Heating the Solar Atmosphere
One of the enduring mysteries in solar physics is why the Sun's outer atmosphere, or corona, is considerably hotter than its surface. In a Report in the 7 Jan 2011 Science, De Pontieu et al. presented observations from NASA's Solar Dynamics Observatory and Japan's Hinode satellite which suggest that the Sun's corona may be heated to millions of degrees by fountainlike jets of plasma, or spicules, that are propelled upward from the region immediately above the Sun's surface at 180,000 to 360,000 kilometers per hour (see the related ScienceNOW story by R.A. Kerr). The observations reveal that within its less-than-2-minute lifetime, a jet's temperature soars, with some parts reaching corona-like temperatures of 1 to 2 million degrees Kelvin (see the related video footage narrated by lead author Bart De Pontieu). Based on the ubiquity of the jets and the observed coronal intensities, the team estimates that the energy that jets deliver to the corona might well account for its heating. The results challenge current models for coronal heating and show that the interface region between the surface of the Sun and its corona plays a crucial role in energizing the solar atmosphere.
Early Southern Exodus?
The timing of the dispersal of modern humans out of Africa is a fundamental question in human evolutionary studies. Genetic and archeological data support an exodus along the Mediterranean by 60,000 years ago, but earlier attempts may have occurred. In a Report in the 28 Jan 2011 Science, Armitage et al. described artifacts found in Jebel Faya, United Arab Emirates, from about 100,000 years ago -- including stone hand axes, blades, and scrapers -- indicating that modern humans were already there by then. This location in eastern Arabia would have allowed access to the Fertile Crescent and India as sea level dropped. The results are particularly intriguing because the fierce deserts of the Arabian Peninsula have long been seen more as obstacles than conduits for human emigration out of Africa. The combination of artifacts found is remarkably similar to assemblages made during this period in East Africa, when Homo sapiens was the only known hominin on the continent. Still, an accompanying News story by A. Lawler noted that fossil bones from the site are needed before researchers can be absolutely certain that the tools found there were made by our own species and not more distant relatives such as Neandertals or even H. erectus.
Thwarting Bird Flu
Avian influenza is a persistent problem, directly challenging commercial chicken producers, threatening wild bird populations, and providing a reservoir for variants that might emerge as human pathogens. In a Report in the 14 Jan 2011 Science, Lyall et al. reported the first steps toward producing transgenic domestic chickens that block onward transmission of influenza virus. In this proof-of-principle experiment, the researchers generated transgenic chickens that express a short hairpin-shaped piece of RNA that acts as a decoy to the virus's polymerase, an enzyme required for viral replication. Instead of binding to the virus's genome, the polymerase instead attaches itself to the hairpin RNA, rendering the enzyme useless ( see the accompanying News story by M. Enserink). The researchers found that the transgenic chickens still succumbed to the virus when directly infected, but that they were not able to infect other birds. Although the ultimate goal is to make chickens completely resistant to the virus, this strategy offers the potential for significant advantages over vaccination, avoiding the challenges by strain variation and resistance. In a related podcast interview, senior author Laurence Tiley discussed the potential for using genetic modification to produce disease resistance in other important livestock.
Ammonites, Reconstructed
Ammonites, a group of cephalopods with external shells that went extinct roughly 65 million years ago, were among the most abundant marine invertebrates in Earth's history. Their paleobiology and position in the food web, however, are not well understood, due to the lack of preserved soft tissues. In a Report in the 7 Jan 2011 Science, Kruta et al. used a technique called synchrotron X-ray microtomography to reconstruct the mouthparts of three exceptionally well-preserved fossil specimens of the ammonite genus Baculites (see the accompanying video narrated by lead author Isabelle Kruta). Given the structural features of the lower and upper jaws and the shape of the radular teeth, the researchers surmise that these ammonites did not have the ability to capture large prey and cut it into small pieces. Rather, the jaw morphology, along with possible food remains found in the buccal mass of the digestive system of one specimen, suggests that ammonites likely fed on plankton. As noted in an accompanying Perspective by K. Tanabe, these findings may help explain why ammonites went extinct at the end of the Cretaceous, as there was an abrupt decline in several groups of plankton around the same time period.
Dinosaur Insights
Two Reports in Science this month described fossil finds that provide new insights in the evolution and reproductive biology of dinosaurs.
-- Martinez et al. (14 Jan 2011) reported the discovery of a very early dinosaur -- possibly a distant ancestor of Tyrannosaurus rex -- that lived about 230 million years ago, during what paleontologists call the dawn of the dinosaurs. The researchers say that the new finds -- two specimens that together make up a nearly complete skeleton of a diminutive, 1-meter-long dinosaur -- and neighboring fossils show that dinosaurs didn't outcompete other reptiles, but rather gradually replaced them as their predecessors died out for other reasons (see the related News story by M. Balter).
-- Lü et al. (21 Jan 2011) described a female fossil pterosaur from China that dates to 160 million years ago and includes an egg next to its pelvis. The egg is relatively small compared to the pterosaur body size and not hard like those of bird eggs, indicating a reproductive strategy more like that of some reptiles. A ScienceNOW story by S. Reardon highlighted the find.
Digesting Grass
The paucity of enzymes that efficiently deconstruct plant polysaccharides represents a major bottleneck for industrial-scale conversion of cellulosic biomass into biofuels. Cow rumen microbes specialize in degradation of cellulosic plant material, but most members of this complex community resist laboratory cultivation. In a study in the 28 Jan 2011 Science, Hess et al. have instead used metagenomics and single-genome sequencing to identify biomass-degrading genes and genomes. The team sequenced and analyzed a quarter terabase of DNA from microbes adherent to switchgrass incubated in cow rumen and identified nearly 28,000 genes related to known biomass-degrading families. Ninety candidate carbohydrate-degrading enzymes were synthesized and their activity analyzed against ten different substrates, including the biofuel crops miscanthus (a type of perennial grass) and switchgrass. The researchers also assembled draft genomes of 15 microbes that break down biomass material in nature, but resist cultivation in the lab. Together, these data sets greatly expand the catalog of genes and genomes that participate in the breakdown of cellulosic biomass and could be useful for the production of biofuel.
Expert Intuition
Experts in various cognitive fields show superior abilities not only for the quick perception of relevant input patterns but also for the rapid generation of appropriate responses. Board games provide a good opportunity to study the mechanisms underlying cognitive expertise because these games are played in accordance with a set of well-defined rules. In a Report in the 21 Jan 2010 Science, Wan et al. used functional magnetic resonance imaging to study brain activity of subjects playing shogi (Japanese chess). The team found that the precuneus, a part of the parietal cortex, was specifically activated by actual shogi patterns, but not by other objects, indicating that this brain region is important for the quick perception of patterns. Moreover, expert players -- but not amateurs -- showed activation in the caudate nucleus of the basal ganglia during quick generation of their "best next move." Neuropsychological, imaging, and animal studies suggest that the caudate nucleus is involved in goal-directed behavior, which in the case of a shogi game would be winning. Interestingly, when the expert players took their time and consciously evaluated a given board pattern, brain activation was limited to the prefrontal cortex and other cortical areas in both professional and amateur players. A related podcast feature considered how it is that expert players are able to process complicated information so quickly.
Core Reanalysis
Despite recent insight regarding the history and current state of the Moon from satellite sensing and analyses of limited Apollo-era seismic data, deficiencies remain in our understanding of the deep lunar interior. In a Report in the 21 Jan 2011 Science (published online 6 Jan), Weber et al. report on a reanalysis of Apollo lunar seismograms using modern analytical techniques. The team analyzed four types of seismic waves -- which differ in the direction of vibration -- from deep moonquakes clustered in 38 spots. They combined seismic records from each cluster to bring out any reflected signals and filtered the combined records to remove some of the noise. Their results indicate that the lunar core has a radius of 330 kilometers, and, like Earth's, consists of a solid inner core and molten outer core. Unlike Earth, however, the Moon also has a thick partial melt layer 150 kilometers thick resting above the outer core. A ScienceNOW story by R.A. Kerr, published on 6 Jan, highlighted the findings.
Seasonal Butterfly Switch
Current explanations for why sexual ornaments are found in both males and females include genetic correlation, same-sex competition, and mutual mate choice. In a Report in the 7 Jan 2011 Science, Prudic et al. revealed another mechanism by which sexual ornaments are maintained in both sexes: seasonal differences that correlate with a change in mating benefits to females and costs to males. The team showed that in the African butterfly Bicyclus anynana, males and females reciprocally change their sexual roles depending on their larval rearing temperatures. For larvae reared in the warmer wet season, adult males attract female attention by rapidly beating their wings to flash their distinctive ultraviolet-reflecting "eyespots". For larvae reared in the cooler dry season, adult females have more ornamented eyespots and actively court males (see the video narrated by senior author Antónia Monteiro). This developmental switch may benefit females in the dry season when food resources are scarce. Multiple matings especially with dry season males increase female lifespan and reproductive output as they may acquire high-quality bundles of sperm and associated nutrients from mating. Dry-season males, on the other hand, have a reduced lifespan when mated, while wet-season males do not. Leader author Kathleen Prudic discussed the work in a related podcast interview.
Electron Vortex Beams
The transmission electron microscope (TEM) has primarily been used by physical and life scientists for imaging structures and compositions ranging in size from atoms to cells. New applications are likely to emerge from recent demonstrations that it is possible to change the nature of the primary electron source used to created images. Now, in a Report in the 14 Jan 2011 Science, McMorran et al. report that passing an electron beam typically emitted in a TEM through carefully prepared holograms causes it to undergo diffraction and split into an electron vortex beam with a spiraling wavefront that carries orbital angular momentum. This type of beam can be used to create higher-resolution images of magnetic and biological specimens and to manipulate the structure and properties of samples, for example, by inducing currents in semiconductors, or making or breaking electronic bonds. An accompanying Perspective by R.A. Herring noted that "[n]ew types of electron beam lithography may enable the building of three-dimensional nanostructures in which atoms are picked up, moved, and set in place rapidly and accurately."
In Science Signaling
Survival Signal from Afar
A balance between cell survival and apoptosis is essential for animal development. Although proper development involves multiple interactions between the three embryonic germ layers -- the ectoderm, mesoderm, and endoderm -- little is known about the signaling pathways that promote cell survival in neighboring or distant germ layers. In the 18 Jan 2011 issue of Science Signaling, Endo et al. reported on an intertissue signaling pathway by which the endodermal and mesodermal layers promote the survival of the ectodermal layer. The evolutionarily conserved kinase SGK1 acts as a key signaling molecule in this pathway, which protects ectodermal cells from apoptosis by suppressing transcription of genes encoding components of a cell death–inducing signaling complex in the ectoderm. The initiating signal that triggers this pathway remains to be identified.
Also in Science Signaling this month:
-- Kondo and Perrimon identified unexpected players in the DNA damage response (4 Jan 2011)
-- Hall highlighted findings from Li and Matsunami, who reported a mechanism by which signaling crosstalk may enhance the sense of smell (11 Jan 2011)
-- Jacob et al. found that loss of the tumor suppressor Lkb1 has opposite effects on Hh and Wnt signaling (25 Jan 2011)
In Science Translational Medicine
Genetic Testing Enters the Genomic Era
There are more than a thousand severe childhood diseases that are inherited recessively. Preconception genetic testing for these diseases is important because a child may inherit the disease if both parents carry a mutant allele even if the parents don't appear to have the disease themselves. Currently, hospitals only screen prospective parents for a few of these disorders, such as Tay Sachs disease and cystic fibrosis. But the latest genome sequencing technologies are set to change preconception carrier screening by greatly expanding the number of diseases that can be tested for. This development is illustrated by a study by Bell et al. published in 12 Jan 2011 issue of Science Translational Medicine. These investigators combined target gene capture, next-generation genome sequencing, and sophisticated bioinformatics analysis to screen several hundred DNA samples simultaneously for 448 severe recessive diseases of childhood. Their study shows that it is feasible to use genome sequencing to screen for many recessive childhood disease mutations as long as the disease genes are known. But rolling out preconception carrier screening for a long list of diseases and to a much broader population raises many societal issues that are discussed by L. Jackson and R.E. Pyeritz in a Perspective and also by Jackson in a podcast interview.
Also in Science Transational Medicine this month:
-- Jacquemont et al. showed that an antagonist of a glutamate receptor improves symptoms in Fragile X syndrome patients who have a fully methylated promoter for FMR1, the gene mutated in this disease (5 Jan 2011)
-- Wang et al. showed that an adenylyl cyclase 1 inhibitor that acts on the anterior cingulate cortex in the brain alleviates neuropathic and inflammatory pain (also see the Perspective by R. Sharif-Naeini and Allan I. Basbaum) (12 Jan 2011)
-- Neff et al. found that a chimeric RNA therapeutic, comprising an RNA aptamer targeting the HIV-1 Env protein and a small interfering RNA that inactivates the tat/rev genes, blocks HIV infection in humanized mice (19 Jan 2011)
-- Ito et al. reported that blocking uroporphyrinogen decarboxylase (an enzyme involved in heme synthesis) using a small inhibitory RNA molecule, sensitizes head and neck cancer to radiation and chemotherapy (26 Jan 2011)
Image credits (in order of appearance):Bart De Pontieu; Photo by Norrie Russell, courtesy of Valerie White and The Roslin Institute; Photo by Mike Hettwer; Oliver Orschiedt/Wikimedia; William Peil and Antónia Monteiro
