Editors' Choice

Science  05 May 2006:
Vol. 312, Issue 5774, pp. 659

    Think Globally, Conserve Locally

    1. Andrew M. Sugden

    Insects are undoubtedly the most diverse multicellular organisms on Earth, yet our understanding of the extent of this diversity is still patchy, and to be able to predict patterns of community structure and local diversity would be important in the context of conservation. Finlay et al. analyzed data for more than 600,000 insect species from a wide variety of localities, and report self-similar patterns of body size distribution, species-area relationships, and abundance distributions at spatial scales ranging from a few hectares (Hilbre Island) to the land surface of the entire planet. The similarity of the observed patterns presents a useful tool for monitoring the status of insect communities in the face of human disturbance (including climate change); deviations from the general patterns, such as an unusual distribution of body sizes in an insect community, could provide useful indicators of local extinctions. — AMS

    Proc. R. Soc. London Ser. B 273, 10.1098/rspb.2006.3525 (2006).


    A Higher Power

    1. Jake Yeston

    Nearly 80 years ago, Born and Oppenheimer showed that during a typical molecular transformation, electronic and nuclear motions can be treated independently of each other. The validity of this Born-Oppenheimer (BO) approximation arises from the nearly 2000-fold mass difference between electrons and protons, which results in the electrons completing their rearrangement before the slower, heavier nuclei begin to move. The approximation provides a mathematically tractable framework for accurate modeling of many chemical reactions (for example, see Nieto et al., Reports, 7 April 2006, p. 86). Although there are a number of well-established cases in which the approximation breaks down, these systems generally involve coupling between electronic and vibrational coordinates, rather than mass variations.

    Takahashi and Takatsuka explore the breakdown of the BO approximation in unusual molecules, of interest in fusion research, which host more massive negatively charged particles in place of electrons. Specifically, they model H2+ analogs in which two protons bind either an antiproton or a muon (a product of nuclear decay ∼200 times heavier than an electron). Using semiclassical trajectory calculations, they find that the error in the approximation scales with the 3/2 power of the light-to-heavy particle mass ratio. This result implies that the BO approximation is valid over a wider mass range than is commonly assumed from a 1/4 power mass dependence that appears in the theory's derivation. The authors further confirm this error-scaling relation by carrying out an analysis of the system's energy based on the same perturbational approach used by Born and Oppenheimer. — JSY

    J. Chem. Phys. 124, 144101 (2006).


    Wrinkles of Life

    1. Brooks Hanson

    A variety of geochemical evidence implies that life evolved on Earth roughly 3.5 billion years ago, yet more direct evidence—specifically, fossils or fossil-derived structures such as stromatolites or alteration pits—is still sparse or disputed in rocks dating several hundred million years closer to the present. Most of the evidence has been found in siliceous oozes or sediments, carbonate rocks, or altered basalt from deep oceanic or hydrothermal settings.

    Noffke et al. have discovered fossil microbial mats in another environment, South African tidal sandstones, dated to ∼3.2 billion years ago. These rocks display wrinkles, layered roll-up structures, and carbon-rich laminations that resemble features seen in modern intertidal sandstones and commonly preserved in much younger rocks. Such structures form as ductile microbial mats are buried. Analysis of the carbon isotope compositions of the laminations further supports their bacterial origin. Concentration of these features at the top of sedimentary sequences formed in shallow water environments suggests that the microbes in the mats may have derived their energy through photosynthesis. — BH

    Geology 34, 253 (2006).


    An Internal Iron Sensor

    1. Gilbert J. Chin

    To a cyanobacterium, photosynthesis is a very important activity. One of the components of the photosystem I (PSI) complex is iron, which can be a limiting nutrient in a marine environment. Consequently, when iron levels are low, Synechocystis makes the iron stress-induced protein A (IsiA) and deploys it in circumferential formation around the valuable PSI centers, where it serves both to enhance the absorption of light and to dissipate excess photoenergy. Dühring et al. describe how, in times of plenty, the expression of isiA is controlled by a 177-nucleotide (nt) RNA, which is called IsrR and is transcribed from the complementary or noncoding strand of isiA. They propose that when iron is abundant, the IsrR RNA binds to the isiA mRNA and targets it for degradation. Because artificially decreasing IsrR levels does not produce an increase in isiA mRNA if enough iron is available, the authors suggest that another control element, such as an attenuator, must exist. In Salmonella, expression of the magnesium transporter MgtA is turned on when internal Mg2+ levels drop, and a critical regulatory element resides in the 5′ untranslated region (UTR) of the mgtA gene. Cromie et al. show that the 200-nt 5′ UTR of mgtA consists of a riboswitch (see also Thore et al., Science Express, 4 May 2006) that adopts a transcription-attenuating, two stem-loop structure when Mg2+ is bound. The 160-nt 5′ UTR region of isiA may harbor an ion- (or iron-) sensor. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 103, 7054 (2006); Cell 125, 71 (2006).


    Exciting the Nucleus

    1. David Voss

    Modern laser sources can generate sufficient intensity to induce nuclear reactions. However, the excitation mechanism is indirect: optical laser photons deliver energy to electrons, creating a plasma, and the electrons in turn heat the nuclei sufficiently to overcome the barrier to fission or fusion.

    Calculations by Bürvenich et al. suggest a plausible approach for direct nuclear excitation, using current and future generations of high-power laser systems emitting at x-ray frequencies. If the nuclei are accelerated to high velocities, the resulting Doppler shift of the laser light in the nuclear reference frame brings the nuclear transitions into resonance with the photon frequencies. This technique would enable nuclear quantum optics studies—analogous to the richly developed field of coherent electronic excitation—and could afford higher precision in measurements of nuclear properties, as well as control and detection. — DV

    Phys. Rev. Lett. 96, 142501 (2006).


    Rendered Powerless by Heme

    1. Stephen J. Simpson

    Malaria represents one of the greatest threats to human health in tropical and subtropical regions. Aside from its direct effects, the Plasmodium parasite causes a general suppression of the immune system.

    Millington et al. observed that mice infected with the rodent-specific strain P. chabaudi were less able to produce antibodies to a third-party antigen. Both in culture and in vivo, parasite-infected erythrocytes inhibited the maturation of dendritic cells, as shown by a reduction in the expression of activation markers. Hemozoin (the product of hemoglobin degradation) was found to impede dendritic cell maturation and, in turn, to reduce the ability to activate naïve T cell responses. During an infection with P. chabaudi, these effects on dendritic cells manifest themselves as a reduction in CD4+ T cell proliferation and migration into B cell-rich regions of the lymph node. The subsequent deficit in T cell-assisted B cell expansion thereby offers an explanation for the reduced antibody production seen in infected mice. — SJS

    J. Biol. 5, 5 (2006).

  7. STKE

    FSH Increases Bone Resorption

    1. Nancy R. Gough

    Osteoporosis, a decrease in bone mass, is a common condition affecting postmenopausal women and is due at least in part to decreased estrogen. Sun et al. show that follicle-stimulating hormone (FSH), a pituitary hormone that regulates estrogen production, has a direct effect on bone mass by stimulating the differentiation and resorptive activity of osteoclasts. The cells that degrade and resorb bone are osteoclasts, whereas osteoblasts are the bone-depositing cells. Mice deficient for FSHβ or the FSH receptor were hypogonadal and exhibited many symptoms of estrogen deficiency, yet had normal bone mass. Heterozygous mice (FSHβ+/−) had a 50% reduction in circulating FSHβ and showed decreased bone resorption, decreased abundance of circulating tartrate-resistant acid phosphatase (a marker of osteoclast activity), and decreased expression of osteoclast markers in bone marrow, all of which are consistent with the observed increase in bone density. In cultured cells, FSH stimulated osteoclastogenesis by stimulating differentiation, but not proliferation, and enhanced the resorptive activity of individual osteoclasts. These results point to a direct estrogen-independent effect of FSH on bone density and a crucial role for this hormone in postmenopausal osteoporosis. — NRG

    Cell 125, 247 (2006).