The heavy fermion compound URu2Si2 enters an ordered phase below 17.5 kelvin but, despite 25 years of extensive study, the exact nature of this phase remains a mystery. Using very pure, small specimens, Okazaki et al. (p. 439) found that the magnetic susceptibility in the ordered phase breaks the fourfold rotational symmetry of the URu2Si2 crystal, which suggests that the hidden order is an electronic nematic state.
Laser BackfireStandoff detection is an important method to monitor or probe regions that are otherwise inaccessible to direct sampling techniques. Dogariu et al. (p. 442) report the observation of high-gain infrared lasing in air from the focal region of an ultraviolet laser. The backward-directed infrared laser light could then be used as a remote spectroscopic tool that samples the air on its return path back to the sender position. The technique should find a range of applications—from the detection of greenhouse gas emissions and pollution to the detection of potentially hazardous and explosive materials.
Reaction of Hydrogen Isotopes, Great and SmallKinetic isotope effects reveal mechanistic insight into chemical reactions. Larger isotope ratios often lead to larger changes in rate, and, commonly, the largest ratio is 2—for the substitution of deuterium for hydrogen. Fleming et al. (p. 448; see the Perspective by Alexander) compared results for the simplest chemical reaction, of an H atom with H2, for two hydrogen isotopes created with positive and negative muons, which provide an unprecedentedly large mass ratio of 36. At 500 kelvin, the relative reaction rates measured agreed with those calculated using variational transition state theory.
Warmest in 2000 YearsAlthough the climate warming of the past century has occurred nearly everywhere, the Arctic shows the greatest temperature increase. Most of the heat transported to the Arctic comes from the Atlantic Ocean, which has warmed greatly over the past 150 years. How did the temperature of Arctic inflow from the Atlantic vary before anthropogenic climate warming began? Spielhagen et al. (p. 450) present a record of oceanic temperature variations for the last 2000 years, which shows that Atlantic water entering the Arctic through the Fram Strait is warmer than it has been in two millennia. This unprecedented warming is likely to represent a key factor in the apparent transition toward an ice-free Arctic Ocean.
Before the Mediterranean ExodusModern humans originated in Africa and then spread to Eurasia and beyond. The timing and locations of their emigration have been uncertain; genetic and archaeological data support an exodus along the Mediterranean by 60,000 years ago, but earlier attempts may have occurred, for example, in response to the massive Toba volcanic eruption about 75,000 years ago. Armitage et al. (p. 453; see the news story by Lawler) now describe artifacts from about 100,000 years ago found in eastern Arabia, indicating that modern humans were already there by then. This location would have allowed access to the Fertile Crescent and India as sea level dropped. The findings suggest that there may indeed have been an early exodus of modern humans from Africa.
Predatory Synergism
Synergies between species, in which the combined effect of multiple species is greater than the sum of their individual effects, link biodiversity to ecosystem function, but these synergies may be sensitive to external influences. Piovia-Scott et al. (p. 461) investigated how a synergy between two very different predator species in the Bahamas was affected by the influx of resources from the adjacent ocean. Adding seaweed to entire small islands (simulating the natural marine-to-terrestrial energy transfer that occurs during storms) eliminated the synergistic effect of two predators—lizards and ants—on arthropod herbivores and their food plants, increasing the overall rate of herbivory.
Parasite Replication TriggerApicomplexan parasites, including Toxoplasma gondii and the malaria parasite Plasmodium falciparum, actively invade host cells. Little is known about the signals that govern initiation of replication once the parasite is intracellular. Apical membrane antigen 1 (AMA1) is released onto the parasite surface during invasion and cleaved by intramembrane proteolysis, mediated by a rhomboid-like serine protease, ROM4. Santos et al. (p. 473, published online 23 December; see the Perspective by Cowman and Tonkin) used conditional expression of Toxoplasma ROM4 to show that ROM4 activity is not essential for invasion, but instead is required for subsequent replication of the intracellular parasite. Furthermore, transgenic expression of the cleaved cytoplasmic tail of AMA1 alone—either from the Toxoplasma AMA1 or from its P. falciparum ortholog—completely restored the replicative capacity of the intracellular parasites. Thus, intramembrane cleavage of AMA1 is required to trigger parasite replication within the host cell.
Bigger Beats SmallerSocial cooperation has been the subject of intense experimental investigation, both in humans and in other animals, and recent studies have detailed the developmental origins of these representations in human children and infants. Thomsen et al. (p. 477) now document the appearance of social dominance awareness in infants before the end of the first year. Infants were found to be capable of representing the conflicting goals of two cartoon characters, appearing to use size as a cue to predict which character will win.
So Hungry I Could Eat MyselfAutophagy is a process by which eukaryotic cells engulf and breakdown cellular components to provide new substrates for metabolism. Egan et al. (p. 456, published online 23 December; see the Perspective by Hardie) report a biochemical mechanism by which low energy stores in a cell can be linked to autophagy. The authors searched for targets of the adenosine monophosphate–activated protein kinase (AMPK), which is activated when cellular concentrations of adenosine triphosphate are depleted. AMPK was found to regulate another protein kinase, ULK1, which functions in regulation of autophagy. Cells engineered so that ULK1 could not be phosphorylated by AMPK failed to respond properly to starvation, had decreased autophagy, and were prone to starvation-induced cell death.
MALT Lymphomagenesis RevisitedMucosa-associated lymphoid tissue (MALT) lymphoma, a type of B cell lymphoma, is associated with chronic inflammation. Many patients are successfully treated with antibiotics; however, patients whose lymphomas express the API2-MALT1 fusion oncoprotein as a result of a chromosomal translocation are resistant to this therapy. API2-MALT1–driven lymphomagenesis is associated with deregulated canonical nuclear factor B (NF-B) signaling; however, Rosebeck et al. (p. 468) now demonstrate that noncanonical NF-B signaling may also play a role. API2-MALT1, but not wildtype MALT1, cleaved the noncanonical NF-B signaling intermediate, NF-B–inducing kinase (NIK) driving constitutive noncanonical NF-B signaling. API2-MALT1–expressing cells exhibited great resistance to apoptosis and enhanced integrin-mediated adhesion, both of which were NIK-dependent. Tumor samples from patients with API2-MALT1–expressing tumors expressed higher levels of noncanonical NF-B genes compared with API2-MALT1–negative tumors. Thus, both canonical and noncanonical NF-B signaling are likely to contribute to MALT lymphomagenesis.
Unsubscribe or edit your subscriptions for this service at: http://www.sciencemag.org/cgi/alerts/main Written requests to unsubscribe may be sent to:
| ||||||||||||||||||||
Evolution
This e-mail was sent to bloggernyaagus.jawabansurat@blogger.com
To get on and off our e-mail lists, please change your e-mail preferences here.
If you need additional help, please write to memuser@aaas.org .
AAAS / Science
1200 New York Avenue NW
Washington, DC 20005
U.S.A.
Telephone: +1 202-326-6417
Toll Free in the U.S.: 866-434-(AAAS) 2227
E-mail: membership@aaas.org
Privacy Policy:
http://www.sciencemag.org/help/readers/privacy.dtl
[ AAAS / Science does not endorse any 3rd party products or services advertised here. ]
© 2010 American Association for the Advancement of Science. All Rights Reserved.
Tidak ada komentar:
Posting Komentar