 This month in Science Roundup:
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When you give someone the gift of a AAAS membership, they get a subscription to Science, and so much more. Your gift goes to support real world programs that are making an impact in areas including: science policy, diplomacy, public engagement and dialogue, workforce development and diversity, and education. REPORT: Pattern in Escalations in Insurgent and Terrorist Activity Abstract: In military planning, it is important to be able to estimate not only the number of fatalities but how often attacks that result in fatalities will take place. We uncovered a simple dynamical pattern that may be used to estimate the escalation rate and timing of fatal attacks. The time difference between fatal attacks by insurgent groups within individual provinces in both Afghanistan and Iraq, and by terrorist groups operating worldwide, gives a potent indicator of the later pace of lethal activity. Supporting online material BREVIA: A Biological Screw in a Beetle's Leg Abstract: The coxa-trochanteral joints on the legs of the weevil Trigonopterus oblongus (Pascoe) work as a biological screw-and-nut system. The apical portions of the coxae closely resemble nuts with well-defined inner threads covering 345°. The corresponding trochanters have perfectly compatible external spiral threads of 410°. Supporting online material RESEARCH ARTICLE: Widespread RNA and DNA Sequence Differences in the Human Transcriptome Abstract: The transmission of information from DNA to RNA is a critical process. We compared RNA sequences from human B cells of 27 individuals to the corresponding DNA sequences from the same individuals and uncovered more than 10,000 exonic sites where the RNA sequences do not match that of the DNA. All 12 possible categories of discordances were observed. These differences were nonrandom as many sites were found in multiple individuals and in different cell types, including primary skin cells and brain tissues. Using mass spectrometry, we detected peptides that are translated from the discordant RNA sequences and thus do not correspond exactly to the DNA sequences. These widespread RNA-DNA differences in the human transcriptome provide a yet unexplored aspect of genome variation. Supporting online material  INTRODUCTION TO SPECIAL ISSUE: A Universe of GalaxiesFull Text: It wasn't until the 1920s that astronomers realized that there were other galaxies in the universe besides our own. Using the 100-inch telescope at Mount Wilson in California, Edwin Hubble determined the distance to Andromeda (M31) and to the Triangulum (M33) and concluded that each was an "isolated system of stars and nebulae, lying far outside the limits of the galactic system." Before that, these and other galaxies were classified as nebulae, extended objects other than planets or comets; although their location was a matter of great debate, they were generally thought to be within our galaxy. PERSPECTIVE: Sex, Death, and the Red Queen Summary: Sex is hard to explain. Since males can't reproduce by themselves and often contribute nothing except genes to offspring, a population of asexual females can grow at double the rate of a population that reproduces sexually. Why then, given this “cost of males,” do most plants and animals indulge in biparental sex? One possible solution is that sex accelerates adaptation; the Red Queen hypothesis, for example, proposes that sex gives plants and animals an edge in the never-ending battle against their coevolving parasites. Although researchers have collected empirical field data consistent with the Red Queen hypothesis from a range of natural host-parasite systems, direct experimental evidence that coevolving parasites select for sex in their hosts has proven elusive. On page 216 of the 8 July 2011 of issue Science, Morran et al. pin down some of that direct evidence. In laboratory experiments, they grew several populations of nematode worms, some with and some without a bacterial parasite, to provide the most definitive support yet for the Red Queen's answer to why sex evolved. Related Article REPORT: A Pericyte Origin of Spinal Cord Scar Tissue Abstract: There is limited regeneration of lost tissue after central nervous system injury, and the lesion is sealed with a scar. The role of the scar, which often is referred to as the glial scar because of its abundance of astrocytes, is complex and has been discussed for more than a century. Here we show that a specific pericyte subtype gives rise to scar-forming stromal cells, which outnumber astrocytes, in the injured spinal cord. Blocking the generation of progeny by this pericyte subtype results in failure to seal the injured tissue. The formation of connective tissue is common to many injuries and pathologies, and here we demonstrate a cellular origin of fibrosis. Related Podcast NEWS & ANALYSIS: Searching for the Google Effect on People's Memory Summary: In four cleverly designed experiments reported online in the 14 July 2011 of issue Science, psychologists explore how the Internet may be changing the way people handle information. The results, the researchers say, confirm a growing belief that people are using the Internet as a personal memory bank: the so-called Google effect. What surprised the researchers most was not people's reliance on online information but their ability to find it.  REVIEW: Trophic Downgrading of Planet Earth
Abstract: Until recently, large apex consumers were ubiquitous across the globe and had been for millions of years. The loss of these animals may be humankind's most pervasive influence on nature. Although such losses are widely viewed as an ethical and aesthetic problem, recent research reveals extensive cascading effects of their disappearance in marine, terrestrial, and freshwater ecosystems worldwide. This empirical work supports long-standing theory about the role of top-down forcing in ecosystems but also highlights the unanticipated impacts of trophic cascades on processes as diverse as the dynamics of disease, wildfire, carbon sequestration, invasive species, and biogeochemical cycles. These findings emphasize the urgent need for interdisciplinary research to forecast the effects of trophic downgrading on process, function, and resilience in global ecosystems. Supporting online material  REPORT: Precise Manipulation of Chromosomes in Vivo Enables Genome-Wide Codon Replacement
Abstract: We present genome engineering technologies that are capable of fundamentally reengineering genomes from the nucleotide to the megabase scale. We used multiplex automated genome engineering (MAGE) to site-specifically replace all 314 TAG stop codons with synonymous TAA codons in parallel across 32 Escherichia coli strains. This approach allowed us to measure individual recombination frequencies, confirm viability for each modification, and identify associated phenotypes. We developed hierarchical conjugative assembly genome engineering (CAGE) to merge these sets of codon modifications into genomes with 80 precise changes, which demonstrate that these synonymous codon substitutions can be combined into higher-order strains without synthetic lethal effects. Our methods treat the chromosome as both an editable and an evolvable template, permitting the exploration of vast genetic landscapes. Supporting online material  NEWS FOCUS: Why Do Parrots Talk? Venezuelan Site Offers Clues Summary: The world's longest-running study of wild parrots is entering its 24th year, making it the parrot equivalent of Jane Goodall's long-term study of chimpanzees in Tanzania and Cynthia Moss's elephant project in Kenya. And just as those studies tracking individual animals changed our understanding of chimpanzees and elephants, this one is opening new windows into the minds and behaviors of parrots. Researchers have discovered details of the parrotlets' ecology and life histories, and the project has now entered a new phase focusing on their communicative skills. Last week, researchers reported that the contact calls of wild parrotlet nestlings—vocalizations that function much like a name—are not genetically programmed. Instead, they learn these calls from their parents, almost like human children learning their names. It is the first study to provide experimental evidence for learned vocalizations in wild parrots. Podcast Interview REPORT: Cilia-Like Beating of Active Microtubule Bundles Abstract: The mechanism that drives the regular beating of individual cilia and flagella, as well as dense ciliary fields, remains unclear. We describe a minimal model system, composed of microtubules and molecular motors, which self-assemble into active bundles exhibiting beating patterns reminiscent of those found in eukaryotic cilia and flagella. These observations suggest that hundreds of molecular motors, acting within an elastic microtubule bundle, spontaneously synchronize their activity to generate large-scale oscillations. Furthermore, we also demonstrate that densely packed, actively bending bundles spontaneously synchronize their beating patterns to produce collective behavior similar to metachronal waves observed in ciliary fields. The simple in vitro system described here could provide insights into beating of isolated eukaryotic cilia and flagella, as well as their synchronization in dense ciliary fields. Supporting online material REPORT: Experimental and Theoretical Differential Cross Sections for a Four-Atom Reaction: HD + OH → H2O + D Abstract: Quantum dynamical theories have progressed to the stage in which state-to-state differential cross sections can now be routinely computed with high accuracy for three-atom systems since the first such calculation was carried out more than 30 years ago for the H + H2 system. For reactions beyond three atoms, however, highly accurate quantum dynamical calculations of differential cross sections have not been feasible. We have recently developed a quantum wave packet method to compute full-dimensional differential cross sections for four-atom reactions. Here, we report benchmark calculations carried out for the prototypical HD + OH → H2O + D reaction on an accurate potential energy surface that yield differential cross sections in excellent agreement with those from a high-resolution, crossed–molecular beam experiment. Supporting online material In Science Signaling RESEARCH RESOURCE: Real-Time Imaging of Notch Activation with a Luciferase Complementation-Based Reporter
RESEARCH ARTICLE: PreTCR and TCR γδ Signal Initiation in Thymocyte Progenitors Does Not Require Domains Implicated in Receptor Oligomerization
EDITORS' CHOICE: Use It, Then Lose It
In Science Translational Medicine RESEARCH ARTICLE: Rational Design of a Meningococcal Antigen Inducing Broad Protective Immunity
RESEARCH ARTICLE: A Common Mutation in the Defensin DEFB126 Causes Impaired Sperm Function and Subfertility
IMAGE CREDITS (In order of appearance): NASA/JPL-CALTECH, NICHOLAS SLY
Sponsored by:
AAAS + U = Δ
When you give someone the gift of a AAAS membership, they get a subscription to Science, and so much more. Your gift goes to support real world programs that are making an impact in areas including: science policy, diplomacy, public engagement and dialogue, workforce development and diversity, and education. |