The redistribution of water within and between its major surficial reservoirs continually changes the gravity field of the Earth. Conventional methods can determine annual variations in the gravity field only at a scale of 5000 kilometers or longer, which is still too large to see most regional processes. Tapley et al. (p. 503) present measurements of changes in the gravity field of South America made by the twin Gravity Recovery and Climate Experiment (GRACE) satellites. Their data, with a spatial resolution of 400 km, reveals seasonal peaks of mass in major watersheds of the Amazon and areas to the north. Such measurements are also useful for understanding other processes such as ocean heat storage, sea level rise, polar ice mass accumulation, and groundwater storage.
Norzoanthamine Total Synthesis
The natural product norzoanthamine, which is derived from colonial anemones of the Zoanthus genus, has been shown to have promise not only as an antiosteoporotic drug, but its derivatives can inhibit the growth of murine leukemia cell lines, as well as human platelet aggregation. Miyashita et al. (p. 495, published online 17 June 2004) now report a 39-step total synthesis of norzoanthamine that produces the compound in 3% overall yield. Synthesis of this complex fused ring structure required breaking down the demanding stereochemical requirements into manageable steps.
Animals use public information gleaned from the behavior of other individuals in a wide variety of contexts such as social learning, habitat selection, mate copying, communication, and foraging. A review by Danchin et al. (p. 487) predicts that the emerging public information framework will become a dominant approach in evolutionary studies of many aspects of animal (as well as human) behavior.
Watching the Abyss
The fauna of the deep sea is poorly known, and there are few data offering statistically meaningful links between climate and the abundance of animals on the sea floor, climate and food supply, and food supply and animal abundance in the deep sea. Ruhl and Smith (p. 513) present trends from a 14-year time series from the abyssal depths of the northeast Pacific which show major shifts in community composition that correlate with climate change on time scales similar to pelagic and terrestrial environments. The results corroborate indications that climate fluctuations are influencing deep-sea ecology.
One of the most basic geological process is the incision of bedrock by rivers, yet little is known about the rates or timing of this process along passive continental margins like the eastern seaboard of the United States. Reusser et al. (p. 499) present cosmogenic isotope ages of fluvial bedrock terraces for the glaciated Susquehanna and unglaciated Potomac Rivers, both of which have cut deep gorges along their lower reaches where the river profiles are convex. These gorges formed mostly between 35,000 and 12,000 years ago, much more recently than had been assumed. The coincidence and timing of these episodes lead the authors to suggest that regional geomorphic and climate changes, and not just glacial melting, were responsible for incision.
Just Charge It
Small clusters of atoms that form quantum dots can add or lose a single electron, and this effect can be exploited in devices such as single-electron transistors. How small can a cluster be and still stabilize an added electron? Repp et al. (p. 493; see the Perspective by Horn) show that the dot can be as small as a single atom. They can add or remove a single electron on an individual gold adatom adsorbed on an ultrathin, insulating NaCl film grown on a copper surface by applying a voltage pulse with a scanning tunneling microscope tip. The authors argue that the Au− state is stabilized by the strong ionic polarization on the salt film. The adatom in the Au− charge states diffuses more readily than the neutral atom and moves away from a negatively charged tip. The authors suggest that such charge-state switching could be achieved with electron beam irradiation.
Suffering from Neglect
Ecologists interested in forest succession that occurs on intermediate and long time scales have long wondered why, in the absence of disturbance, forests decline. Wardle et al. (p. 509, published online 17 June 2004; see the cover and the Perspective by Birks and Birks) examined six very different examples of so-called forest retrogression or retrogressive succession in Australia, Sweden, Alaska, Hawaii, and New Zealand. Forest decline was associated with the limitation of phosphorus nutrients over time. Similar patterns of decline occur for forested ecosystems spanning the tropical, temperate, and boreal zones.
This BabA's for You
The gastric bacterium Helicobacter pylori is peculiarly specific to human beings and infects nearly half the population. Decades-long infections can result in gastritis, peptic ulcers, and even cancer. Aspholm-Hurtig et al. (p. 519) have explored the marked biogeography observed in the severity of H. pylori infections in relation to the known ability of the pathogen to bind to the carbohydrates of human blood group antigens. The bacterial adhesin BabA determines blood group binding and governs the distribution of disease prevalence. Amerindian populations, who almost exclusively possess blood group O, and the strains of H. pylori that infect these people exhibit a high frequency of strains that only bind the carbohydrates displayed by this blood group. This finding also explains the high prevalence of peptic ulcer disease in these peoples. The Amerindian strains have derived from European strains within the past 500 years by an attrition of “generalist” bacteria that can also bind to other blood group types.
The benefits of recombinant protein and DNA-based vaccines exist to a large extent in the relative ease and low cost of their production. Similarly, chemical synthesis could allow cheap and large-scale production of carbohydrate-based vaccines for bacterial infections. Verez-Bencomo et al. (p. 522) generated and tested a synthetic oligosaccharide vaccine against Haemophilus influenza type b (Hib), one of the causes of bacterial meningitis. Oligomers of specific length were first produced by using a derivative of the repeating monosaccharide unit of capsular polysaccharide of Hib. These oligosaccharides were covalently attached to tetanus toxoid, which acts as a protein carrier to generate efficient T cell help during the immune response. In clinical trials, the synthetic vaccine provided levels of immunity to Hib infection that were equivalent to the existing vaccine.
The Where and Where of Genetic Variation
Although variations in the number of copies of individual genes in humans have been seen, a map of such variation would be important for genomic studies of disease. Sebat et al. (p. 525) used representational oligonucleotide microarray analysis (ROMA) to generate such a map and show that large-scale copy number polymorphisms are common and widely distributed in the human genome. The largest was over 2 megabases in size. In an analysis of 20 individuals from different geographic backgrounds, variation occurred at least once in 70 genes.
Inhibiting HIV-1 Integration
Among the main modes of therapy used for treating infection with human immunodeficiency virus-type 1, two have proved successful in obstructing the viral life cycle by interfering with virally encoded reverse transcriptase and protease enzymes. A third and rather more elusive target has been the viral integrase, which is required for incorporation of viral DNA into the host genome. Hazuda et al. (p. 528, published online 8 July 2004) successfully used a novel integrase inhibitor to protect macaques from infection with a hybrid simian and human immunodeficiency virus. When the monkeys were either acutely or chronically infected with the virus, the inhibitor strongly suppressed viral loads while allowing significant T cell immunity against the virus.
Epilepsy and Dendritic Ion Channels
Little is known about the changes in ion channel function in the neuronal membrane after a region of the brain has become epileptic. Bernard et al. (p. 532; see the Perspective by Staley) show that the electrical properties of hippocampal pyramidal cell dendrites are altered in a rat model of temporal lobe epilepsy. Back propagation of dendritic action potentials is enhanced in these animals due to a loss of A-type K+ channel function. This change appears ultimately to alter the input-output characteristics of the dendrites that enhance excitability and susceptibility to seizures.
Getting Out of Mitosis
The protein phosphatase Cdc14 controls a number of the late events of mitosis. Cdc14 is sequestered in the nucleolus, but late in mitosis, it is released and moves throughout the cell to help to coordinate the exit from mitosis. Cdc14 is held in the nucleus through interaction with a protein called Net1. Azzam et al. (p. 516) show that release of Cdc14 appears to depend on phosphorylation of Net1 by the master regulator of mitosis, the cyclin B-cyclin-dependent kinase complex.
At the end of the Permian Period (251 million years ago), 90% of marine species disappeared in the largest extinction event in Earth's history. Measurements of the carbon isotopic compositions of marine carbonates and organic material have shown that this event was accompanied by a severe environmental disturbance. Low biological diversity persisted for millions of years into the Triassic, but whether this slow recovery was caused by the natural pace of biological renewal or by unfavorable environmental conditions has been an open question. Payne et al. (p. 506) present a carbon isotopic record of marine carbonate which reveals that there was a period of prolonged instability of the carbon cycle in the Early Triassic that was followed by a sharp transition to carbon isotopic stability from the beginning of the Middle Triassic into the Late Triassic. Thus, the end-Permian extinction was just the first in a series of disturbances that delayed a sustained biological recovery.