2 DECEMBER 2011 VOL 334 SCIENCE www.sciencemag.org 1180

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I Know You >>The paper wasp, Polistes fuscatus, which lives in multiple queen social groups, is able to differentiate among individuals based on varying fa-cial markings. This suggests that this species has evolved the ability to learn and recognize facial features as a response to their highly social environment. However, this ability could also be due to a well-developed form of pattern recognition. To differentiate among these hypotheses, Sheehan and Tibbets (p. 1272) compared the facial learning ability in P. fuscatus to that in a related species, P. metricus, which nests singly. P. fuscatus wasps were able to learn faces much more accurately than they were non-face (or manipulated face) images. Furthermore, P. met-

ricus wasps were unable to learn faces, despite the fact that both species were able to differentiate equally among images of prey or patterns.

Exploiting X-raysX-rays have been used to study materials for a long time, from examining broken bones, to identifying the crystal structure of proteins. The development of high-intensity centralized facilities now allows the study of more scientifi c questions, including those involving dynamic behavior. Advances in optics have also made it possible to focus x-rays, making it possible to look at localized behavior. Ice et al. (p. 1234) review the developments in beam sources and focusing methods and highlight a wide range of studies now using x-ray techniques.

Diamond Quantum MechanicsThe separation between the classical and quantum me-chanical worlds is becoming less distinct. Experiments are beginning to reveal quantum mechanical behavior in a variety of macroscopic systems. Lee et al. (p. 1253; see the Perspective by Duan) generated and verifi ed entanglement between the vibrational modes of two macroscop-ic diamonds at room temperature. The results confi rm that quantum phenomena may persist in ambient conditions in a laboratory-scale system and point toward a possible platform for ultra-fast quantum information processing at room temperature, based on optical phonons.

Make HydrogenMature technologies exist to generate hydrogen from water, using electric power, but vigorous efforts are now under way to enhance the effi -

ciency of the process on account of its potential importance in renewable energy. Subbaraman

et al. (p. 1256) combined nickel oxide and plat-inum to produce a more effective catalyst than either component alone. The fi ndings suggest that the nickel helps to cleave the O-H bond, and the platinum then directs the separated H intermediates to form H2.

Missing Metals?Before the fi rst stars formed, the only elements present in the universe were hydrogen, helium, and lithium. All the other elements, which astron-omers refer to as metals, were produced in stars. Fumagalli et al. (p. 1245, published online 10 November; see the Perspective by Kacprzak)

report the detection of two gas clouds without discernible metals. These clouds date to about two billion

years after the Big Bang, an epoch by which plenty of stars and galaxies had formed

and thus by which most of the gas in the universe was expected to have been enriched with metals. Thus, the transport of metals from stars and galaxies to their surroundings was not as effi cient or as homogeneous as previously assumed.

Cooperating to Ice HistoriesAntarctica has been covered with ice for the past 34 million years. Falling concentrations of atmospheric CO2 have been the prime suspects in causing the cooling that produced the accumulation of ice, but reconstructions of atmospheric CO2 content have contradicted this notion. Pagani et al. (p. 1261) present

alkenone-based CO2 reconstructions, from both high- and low-latitude sites in the Atlantic and Southern oceans, which show that CO2 levels did in fact decline precipitously just prior to and during the onset of glaciations, confi rming that CO2 played a dominant role in the inception of Antarctic glaciation. The temperature histories of Antarctica and the Arctic during the last degla-ciation are quite different. What about changes in the masses of the ice sheets? Weber et al.

(p. 1265) present marine sedimentary records from the Weddell Sea coast of the East Antarctic ice sheet which show that the ice sheet reached its maximum extent contemporaneously with that of Northern Hemispheric ice sheets.

Yeast Model of Alzheimer’s DiseaseYeast cell biology has yielded fundamental insight into a variety of processes involved in human disease. Treusch et al. (p. 1241, published online 27 October; see the Perspec-tive by McGurk and Bonini) have now created a yeast model of the cellular toxicity caused by the beta-Amyloid peptide Aβ 1-42, which is thought to be causal in Alzheimer’s disease (AD). An unbiased genome-wide screen for modifi ers of toxicity revealed the yeast homolog of PICALM, a confi rmed AD risk factor involved in endocytosis. Three additional genes were also identifi ed that appear to impact AD risk, based on their as-sociations with AD onset and pathologic burden. A model of Aβ toxicity in the glutamatergic neurons of nematodes was created and used to confi rm the role of the toxicity modifi ers. PICALM was also shown to protect rat cortical neurons from toxic Aβ oligomers.

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This Week in Science

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Diffusing Healthy BehaviorHow can we infl uence people to adopt healthy behaviors? While support groups are helpful in this regard, studies have suggested that having similar people together (a condition known as homophily) may not help to spread information about health innovations. Centola (p. 1269; see the Perspec-tive by van der Leij) devised an online experiment which controlled the extent of homophily and the structure of an online community network. Participants were randomly assigned to a group in which the network structure was the same, but, in one case, the participants were connected to similar part-ners. While in the other group, the partners had random characteristics. In the homophilic group, the subjects were more likely to adopt the healthy behavior (for example, sign up for a health diary).

Cancer Cell Vulnerability Many cancer cells express an alternatively spliced form of the metabolic enzyme pyruvate kinase, pyruvate kinase M2 (PKM2). PKM2 is thought to help cancer cells use glucose effi ciently to help in the production of molecules required for rapid cellular proliferation. Anastasiou et al. (p. 1278, published online 3 November; see the Perspective by Hamanaka and Chandel) now report another advantage for cancer cells expressing PKM2. PKM2 is sensitive to oxidation by reactive oxygen species (ROS), which decreases its activity. Alterations in cancer cells and properties of their environment tend to increase ROS levels, causing toxicity. Inhibition of PKM2 appears to combat toxicity by promoting metabolic changes that help the cell to cope with the excess ROS. Thus, promoting sustained acti-vation of PKM could offer a way to selectively target cancer cells.

Parasite Paradise?The human malaria parasite, Plasmodium falciparum, has exerted an evolutionary pressure on the human population that has led to the selection of various polymorphisms in hemoglobin that protect carri-ers against severe malaria-related disease and death. Cyrklaff et al.

(p. 1283, published online November 10) now show that the malaria parasite “mines” actin from the erythrocyte’s membrane skeleton to generate an actin cytoskeleton associated with the Maurer’s cleft ma-chinery involved in the transfer of parasite proteins to the erythrocyte surface. In parasitized erythrocytes containing hemoglobin S or C, actin remodeling by the parasite is impaired, resulting in an aberrant actin cytoskeleton and degenerated Maurer’s clefts.

Meiosis MattersDuring meiosis, diploid cells make four haploid gametes or spores. In the fi rst meiotic division, homologous chromosomes become physically connected through carefully controlled DNA breaks that initiate crossing over. These connections, or chiasmata, facilitate the correct segregation of the homologs and drive the recombination that occurs during sexual reproduction. Rosu et al. (p. 1286) analyzed the regulation of crossing over in Caenorhabditis elegans and found that even a single DNA break in a homolog was converted with high effi ciency into a cross-over event. The ability of the homologs to interact through DNA breaks was temporally regulated, fi rst to ensure that crossing over did indeed occur, and then to ensure that the number of cross-overs was limited.

More than a ScratchImmunological T cells that express the γδ T cell receptor respond rapidly to various stressors in the skin by binding to stress-induced ligands. It is thought that this response helps to prevent dissemination of an infection or to restore tissue homeostasis after injury. The effects of this “lymphoid stress surveillance” response are primarily local; however, systemic effects on the im-mune response are possible. Working in mice, Strid et al. (p. 1293) show that antigen given in the context of mild skin abrasion can induce a systemic T helper 2 (TH2)–type immune response. TH2 responses are most commonly associated with allergy and asthma. In this case, the induction of the TH2 response was dependent on lymphoid stress surveillance: Skin-resident γδ T cells were required for the response, as was the receptor NKG2D, which γδ T cells use to recognize molecules that are induced in response to physicochemical stress. Thus, skin allergies may arise when nor-mally benign antigens are encountered at the same time as a tissue injury or abrasion.

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