Science Roundup -- The monthly review of Science highlights for AAAS members

This month in
Science Roundup:

A Proven Winner

Special Online Collection: Breakthrough of the Year 2006

Each year, the editors and news staff of Science look back at the big science stories of the past 12 months, and dub one of them the Breakthrough of the Year. In 2006, proof of the Poincaré conjecture -- a century-old mathematics problem that involves explaining the properties of three-dimensional spaces -- won the top honor. As described in a special section of the 22 Dec 2006 Science, the story leading up to and following the proof by Russian mathematician Grigori Perelman is an intriguing one, fraught with controversy and drama. Other shining achievements worthy of runners-up commendation included the sequencing of more than 1 million bases of Neanderthal DNA, confirmation of rapid ice loss from the Antarctica and Greenland ice sheets, genetic insights into macular degeneration, and advances in sub-diffraction limit microscopy. Far less impressive were the Hwang stem cell debacle and other cases of publication fraud given the onerous distinction of "Breakdown of the Year." An assessment of last year’s forecast for advances in 2006 and predictions of fields to watch in 2007 rounded out the special section. On Science Online, each article was accompanied by a set of links to selected papers and relevant Web resources; and a special Breakthrough edition of the Science Podcast looked back at the year’s top stories with several members of the journal’s news staff.

Progesterone and Breast Cancer

Mutations in the breast cancer susceptibility gene BRCA1 greatly increase a woman’s risk of developing breast and ovarian cancers. In its normal form, BRCA1 acts as a tumor suppressor, helping cells repair DNA that might otherwise result in cancer-causing mutations. Now, a Report in the 1 Dec 2006 Science points to another cancer-preventing role for this gene. Poole et al. studied mice deficient in both BRCA1 and p53 -- another tumor suppressor that is frequently mutated in breast cancers -- and found that their mammary epithelial cells accumulated high levels of progesterone receptors and proliferated abnormally. The researchers also reported that treatment with the progesterone-blocking drug mifepristone (RU 486) prevented or delayed mammary tumor development in these mice. The participation of the progesterone receptor in BRCA1-mediated breast cancer could help explain why tumors occur specifically in the breast and ovaries even though the gene is mutated in cells throughout the body; cells outside of these tissues do not carry progesterone receptors. The new results also raise the possibility that antiprogesterone treatment may be useful for breast cancer prevention in individuals with BRCA1 mutations. An accompanying News story by J. Marx highlighted the study.

Cell Signaling Insights

Special Online Collection: Cell Signaling 2006

In the 1 Dec 2006 issue, Science Magazine and its online companion Signal Transduction Knowledge Environment ( STKE ) joined forces to explore new insights into signaling mechanisms that control specific aspects of development and reproduction. Perspective articles in Science highlighted pathways initiated by three different types of receptors: brassinosteroid receptors that control plant size, G protein–coupled receptors that control mating response in yeast, and Notch receptors that control cell fate in animals. The articles were coupled to Connections Maps in STKE’s Database of Cell Signaling. These graphical depictions of signaling pathways and their components include links to relevant literature, data, and background information, allowing users to explore how diverse pathways relate to each other.

The Evolution of Cooperation

The question of how natural selection can lead to cooperative behavior has intrigued biologists for decades. On one hand, evolution is based on fierce competition and should therefore reward only selfish behavior. Yet cooperation is common throughout the biological world, whether between genes or cells or within animal and human societies. In a Review article in the 8 Dec 2006 Science, M. A. Nowak discussed five possible mechanisms for the evolution of cooperation: kin selection, direct reciprocity, indirect reciprocity, network reciprocity, and group selection. And in a related Report, S. Bowles developed a model -- using genetic, climactic, archeological, ethnographic and experimental data -- to help explain the prevalence of altruistic behavior in human societies. According to his analysis, the ecological challenges facing humans during the late Pleistocene resulted in intense competition for resources, frequent group extinctions, and intergroup violence. Members of a group bearing genes for altruistic behavior paid a tax by limiting their reproductive opportunities in order to benefit from sharing food and information, thereby increasing the average fitness of the group, as well as their interrelatedness. Bands of altruistic humans would then act in concert to gain resources from other groups at a time when humans faced daily challenges to survival. An accompanying Perspective by R. Boyd considered how these views fit with other hypotheses about the evolutionary processes that spawned our uniquely cooperative societies.

Invisible Distractors

For anyone who works in an office, days are fraught with distractions from the ringing of phones and pagers to the chattering of co-workers. Most of us are able to block out these obvious disruptions, but we also encounter a host of lesser distractions that we may not consciously perceive. In a Report in the 15 Dec 2006 Science, Tsushima et al. investigated the influence of the strength of distracting stimuli on task performance. The team studied volunteers performing a computer exercise and found that fleeting visual distractions that were irrelevant to the exercise impaired the volunteers’ performance more than easily noticeable distractors did. Simultaneous brain imaging revealed that the subliminal stimuli activated the visual cortex more than the obvious stimuli. However, these fleeting distractions only weakly activated the lateral prefrontal cortex -- a brain region thought to play an important role in inhibiting the influence of irrelevant signals -- whereas the obvious stimuli activated this region more strongly. Thus, weak distractions may disrupt concentration even more than obvious ones because they aren’t noticed by the brain’s filtering system and therefore cannot be effectively blocked out. An accompanying Perspective by P. Stoerig highlighted the Report.

Extreme Nitrogen Fixer

Nitrogen fixation -- the process by which microbes convert molecular nitrogen into more usable ammonia -- is essential to life. In a Report in the 15 Dec 2006 Science, Mehta and Baross described the isolation of a methane-producing archeon from a deep-sea hydrothermal vent that fixes nitrogen at up to 92 degrees Celsius -- thus extending the upper temperature limit of biological nitrogen fixation by some 28 degrees. Like other nitrogen-fixing bacteria and archaea, the newly discovered organism uses a nitrogenase enzyme to tap the vast reservoir of dissolved nitrogen gas present in vent fluids. Phylogenetic analyses indicate that the isolate may be representative of some of the earliest lineages of nitrogen fixation. Given the industrial utility of enzymes with high thermal stability, the discovery may hold great biotechnological potential. As noted in an accompanying Perspective by D. G. Capone, it also has important implications for the extent of life beneath the seafloor, which is likely to be limited by biologically available nitrogen.

A Submarine Eruption Captured

Two-thirds of Earth’s surface is created in eruptions of lava at mid-ocean ridges, yet sea-floor spreading events are poorly understood because they occur far beneath the ocean surface. Now, thanks to well-placed ocean bottom seismometers, researchers have captured the seismic activity associated with a submarine volcanic eruption. In a Report in the 22 Dec 2006 Science (published online 23 Nov), Tolstoy et al. documented the gradual buildup of seismicity for at least 2 years (between 2003 and 2005) leading up to an eruption on the East Pacific Rise, a huge ridge on the ocean floor west of Mexico where two of Earth’s giant tectonic plates gradually spread apart. The long duration of this increase in earthquake activity is unusual compared with volcanoes of this type on land -- where seismic precursors often last only hours to days -- suggesting that it may be possible to forecast similar sea-floor spreading events in the future. The eruption itself was associated with an intense 6-hour peak in seismisicity in January 2006, when magma from the reservoir ~1.4 kilometers beneath the ridge rose to the surface. Unfortunately, two-thirds of the team’s seismic instruments remain stuck in the new lava on the sea floor, but there is hope that more might be rescued. As noted in an accompanying Perspective by W. W. Chadwick Jr. "[d]ata from more instruments would be extremely valuable, allowing us to determine the locations and depths of earthquakes, the three-dimensional distribution of events with time, and the temporal and special variation in earthquake magnitudes."

More Indian Monsoons?

Extreme rainfall events like monsoons can have devastating consequences including landslides, flash floods, and crop destruction. Even more alarming, most climate models have predicted that extreme rainfall events will become more common as global surface temperature increases, though observational evidence of this trend has been scarce. In a Report in the 1 Dec 2006 Science, Goswami et al. analyzed a daily rainfall data set for central India and showed that there has been an increase in the frequency and intensity of heavy rain events (greater than or equal to100 mm/day of rain), and a decrease in the frequency of light to moderate rain events (greater than or equal to 5 mm/day, but less than100 mm/day) during the monsoon seasons from 1951 to 2000. Interestingly, the seasonal mean monsoon rainfall in India has been relatively stable for the past half century. But the researchers point out that this is because the increasing contribution of heavy rain events is offset by the decreasing contribution of lighter rain events. The findings suggest that severe rain events over central India may become more common if global warming continues as expected.

Stardust Treasures

Special Online Collection: Stardust

In January 2004, the Stardust spacecraft encountered comet 81P/Wild 2, passing through the dust cloud surrounding the cometary nucleus and capturing the first dust samples from a planetary body beyond the Moon. The initial analysis of those samples, which were successfully returned to Earth in January 2006, was the subject of a special section of the 15 Dec 2006 issue of Science. A Research Article and six Reports described the physical and chemical characteristics of the cometary particles, most of which are mixtures of silicate materials. Like other comets, Wild 2 is believed to have formed at the frigid outer edges of the solar system. Surprisingly, preliminary examinations have revealed the presence of high-temperature minerals, which indicates that some grains formed close to the Sun and were then transported far out into the solar system before being incorporated into the comet. Two Perspectives detailed how the precious grains were brought back to Earth and what they can tell us about the history of the solar system. And a special video presentation offered additional insights into the significance of the Stardust mission.

Martian Blows and Flows

Launched about 10 years ago, the Mars Global Surveyor spacecraft has served the longest and been the most productive of any mission ever sent to the red planet. NASA lost contact with the spacecraft in early November 2006, but not before its Mars Orbital Camera was able to capture striking new changes to the surface of the planet. In a Research Article in the 8 Dec 2006 Science, Malin et al. reported the discovery of 20 new impact craters between 2 and 150 meters in diameter, that appear to have been created over the last 7 years. Based on the new finds, the researchers calculate that the rate of impact cratering on Mars is comparable to that seen on the Moon. Through repeated imaging of thousands of Martian gullies since 2000, the team may have also found evidence for recent trickles of liquid water. According to their observations, two gullies show a lighter-toned material deposited around obstacles and splayed into numerous branches in ways characteristic of liquid flow. As noted in an accompanying News story by R. A. Kerr the prospect of active gullies and new craters cry out for scientists’ perennial wish for even more data.

DNA Devices

Nucleic acids are best known as the carriers of genetic information, but they are also a versatile material for designing nanometer-scale structures and computational tools. Two Reports in the 8 Dec 2006 Science describe the use of complex DNA pairing and strand-displacement schemes to create a robotic arm and digital logic circuits, both of which could lead to the development more complex nanoscale devices. Ding and Seeman showed that a rotary DNA device that usually operates in solution -- consisting of two DNA strands woven into two pairs of helices with a flexible hinge region in between -- can be mounted within a crystalline DNA lattice and retains its ability to act as a programmable, molecular-scale robotic arm. The result is a nanorobotic system, wherein nanoscale moving parts can be controlled relative to a fixed frame of reference. Seelig et al. designed a set of single-stranded DNA molecules that can be used in a modular fashion to build a series of logic circuits such as AND, OR, and NOT gates, as well as amplifier and threshold gates that protect against noise, signal loss, and leaky reactions. Gate function is entirely determined by base pairing and breaking. An accompanying Perspective by W. Fontana highlighted the Reports.

In Science’s STKE

New Role for a Noncoding RNA

Noncoding RNAs (ncRNAs) control a large range of cellular processes from gene expression to subcellular localization. By now we are very familiar with the ribosomal and transfer RNAs integral to protein translation and the small interfering RNAs and microRNAs involved in the regulation of gene expression. But the world of noncoding RNAs continues to grow both in diversity of classes and diversity of functions. In a Perspective published 12 Dec 2006 in Science’s Signal Transduction Knowledge Environment (STKE), O’Gorman and Akoulitchev discussed a recent study of Drosophila development that demonstrates a novel function for a noncoding region of an mRNA. The mRNA oskar is one of several maternal RNAs important for anteroposterior patterning of the Drosophila embryo. It is normally transcribed in nurse cells that surround the developing oocyte and together in an RNA-binding protein is imported into the oocyte during oogenesis and eventually localized to the oocyte posterior. A series of experiments with Oskar mutants that affect oskar mRNA abundance revealed that that the 3’ untranslated region of this mRNA, and not the Oskar protein, is crucial to the progression of early oogenesis, perhaps by acting as a scaffold for various factors that are targeted to the oocyte. The authors argue that the new finding makes a strong case in favor of new classes of ncRNA, those within an mRNA, being fundamental in the regulation of metazoan development.

Also in STKE this month:

--J. J. Zhao and T. M. Roberts discussed the roles of PI3 kinases in cancer ( 12 Dec 2006 )

--Somoilov et al. looked at the role of noise in vital physiological processes from fluctuations to phenotypes ( 19 Dec 2006 )

--H. M. Pallari and J. E. Eriksson discussed the broad-ranging functions of intermediate filaments of the cytoskeleton ( 19 Dec 2006 )