protein critical for the activation of the nitric oxide signaling pathway (a common response to stress). In addition to the conventional protein-coding mCAT2 mRNA present in the cytoplasm, a second transcript (CTN-RNA) was retained in the nucleus by virtue of its distinct 3' untranslated region (UTR). When cells were exposed to stress, the latter RNA was rapidly cleaved at its 3'UTR and released into the cytoplasm. This nuclear RNA release mechanism may thus control the expression of a variety of proteins whose activity is required rapidly in response to stress or other cellular signals. — PAK

    Cell, in press.