Editors' Choice

Science  03 Feb 2006:
Vol. 311, Issue 5761, pp. 579
  1. ECOLOGY/EVOLUTION

    Regulating Food Intake

    1. Andrew M. Sugden

    The kakapo—a bulky, ground-dwelling parrot endemic to New Zealand—is one of the world's most endangered birds, with just 83 living individuals. For the past 15 years, conservationists have attempted to increase the population by the supplementary feeding of female birds. However, although ad libitum feeding has indeed improved chick survival, it has also changed the sex ratio of offspring hatched, so that 70% of chicks are male: a proportion clearly at odds with conservation objectives.

    Offspring sex ratio is known to be affected by environmental factors and maternal conditions in predictable ways; in particular, females in good condition tend to produce more sons. Robertson et al. have recently achieved near-parity in offspring sex ratio by regulating the amount of supplementary food given to females as a function of their predicted weight; feeding could not be abandoned entirely, because female kakapo need to weigh more than 1.5 kg in order to breed at all. Thus, the prospects for a conservation program have been enhanced by the application of theory from evolutionary biology. — AMS

    Biol. Lett. 10/1098/rsbl.2005.0430 (2006).

  2. APPLIED PHYSICS

    THz in Practice ...

    1. Ian S. Osborne

    Terahertz (THz) radiation penetrates cloth and plastic to a degree that scales inversely with the frequency. Solid-state laser sources, such as quantum cascade lasers, have been fabricated with energy-level separations tuned for emission toward the high end of the THz regime. However, efforts to lower the frequency, and thereby improve penetration, have been hindered by scattering problems and by reduced out-coupling efficiency as the energy-level spacing approaches the emission linewidth.

    Worral et al. demonstrate a superlattice quantum cascade laser that emits 2-THz continuous wave radiation at an operating temperature of 47 K. They accessed this low-frequency region in part by precise modulation of the aluminum doping level in the GaAs/AlGaAs lasing medium. The result suggests that the emission frequency might be reduced further by careful control of the fabrication and design process. — ISO

    Opt. Exp. 14, 171 (2006).

  3. GENETICS

    A Familial Four-Way Swap Fest

    1. Gilbert J. Chin

    Qualitative advances in technology have made it possible to reexamine an old case, which has led to a heightened appreciation of the fidelity of chromosomal segregation. Over 2 decades ago, a patient with a history of miscarriage was analyzed with classical cytogenetic techniques, yielding evidence of a complex rearrangement involving chromosomes 6, 9, 11, and 20. Later, the mother carried a fetus to term; the adult daughter was determined to carry the same rearrangement and, like the mother, displayed modest levels of the fetal form of hemoglobin [hereditary persistence of fetal hemoglobin (HPFH)].

    Fauth et al. have used multiplex fluorescence in situ hybridization and DNA microarrays to map the precise nature of the rearrangements. They find that the derivative chromosome 6 [referred to as der(6)] possessed by mother and daughter contains portions of chromosomes (chrs) 11 and 20, der(11) carries bits of chrs 6 and 9, der(20) contains portions of chrs 6 and 11, and der(9) harbors multiple pieces from chrs 6 and 11, adding up to a total of 12 breakpoints (one of which coincides with a quantitative trait locus for HPFH) spread over four chromosomes. Nevertheless, these rearranged chromosomes pass faithfully through the pachytene stage of meiosis, when homologous chromosomes pair and form bivalents. — GJC

    Hum. Genet. 10.1007/s00439-005-0103-z (2006).

  4. IMMUNOLOGY

    Primed by Parasites

    1. Stephen J. Simpson

    Collectively, parasites belonging to the genus Leishmania cause extensive mortality and morbidity around the globe. Two major forms of leishmaniasis are characterized by distinct pathologies: a life-threatening visceral disease and a cutaneous form, involving self-healing skin ulcerations. In the latter, resident macrophages and dendritic cells (DCs) of the skin take up the parasite, although in DCs this leads to the priming of Th1 cells that ultimately resolve the disease.

    Woelbing et al. show that unlike macrophages, which use the complement receptor to bind and phagocytose Leishmania promastigotes, DCs acquire the parasite through Fc receptor (FcR)-mediated uptake of complexes comprising antibodies to Leishmania bound to parasitic amastigotes. Without B cells, normally resistant mice became susceptible to disease, as did animals genetically lacking the relevant FcR for IgG binding. In both cases, disease susceptibility was directly attributable to a failure of DCs to prime T cells efficiently and, consequently, to reduced production of IFN-γ. This pivotal role for antibodies to parasites in the priming of T cell immunity by DCs raises the interesting question of how the initial B cell response to the parasite itself develops. — SJS

    J. Exp. Med. 10.1084/jem.20052288 (2006).

  5. CHEMISTRY

    ... and in Theory

    1. Jake S. Yeston

    Terahertz (Thz) radiation, which bridges the infrared and microwave regions of the electromagnetic spectrum, can penetrate most clothing and packaging materials. Researchers have therefore sought to develop THz spectroscopy for security screening, which would require a precise understanding of the absorption spectra that would signal the presence of drugs or explosives. However, the spectra are hard to analyze because they comprise many overlapping modes, arising both from intramolecular vibrations and delocalized lattice motion.

    One approach has been to model the individual molecules computationally, as though they were in the gas phase, in order to discern which spectral features correspond to intramolecular modes, but Allis et al. uncover a problem with this method. Using several variants of density functional theory, they simulate the THz absorption spectrum of crystalline HMX explosive, a solid composed of eight-membered rings with alternating CH2 and N(NO2) groups. Modeling of the isolated molecule fails to reproduce any of the experimental absorption features, whereas more computationally demanding methods, which treat the extended solid lattice, yield reasonable agreement with the measured spectrum. The results suggest that packing forces in the lattice shift the orientation of NO2 substituents and thereby affect intramolecular mode frequencies in addition to lattice modes. — JSY

    J. Phys. Chem. A 10.1021/jp0554285 (2006).

  6. BIOMATERIALS

    Mixing and Matching

    1. Marc S. Lavine

    Strategies for spinal cord injury repair may benefit if a more controlled delivery of drugs to the site of the wound can be achieved. Although bolus injection or a minipump can be used, with the former, the drug may wash away, and a catheter may become blocked or infected. One approach would be to encase the drug in a biodegradable gel that has a viscosity low enough for injection and that gels fast enough to localize to the wound, while being biocompatible and nonadhesive.

    Gupta et al. have designed such a material by combining methylcellulose (MC) and hyaluronan (HA). HA is known to promote wound healing by reducing inflammation and minimizing tissue adhesion. However, it is highly soluble in water and disperses when injected into fluid-filled cavities. MC has inverse gelling properties—that is, it gels as the temperature rises by breaking polymer-solvent bonds and forming hydrophobic junctions. A mixture of 2% HA and 7% MC had a low viscosity and showed fast gelling and suitable degradation characteristics. Intrathecal injection in rats showed that the gel performed as well as or better than artificial cerebrospinal fluid. — MSL

    Biomaterials 27, 2370 (2006).

  7. GENETICS

    Four Score and Nine Generations Ago

    1. Paula A. Kiberstis

    Neurodegenerative disorders vary in their pathologies, but because they all involve cell death, there is the possibility that they share a common mechanism of pathogenesis. One emerging hypothesis posits that the disorders arise because of defects in the intracellular machinery that transports vesicles and proteins.

    Ikeda et al. have studied three families afflicted with spinocerebellar ataxia type 5 (SCA5), a dominantly inherited neurodegenerative disorder characterized by uncoordinated gait and slurred speech. Affected individuals were found to have mutations in the SPTBN2 gene, which encodes β-III spectrin, a cytoskeletal protein that is expressed in Purkinje cells, which are markedly depleted in the brains of individuals with SCA5. β-III spectrin has been implicated previously in protein trafficking, and the mutations may disrupt transport of the neurotransmitter glutamate. Of historical interest, one of the families studied was an 11-generation kindred descended from the paternal grandparents of President Abraham Lincoln. Whether he inherited the SCA5 mutation is unknown, but this discovery may reignite discussions on the ethics of analyzing his DNA. — PAK

    Nat. Genet. 10.1038/ng1728 (2006).