Editors' Choice

Science  10 Jul 2009:
Vol. 325, Issue 5937, pp. 127
  1. Evolution

    Adapting to the Young

    1. Laura M. Zahn
    CREDIT: THAN ET AL., PROC. NATL. ACAD. SCI. U.S.A. 106, 9731 (2009)

    Some human pregnancies result in deleterious immune interactions between the mother and fetus, which are sometimes attributed to genetic incompatibilities between placental cells and the mother's blood. One such interaction is mediated by galectin (above left), a carbohydrate-binding protein that recognizes cell surface molecules on leukocytes. Than et al. find that a cluster of galectin genes on human chromosome 19 shows evidence of having evolved via multiple duplications and rearrangements, and three of these genes are highly expressed at the maternal-fetal interface. This cluster of galectins is present and expressed in the great apes, and in Old World and New World monkeys, but is not found in prosimians (lemurs) or nonprimates. Furthermore, lineage-specific loss and gain of specific gene copies were identified within the monkey and ape clusters, and functional data indicate that differential sugar binding has evolved within the gene cluster. Overall, these findings suggest that the evolution of the long gestational period of humans may have been accompanied by changes in genes involved in maternal-fetal tolerance.

    Proc. Natl. Acad. Sci. U.S.A. 106, 9731 (2009).

  2. Cell Biology

    Energy Makers

    1. Helen Pickersgill

    Mitochondria are the powerplants of most eukaryotic cells; they generate ATP by oxidative phosphorylation, a process mediated by membrane-bound protein complexes. Some of the subunits of these complexes are encoded in the mitochondrial genome, along with a set of transfer RNA (tRNA) genes. The protein mTERF1 is a mitochondrial transcription termination factor, and a mutation in a mitochondrial tRNA (Leu) gene reduces mTERF1 binding to mitochondrial DNA (mtDNA), leading to encephalomyopathy. Wenz et al. show that mTERF2 regulates oxidative phosphorylation by modulating mitochondrial transcription. Knocking out mTERF2 in mice produced memory mistakes and muscle weakness; these two tissues rely on mitochondrial ATP. Cells from these mice expressed lower levels of oxidative phosphorylation–related proteins and also exhibited decreased mitochondrial transcription. mTERF2 binds to mtDNA as well as other mTERF proteins, suggesting a direct role for it in transcriptional regulation.

    Cell Metab. 9, 499 (2009).

  3. Chemistry

    Gold Needles in a Haystack

    1. Julia Fahrenkamp-Uppenbrink
    CREDIT: GONZÁLEZ ET AL., ANGEW. CHEM. INT. ED. 48, 10.1002/ANIE.200901308 (2009)

    Noble metals such as platinum and gold dispersed on oxide supports are widely used as catalysts, and structural characterization of their morphology is crucial to obtaining mechanistic insight. Electron tomography through adapted scanning transmission electron microscopy has yielded three-dimensional images, but the technique relies on contrasting heavy and light elements (so-called Z-contrast, where Z is the atomic number), and so has largely been applied to systems with light supports. González et al. now extend this method to a system with a much smaller atomic number difference, specifically gold particles supported on a ceria-based mixed oxide, a catalyst that may find application in the production of hydrogen for fuel cells. After either oxidative or reductive treatment of the asprepared catalyst, electron tomography revealed the presence of gold particles that were 1 to 3 nm in diameter. The data showed that the support (blue) consisted mainly of octahedral crystallites joined together through numerous nanocrystal boundaries. The particles (yellow) were concentrated at oxide nanocrystal boundaries or stepped sites of the support.

    Angew. Chem. Int. Ed. 48, 10.1002/anie.200901308 (2009).

  4. Chemistry

    Spectral Steering

    1. Jake Yeston

    When a molecule absorbs light, its electrons channel the energy into rearranging their relative positions. The process often entails a rather complex series of subtle movements, and researchers yearn to steer the trajectory with an ever increasing degree of external control. To this end, they have developed sophisticated techniques to modulate the spectral phases and amplitudes of the illuminating pulse, which in turn guide the excitation pathway. Roth et al. show that such coherent control methodology can induce distinct fluorescence behavior in two compounds that possess nearly identical electronic absorption spectra. The molecules in question were flavins that differed by the presence or absence of a phosphate group on a side chain appended to the central aromatic chromophore. The authors applied two sequential excitations, a leading ultraviolet pulse that induced fluorescence and a trailing infrared pulse that quenched it; they then used feedback to discover ultraviolet pulse shapes that either maximized or minimized the depletion ratio of the phosphate-bound to phosphate-free flavin emission. The optimal pulses achieved nearly 30% differentiation in either direction, an effect the authors attribute to the sensitive manipulation of low-frequency vibrational modes along the side chain.

    Phys. Rev. Lett. 102, 253001 (2009).