This month in Science Roundup:
Recent reports have suggested that most of the world’s commercial fisheries could collapse within decades. Although poor fisheries governance is often implicated, evaluations of solutions remain limited. In a Report in the 19 Sep 2008 Science, Costello et al. assessed the effectiveness of rights-based fisheries management in preventing the collapse of fisheries. In such schemes, fishermen (or fishing cooperatives) are given the exclusive and guaranteed right to harvest a given quantity of fish in a particular fishery during the fishing season. The idea is that these allocated rights, or catch shares, give fishermen the incentive not to overharvest. By analyzing a global database of fisheries institutions and catch statistics in 11,135 fisheries from 1950 to 2003, the team found that rights-based fishing halves the chances of economic collapse. Although the global rate of catch-share adoption has increased since 1970, the fraction of fisheries managed with catch shares is still small. The new findings suggest that as catch shares are increasingly implemented globally, fish stocks, and the profits from harvesting them, have the potential to recover substantially. An accompanying News story by E. Stokstad highlighted the Report.
Damage Control for the Heart
Cardiac ischemia is a condition characterized by inadequate blood flow to the heart, which can result in the accumulation of toxic metabolites that cause irreversible tissue damage to the heart muscle. Not surprisingly, there is substantial interest in the development of drugs that can limit the extent of ischemia-induced cardiac damage resulting from heart disease or even cardiac surgery. In the 12 Sep 2008 Science, Chen et al. reported on a promising candidate. Studying rodent models, the team found that a mitochondrial enzyme called aldehyde dehydrogenase 2 (ALDH2) was consistently activated in hearts that were most resistant to ischemia-induced damage. A subsequent high-throughput screen of tens of thousands of compounds yielded a small molecule activator of ALDH2 (Alda-1) that, when administered to rats before an ischemic event, reduced the extent of heart damage by 60%. This protective effect is likely due to decreased formation of toxic aldehydes. The finding suggests that Alda-1 or related compounds might be used therapeutically to minimize heart damage in controlled settings such as during coronary bypass surgery. Senior author Daria Mochly-Rosen discussed the work in a related podcast interview.
Memory Recall in the Hippocampus
The hippocampus has been intensely studied for its role in recording memories. Now two studies reported in Science suggest that patterns of neuron firing in the hippocampus are also involved in recalling past experiences (see the News story by G. Miller). In a rat study described in the 5 Sep 2008 issue, Pastalkova et al. recorded hippocampal activity in rodents trained to alternate between the left and right arms of a figure-eight maze. During the delay period in between runs, which the rats spent on a running wheel, the team found that each moment in time was characterized by the firing of a particular assembly of neurons that formed a highly specific activity sequence across time. Interestingly, the researchers observed the same pattern of activity, over the same time course, when the mice were running through the mazes -- which suggests that these firing sequences represent the brain’s internal mechanism for planning (or reminding itself) what it has to do next (listen to a related podcast interview with senior author G. Buzaki). In a second study reported in Science Express on 4 Sep, involving epilepsy patients with surgically implanted brain electrodes, Gelbard-Sagiv et al. found that the firing patterns of neurons recorded in or near the hippocampus of people watching a video episode were the same as those recorded during later recall of the same show. Moreover, the neurons fired even before the people told the researchers that the memory of the show had "come to mind," suggesting a direct link between free recall and neuron "replay" in this portion of the brain.
Why do people overbid in auctions? Is it bidders’ desire to win or their aversion to losing that drives sale prices up? In a Report in the 26 Sep 2008 Science, Delgado et al. investigated this question by using functional magnetic resonance imaging (fMRI) to monitor the brain activity of participants in an auction. Their data revealed greater activity (as measured by changes in blood-oxygen level) in the striatum -- a brain region implicated in responses to monetary gains or losses -- in response to losing as opposed to winning. Moreover, greater overbidding correlated with the magnitude of the response to losing. This suggested to the researchers that a fear of losing a social competition may be what prompts overbidding. To further test this hypothesis, they designed a behavioral experiment in which the ground rules of the auction were modified so as to emphasize the potential for loss without altering the basic possibility of winning. Under these conditions, the tendency to overbid was magnified. These results run counter to the idea that the "joy of winning" mediates overbidding. The teams suggest that although their findings do not rule out a role for risk aversion in the tendency to overbid, they do suggest that the fear of losing or social loss aversion may be an important factor. A related Perspective by E. Maskin highlighted considered the broader question of whether neurobiology can guide economic experiments and refine economic models.
Death Shapes Development
Apoptosis, or programmed cell death, occurs throughout animal development and is critical for maintaining adult homeostasis, as well as for removing unnecessary cells to shape embryonic development. In a Report in the 19 Sep 2008 Science, Toyama et al. revealed that apoptosis also contributes to the mechanical forces that drive cell movements during embryogenesis. The team investigated the process of dorsal closure in the fruit fly -- a model system for wound healing and cell sheet morphogenesis during development -- during which two sheets of epithelial cells advance to cover an eye-shaped opening in the developing embryo. Through a detailed biomechanical analysis that combined high-resolution imaging and cell and genetic manipulation, the researchers found that apoptosis contributes between one-third and one-half of the force needed to seal the dorsal epithelium over the embryo. As cells die and the cellular remains are extruded inward to the embryo, neighboring cells are elongated toward the apoptotic cell in order to maintain a continuous dorsal surface. Suppressing apoptosis slowed dorsal closure, while enhancing apoptosis speeded up the process relative to wild-type embryos. The results raise the possibility of a dynamic role for apoptosis in other morphogenic processes including tissue reconstruction in wound healing. An accompanying Perspective by L. A. Davidson highlighted the study.
Science as Art
In a world in which images and videos are primary means of communication, new ways of conveying scientific data are essential -- not only for increasing public understanding of science and engineering, but also for improving communication across scientific disciplines. In a special section of the 26 Sep 2008, Science, in partnership with the National Science Foundation, presented the winners and honorable mentions in the sixth annual International Science & Engineering Visualization Challenge. This year’s contest drew 181 entries from 20 U.S. states and the District of Columbia and 20 countries. The winners -- in categories including photography, illustration, informational graphics, and multimedia -- captured the crystalline beauty of diatoms, the expanse of the human circulatory system, a fairy tale tea party re-invented, and the dynamic lives of plant cells. An online slide presentation showcased the honorees, and a related podcast interview with finalist judge Alisa Machalek discussed what makes a winning scientific image.
Fuels from Sugars
Dwindling petroleum reserves and growing concerns about global climate change have hastened research into alternative fuels derived from renewable resources. In a Report published online in Science Express on 18 Sep 2008, Kunkes et al. described a catalytic approach for converting sugars from plant biomass -- such as glucose and sorbitol -- to liquid transportation fuels. One of the key challenges for converting carbohydrates from plant matter into fuel has been removing most or all of the oxygen atoms in the reactants in order to form molecules that have the right properties for combustion. To address this problem, the team devised a two-stage system, in which an initial reactor equipped with a platinum-rhenium catalyst breaks down aqueous sugar into alcohol and carbonyl compounds (such as ketones and carboxylic acids), which can then be directed into a second reactor for assembly into hydrocarbon chains. Depending on the catalyst used in this latter step, the system can be used to produce branched hydrocarbons and aromatic compounds for gasoline, or longer chain, more linear hydrocarbon chains used in diesel and jet fuels. The researchers note that the approach is sufficiently simple that it can be relatively inexpensive, and is sufficiently flexible that it can be employed to produce a variety of liquid fuel components. Moreover, the intermediate compounds from the first reactor can also serve as valuable compounds for the fine chemical and polymer industries.
Melting Glaciers, Rising Seas
Warming glaciers can raise sea level in two main ways: by adding more water as they melt, and by discharging ice into the ocean through fast-moving ice streams and outlet glaciers. The incidence of this latter phenomenon has soared in recent years, but researchers haven’t been able to understand the process sufficiently to gauge its contribution to sea-level rise. As a result, the most recent assessment by the Intergovernmental Panel on Climate Change, which projects up to 60 centimeters of sea level rise by 2100, chose not to factor ice loss through glacier flow into its estimate. Now, in a Report in the 5 Sep 2008 Science, Pfeffer et al. have tackled the issue of glacier dynamics by calculating how much ice discharge from outlet glaciers in Greenland and Antarctica would be required to produce various rates of sea level rise, and then evaluating the plausibility of those discharge rates. As noted in a related ScienceNOW story by R. A. Kerr, the team concludes that sea level rise in excess of 2 meters, as has been estimated by some researchers, is unlikely -- and that a more reasonable approximation is an increase between 80 centimeters and 2 meters by the end of the century. In a related podcast interview, lead author Tad Pfeffer discussed the need to better understand glacier physics in order to improve upon current models of future sea level rise.
The Rise of Dinosaurs
In the Late Triassic and Early Jurassic, 230 to 200 million years ago, dinosaurs expanded from a single lineage to many dozens of lineages, and their range of body sizes grew to include truly gigantic forms. Was this diversification driven by competitive superiority, as widely believed, or did historical contingency play a part? In a Report in the 12 Sep 2008 Science, Brusatte et al. shed new light on this lingering question. The team compared the evolutionary rates and morphological diversity of dinosaurs and their chief "competitors", the crurotarsan archosaurs, which went extinct by the end of the Triassic. Their analysis reveals that during the first 30 million years of their history, dinosaurs lived alongside and shared niches with crurotarsans, who exhibited a greater range of morphology, were often more abundant, and evolved at indistinguishable rates. These findings suggest that the crurotarsans more likely died out by chance than by competitive replacement, and thus cast doubt on the long-standing notion of dinosaur "superiority" and the view that dinosaurs were preordained for success from the start.
Mars’ Magnetic Past
Discovery by the Mars Global Surveyor mission of crustal magnetic fields on Mars indicate that the red planet -- which now has no magnetic field -- once had an active core dynamo. Of particular curiosity is that the crust in the southern hemisphere of Mars is strongly magnetized, but only weakly so in the northern hemisphere. Researchers have also observed major differences in the crustal features in the two hemispheres: The northern hemisphere crust is low, thin, and smooth, whereas the southern hemisphere crust is high, thick, cratered. Now, in a Report in the 26 Sep 2008 Science, Stanley et al. present numerical dynamo modeling studies that may reconcile these two asymmetries. Previous studies assumed that the martian magnetic field was altered over time, after the dynamo stopped operating, but the researchers propose an alternative model in which the dynamo is driven by a hemisphere-scale heat flux pattern. If the heat flow on Mars were lower across the core-mantle boundary in the northern hemisphere, as might be expected from any mechanism producing the crustal dichotomy, then the resulting geomagnetic field generated by circulation in the core might not be a dipole, but be concentrated just in the south (see the related Perspective by B. Langlais and H. Amit; and News story by R. A. Kerr). Such a dynamo would also affect Mars’ atmospheric evolution because only part of the planet would be strongly shielded from the solar wind.
The conventional method of imaging an object is to shine light on it and observe the reflected light. If the object is far away, only a small percentage of the light will be reflected. And if the object is bathed in thermal background light, or noise, enough photons will have to be sent out to discern whether an object is actually there. Now, in a Report in the 12 Sep 2008 Science, Lloyd explains that the strange quantum mechanical phenomenon known as entanglement can be harnessed to detect and image objects far more efficiently -- that is, using much fewer photons -- than existing systems. The Report shows theoretically that if quantum mechanically entangled light is used to probe an object, and one of the photons is kept as a reference, then the ability to detect and image the object is enhanced. The enhancement results from an effective increase in the signal-to-noise ratio. Practical applications of this principle might include improved night-vision systems for the military or safer medical X-rays for patients. An accompanying News story by A. Cho highlighted the study.
In Science Signaling
Skeletal Development Modulator
The extracellular calcium-sensing receptor (CaSR) responds to changes in the concentration of extracellular calcium in the body and modulates various functions of parathyroid cells (PTCs), chondrocytes (the cells that produce cartilage), osteoblasts, and kidney cells. In a Research Article in the 2 Sep 2008 issue, Chang et al. reported that CaSR plays an essential role in embryonic skeletal development, postnatal bone formation, and the differentiation of bone-forming osteoblasts. Through a series of experiments in mice harboring tissue-specific deletion of the Casr gene, the researchers showed that deletion of the receptor in the parathyroid gland and bone results in profound bone defects, whereas deletion in chondrocytes is lethal. Mice in which chondrocyte-specific deletion was induced late in embryonic life were viable but had delayed growth plate development. An accompanying Perspective, E.M. Brown and J.B. Lian noted that the new studies "further clarify the signaling relationships between the parathyroid gland, kidney, and metabolic bone disease in patients with mutations in the gene encoding CaSR…"
-- Miller et al. created an atlas of consensus sequence motifs for 179 kinases and 104 phosphorylation-dependent binding domains that reveals new insight into phosphorylation-dependent signaling (2 Sep 2008)
-- Allen et al. offered a presentation on how engineered fluorescent reporters can be used to follow subcellular activities of signaling components in real time in live cells (16 Sep 2008)
-- Cao et al. showed how the ubiquitin ligase Nedd4 acts through the adaptor protein Grb10 to enhance insulin-like growth factor signaling and control animal growth. (23 Sep 2008)