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Science Roundup

This month in Science Roundup:

Fateful Decisions
How Clownfish Sing
Bat Aerodynamics
Behavioral Science
Spotlight on Single Molecules
Roadless Space in America
Heat and Slip
Active Eddies
Getting at Mercury’s Core
Single Electrons on Demand
In Science’s STKE

This month’s Science Roundup is sponsored by:

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Fateful Decisions

B and T lymphocytes play a vital role in the body’s defense against pathogens and develop via distinct pathways from the same bone marrow progenitor cells. The signaling component Notch has been identified as a key molecular determinant of whether these progenitors end up as B cells or T cells. Notch signaling in progenitors drives T cell development at the expense of B cell development, but the precise molecular mechanisms that govern this process have been unclear. Now, in a Research Article in the 11 May 2007 Science, Maeda et al. identify a factor that is required to block Notch signaling in bone marrow progenitors, thus allowing them to develop into B cells. The factor is encoded by the proto-oncogene LRF (leukemia/lymphoma-related factor), a gene whose disregulated expression can lead to cancer. The researchers found that mice lacking the LRF gene showed substantially impaired early B cell development, yet were able to produce T cells. LRF-deficient progenitor cells also showed increased expression of multiple Notch-regulated genes. These results suggest that LRF blocks, or least substantially reduces, Notch signaling and may therefore act as a master regulator of B versus T cell fate determination. An accompanying Perspective by I. Maillard and W. S. Pear highlighted the work.

How Clownfish Sing

Scientists have known for decades that clownfish -- small reef-dwelling fish that typically live among the tentacles of sea anemones -- are prolific "singers" capable of making a wide variety of "chirp" and "pop" sounds in the context of reproductive and territorial behaviors. But exactly how the fish make these sounds has remained elusive, largely because they are uttered so quickly. Now, in a Brevia in the 18 May 2007 Science, Parmentier et al. describe the sonic mechanism of the clownfish in considerable detail. Using sound recordings, coupled with high-speed video and x-ray imaging, the team found that sound production requires a coordinated set of movements that includes raising of the head, lowering of the jaw, and a pulling back of the chest bones. As this happens, so-called sonic ligaments at the sides of the jaw are stretched to a snapping point of sorts, at which jaw slams shut. Sound results from the collisions of the teeth, transferring energy to the jaws that are presumably the sound radiator. The authors suggest that this system may have once been part of a feeding mechanism that was later co-opted to produce sound. A related podcast segment highlighted the findings.

Bat Aerodynamics

Birds and bats represent two independent evolutionary paths to achieving the same goal: powered vertebrate flight. While the feathers of a bird wing can be separated on the upstroke to minimize drag and maximize lift, the elastic membranous wings of bats need to generate lift by a different means. In a Report in the 11 May 2007 Science, Hedenström et al. described the unexpectedly complicated flight dynamics of a small, nectar-feeding bat species. With the help of a fog machine and low-turbulence wind tunnel, the researchers studied the vortex wakes -- swirls of turbulent air -- produced by the bats. These flying "footprints" provide clues about the aerodynamic forces generated by the animals’ wings. The observations show that at slow speeds, bats gain lift by flicking their wings backwards and almost upside down. Unlike birds, each bat wing generates its own vortex, and the two are interlinked by vortex structures shed from the body -- a system that may enhance maneuverability. Also, at moderate and high flight speeds, the outer (hand) part of the wing generates negative lift during the upstroke, while the inner (arm) part of the wing generates positive lift. As noted in an accompanying ScienceNOW story by J. Simpson, the results may be useful to the study of engineered flying devices.

Behavioral Science
Special Online Collection

Behavioral science has come of age in recent decades, moving beyond simple studies of rats running in mazes to sophisticated analyses relating to pressing societal issues including understanding terrorism and promoting public health (see the Editorial by A. Leshner in the 18 May issue). Three Review articles, also in the 18 May issue, illustrated how this growing body of research is contributing to our understanding of complex human thought processes and behaviors. Bloom and Weisberg discussed how adult resistance to scientific ideas derives in large part from clashes with common-sense views about the world developed during childhood ( listen to the related podcast segment). Haidt described how the convergence of insights from several fields, including social psychology, neuroscience, and evolutionary theory, have transformed the field of moral psychology. And Niedenthal looked at the embodiment of emotion, which includes the bodily expression of emotion as well as the mental processing of external emotional information. In a related feature, Science Careers explored the evolving fields of neuromarketing and public opinion research, and profiled six behavioral scientists who stepped off the academic path into interesting work in industry, government, and not-for-profit organizations.

Biotech Weed Control

The advent of biotechnology-derived, herbicide-resistant crops has revolutionized farming practices around the globe, contributing to greater productivity with lower costs, reduced pesticide use, and improved farmer health. Perhaps the greatest success story has been that of transgenic crops resistant to glyphosate -- an herbicide prized by farmers for its safety and effectiveness at wiping out hundreds of different kinds of weeds. However, just as pathogens have evolved to outwit antibiotics, weeds resistant to glyphosate are beginning to sprout up and have the potential to wreak serious economic and environmental havoc. In a study in the 25 May 2007 Science, Behrens et al. reported the development of transgenic crops resistant to an alternative herbicide called dicamba, which is widely used, inexpensive, and environmentally friendly. By transferring a bacterial gene for an enzyme that deactivates the herbicide, the team was able to engineer soybeans and other broadleaf plants that proved highly resistant to dicamba. Use of this technology alone or in combination with other herbicide resistance traits will allow rotation of herbicides or use of mixtures of herbicides with the goal of extending their effective lifetimes. A related News Focus by R. F. Service highlighted the work as well as other efforts underway to thwart the proliferation of herbicide-resistant weeds.

Spotlight on Single Molecules
Special Online Collection

In vitro biochemistry and biophysics experiments have taught us much about the dynamic behavior of biomolecules. The ultimate goal of single-molecule research, however, is to understand the spatial and temporal characteristics of single molecules in single cells and to decipher complex molecular mechanisms. A special section of the 25 May 2007 Science highlighted how recent advances in single-molecule techniques are bringing us tantalizingly close to this molecule-scale movie of cellular life. A collection of Review articles discussed insights into protein mechanics made possible by "in silico" approaches, the power of combining molecular cell biology with single-force spectroscopy to explore the complexity cell adhesion, and the physical concepts that have pushed fluorescence microscopy to the nanoscale. In Science’s Signal Transduction Knowledge Environment (STKE), Perspective articles highlighted the application of x-ray crystallography and nuclear magnetic resonance studies, microfluidic technology, and statistical algorithms to the analysis of signaling events at the level of single cells and individual molecules.

Roadless Space in America

The crisscross of roads across the United States -- from local side streets to major interstate highways -- not only offers a convenient means of travel and transport, but access to natural resources and land parcels for development and recreation. But roads can also fragment and destroy wildlife habitats, encroach on watersheds, and contribute to pollution. Monitoring the balance between these ecological costs and societal benefits requires a measure that is relatively scale independent and sensitive to both the number of roads within an area and their distribution. In a Report in the 4 May 2007 Science, Watts et al. introduced a metric called roadless volume (RV), which is derived from the calculated distance to the nearest road in a defined area. Using this measure, the team estimated the amount of roadless space in the 48 contiguous United States, finding that it is unequally distributed by county and further unequally distributed among the population. The county with the lowest per-capita RV turns out to be Kings County in Brooklyn, New York, while the county with the highest per-capita RV is Hinsdale County in southern Colorado. Dr. Watts discussed the work in a related podcast interview.

Heat and Slip

Most earthquakes are caused by fast slip on preexisting faults in Earth’s crust. But geologists have long debated why the friction between rocks does not impede this slippage. In a Report in the 11 May 2007 Science, Han et al. presented results from laboratory experiments on a simulated fault that provide a possible explanation. The team studied friction at high speeds between precut cylindrical bars of Carrara marble and found that thermal decomposition of calcite, the main component of marble, due to localized frictional heating, causes dramatic fault weakening. In other words, heat causes the marble at the sliding fault interface to decompose into fine calcite particles just tens of nanometers in size that effectively lubricate the interface, thus making it more slippery. Although marble is not the typical rock lining actual seismic faults, the results suggest that thermal decomposition may be an important process in the dynamic weakening of faults during earthquakes. As noted in an accompanying Perspective by R. Madariaga, "[t]he work provides new insight into friction at high speeds that may help to solve some long-standing puzzles in earthquake science…"

Active Eddies

Mesoscale eddies -- transient rotating patches of water roughly 100 to 200 kilometers in diameter -- occur throughout the ocean and are thought to play an important role in primary production and biogeochemical mixing. However, their ephemeral nature has made them very difficult to study directly…until now. In the 18 May 2007 Science, two groups report new observations from the Atlantic and Pacific showing that eddies are indeed hotspots of rapid biological rates and geochemical transformations. McGillicuddy et al. measured chlorophyll, diatom abundance, and oxygen in ten eddies in the North Atlantic Ocean’s Sargasso Sea and used a model to show how surface winds could be responsible for the upwelling and associated plankton blooms they observed. Meanwhile, Benitez-Nelson et al. reported the physical and biogeochemical dynamics of a recurrent wind-driven eddy that forms off Hawaii and is associated with a plankton bloom. The team found that although the bloom was highly productive, most of the newly fixed carbon was recycled in the upper water column and not transported to the deep sea as previously assumed. Instead, their results suggest that eddies are a mechanism for preferential removal of silica from upper waters. An accompanying Perspective by A. F. Michaels noted how the new findings may help resolve the differences between estimates of basic ocean properties made at local scales versus estimates that average over whole ocean basins.

Getting at Mercury’s Core

Researchers have been wondering about the state of Mercury’s core for decades. Because Mercury is so small -- its mass is just 5% of Earth’s -- scientists have assumed that the planet cooled rapidly early in its formation, resulting in an object that was solid to its core. But some 30 years ago, scientists discovered that Mercury boasts a global magnetic field. Although it is much weaker than Earth’s magnetic field, the implication is that it is sustained by a similar mechanism -- convective motion in a metallic core that is at least partially fluid. In a Research Article in the 4 May 2007 Science, Margot et al. reported radar measurements showing that the outer core of Mercury, like the outer core of Earth, is indeed molten. The team used a novel technique called radar speckle interferometry -- which involved bouncing radar signals off Mercury and recording them at pairs of radio antennas on Earth -- to probe the planet’s rotation dynamics, including small oscillations in its spin rate (libration). Connections between the planet’s spin axis, wobble about that axis, and orbit suggest that the mantle of Mercury is decoupled from a core that is at least partially molten. S.C. Solomon discussed the new findings, and their implications for understanding Mercury’s thermal history and chemical composition, in a related Perspective and podcast interview.

Single Electrons On Demand

Quantum computing promises to revolutionize information processing as we know it. This is because quantum bits (or qubits) -- the basic elements of quantum computers -- can be encoded in particles such as electrons that can span different quantum states, and thus have the power to simultaneously perform vast numbers of computations at speeds not possible with conventional computers. However, a key hurdle in the realization of quantum computers has been the inability to precisely control the flow of electrons carrying the information. A Report in the 25 May 2007 Science now describes an important step toward this goal. Fève et al. have developed a tiny device that can emit single electrons through a conducting medium called a two-dimensional electron gas (2DEG), and absorb them back again on nanosecond time scales (see the related ScienceNOW story by P. Berardelli). The device consists of a single quantum dot -- a nanometer-sized superconducting crystal -- and a tunnel barrier through which electrons can enter and leave the dot in response to changing the voltage on a nearby control electrode. As noted in an accompanying Perspective by S. Giblin, "[w]ith such a controllable electron source, researchers will now be able to set up one or more electrons in well-defined quantum states, which are crucial for any future quantum computer."

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In Science’s STKE

Keeping the Immune Response in Check

In the human body, switching off a biological process can be just as important as switching it on. Take inflammation, for example. Signals produced to recruit immune cells to a site of infection or to release pro-inflammatory mediators must gradually decrease so that the initial response is controlled and ultimately resolved. In the 1 May 2007 issue of Science’s STKE, four Perspectives highlighted recent insights into how various regulatory mechanisms keep the immune system in check (see the Editorial Guide). Hansell and Nibbs discussed the roles of professional and part-time chemokine "decoys" in the resolution of inflammation, while Hinz and Scheidereit examined how the scaffold involved in activating the transcription factor NF-kappaB also plays a role in terminating the immune response. Vitour and Meurs delved into the regulation of interferon -- a cytokine secreted in response to a variety of stress situations, including viral infection. And Wegener and Krappman looked at the role of CARD-Bcl10-Malt1 signalosomes as pivotal regulators that link not only innate and adaptive immune responses, but also GPCR signaling, to the canonical NF-kappaB pathway.

Also in STKE this month:
--Karnitz and Felts highlighted the role of the chaperone protein Cdc37 in the regulation of the yeast kinome (8 May 2007)
--I. Medina discussed the distinct roles of synaptic and extrasynaptic N-methyl-D-aspartate (NMDA) subtype glutamate receptors in neuronal survival and death (15 May 2007)
--K. Török looked at the effects of calcium signaling on the permeability of the nuclear pore (15 May 2007)
--Dahlberg and Lund discussed the accumulation of the microRNA miR-155 in innate immunity and cancer (22 May 2007)

This month’s Science Roundup is sponsored by: