This Week in Science

Science  16 Nov 2007:
Vol. 318, Issue 5853, pp. 1033
  1. Cockroach Coercion


    Robotics offer new possibilities for studying and modulating animal behavior. Halloy et al. (p. 1155; see the news story by Pennisi) observed collective decision-making by mixed groups of cockroaches and autonomous minirobots. The robots, similar in size (though not in shape) to the cockroaches, were coated in a blend of cuticular hydrocarbons that mimic the natural cockroach cuticle. The robots and the insects made shared decisions regarding choice of shelter, and the robots could modulate the collective decision-making process and produce a behavior pattern—choice of an inappropriate shelter—not observed in groups of cockroaches alone. Thus, a small number of robots can change the global pattern by altering feedbacks between individuals in the system.

  2. Reconstructing Interface Orbitals

    The rich phase diagram of the transition metal oxides and the recent demonstrations of patterning and tuning the interface region, which can lead to unexpected phenomena such as the quantum Hall effect and superconductivity, have generated much interest in developing oxide electronics. Chakhalian et al. (p. 1114, published online 11 October; see the Perspective by Dagotto) now report on an x-ray spectroscopy study on the interface between high-temperature superconducting (Y,Ca)Ba2Cu3O7 and metallic La0.66Ca0.33MnO3 with surface-sensitive as well as bulk-sensitive configurations. Charge transfers from the Mn oxide layer to the Cu oxide layer, but does not simply move into the dz2-x2 orbitals of Cu in a rigid manner. Instead, orbital reconstruction occurs that involves population of the 3z2−12 orbital. Calculations show that the orbital reconstruction is consistent with a scenario in which the Cu atom forms a covalent bond with the Mn atom.

  3. Entropy-Driven DNA Networks

    A key aspect of electronic circuits is amplification or gain, so that low signals can be distinguished from any persistent background. Zhang et al. (p. 1121; see the Perspective by Bar-Ziv) show how gain can be achieved in biochemical circuits. They have designed complex catalytic networks based on DNA in which the output oligonucleotides that are released go on to act as catalysts for other reactions. The process is designed to be entropy driven so that the pathways for reactions are well controlled and can be modified at will. Possible applications lie in the field of catalysis, sensor development, the development of enzyme-free alternative for the polymerase chain reaction, and the construction of nanomachines.

  4. Photonic Route to the High Notes


    Excitation of microstructured optic fibers with intense femtosecond laser pulses can generate broadband white light, and applications range from metrology to the generation of ultrafast pulses of a chosen wavelength. The principles behind white-light generation and optical guidance have not been well understood, and the control of the location and spectral range of the generated light has been limited. Couny et al. (p. 1118) developed theoretical insights into the guidance of light and generation of higher-order modes in the microstructured fibers that has allowed the generation of a frequency comb spanning an extremely wide spectral range with modest input power. The authors discuss how this approach could enable a simplified route to femto- and attosecond pulse generation and arbitrary waveform synthesis.

  5. Equatorial Water on Mars?

    Water on Mars is primarily locked up in the polar ice deposits. Watters et al. (p. 1125, published online 1 November; see the Perspective by Schultz) show that comparable amounts of water could be hidden at the equator in the hills of the Medusae Fossae Formation, which are believed to be formed of volcanic ash and wind-blown sediments. Radar sounding with the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express spacecraft saw reflections from the underlying terrain beneath the sediments that have a dielectric signature consistent with the presence of water ice. If these hills are ice rich, they must contain more dust and sand than the polar layered deposits but could host a volume of water similar to that of the south polar layered deposits.

  6. Megasplay Faults and Tsunami Production

    Tsunamis often result when there is rapid uplift of the sea bed, but their size is very sensitive to the local fault geometry. Megasplay faults, which are long thrust faults that rise from the plate boundary megathrust and intersect the sea floor, are thought to be particularly effective in transferring displacement to the surface. By creating a three-dimensional seismic view of a megasplay fault zone in the Nankai Trough off Japan, Moore et al. (p. 1128) show how such a fault operates and suggest that its slip may have contributed to devastating historic tsunamis such as the 1944 Tonankai event. Similarly, megasplay geometries may affect tsunami generation in subduction zones worldwide.

  7. Spreading the Silence

    The maternal and paternal copies of most genes are generally thought to be expressed at comparable levels, but there are several examples known where this is not the case. Imprinted genes have either the maternal or the paternal allele shut down, and in X-inactivation, one of the two X chromosomes is silenced. A few small classes of genes—including immunoglobulins, T cell receptors, and interleukins—are known to have one or other copy inactivated. Gimelbrant et al. (p. 1136; see the Perspective by Ohlsson) looked across the entire human genome and found that in 5% of analyzed loci either the paternal or the maternal allele is randomly and stably inactivated. This fraction is much higher than had been anticipated.

  8. Cancer's Mutational Landscape


    The genomes of human tumors contain many sequence alterations, a subset of which help drive tumor growth. Wood et al. (p. 1108, published online 11 October; see Perspective by Trent and Touchman) have now undertaken a systematic sequence analysis of >18,000 genes in human breast and colorectal tumors. Depiction of the mutational data on a topographic map indicates that each of these tumor types contains only a few gene “mountains” mutated at high frequency and a much larger number of gene “hills” mutated at low frequency. Importantly, while a large fraction of the mutations driving tumor growth reside in the gene hills rather than the mountains—a finding that underscores the heterogeneity of human cancer—it appears that many of the mutated genes function through cellular signaling pathways that are already well known.

  9. The Yin-Yang of Inflammatory Responses

    Inflammatory responses in the nervous system are very tightly regulated. In particular, T helper 1 type T cell responses must be kept in check, and a potent negative regulator of these cells is the surface receptor TIM3, a member of the T cell immunoglobulin and mucin family. However, Anderson et al. (p. 1141) report the unexpected finding that TIM3 also promotes inflammation through expression on cells of the innate immune system—namely, dendritic cells and microglia of the brain. The opposing roles for the same immune protein when expressed on different populations of immune cells raises intriguing questions about the balance between the promotion and inhibition of tissue inflammation.

  10. Playback During Sleep

    During sleep, hippocampal cells play back sequences of activity recorded beforehand during running of a maze task. Euston et al. (p. 1147) report a similar, although more compressed, form of activity playback, but in the medial prefrontal cortex (mPFC) rather than the hippocampus. The mPFC has been implicated in memory storage and retrieval, and it receives direct inputs from hippocampus.

  11. Spinal Cord Injury and Cortical Compensation

    Neuro-rehabilitation is based on the concept that training recruits intact neuronal systems to compensate for brain injury. However, the neuronal basis of the underlying mechanisms is still poorly understood. Nishimura et al. (p. 1150) carried out a longitudinal study in macaques using a well-defined lesion of the direct cortico-motoneuronal connection at mid-cervical segments of the spinal cord. Functional recovery after lesion of the corticospinal tract involved a variety of widely distributed cortical networks. The contribution of each different cortical region changed depending on the post-operative recovery stage.

  12. Tracking Species Success in the Fossil Record

    Studies of the diversity and distribution of past life on Earth recorded in fossils have usually analyzed genera or families. The fossil record is now rich enough in some areas and for some time intervals to resolve patterns at the level of species and evaluate how the changes compare to those seen at coarser taxonomic levels. Foote et al. (p. 1131) examine the fossil record of marine mollusks in New Zealand since 65 million years ago and specifically their range, or occupancy, across different environments. The overall pattern for many species is surprisingly similar to that of marine invertebrate genera—a gradual rise of occupancy followed by an increased restriction in environments such that many species reach their greatest ecological extent near or somewhat after the midpoint of their temporal or geologic range. For many species, extinction seems to act on those species already in decline.

  13. Mother Knows Best

    Environmental maternal effects have often been speculated to play a role in adaptation. Galloway and Etterson (p. 1134) report that environmental maternal effects are indeed adaptive in a natural population of the herb plant Campanulastrum americanum. Maternal light conditions-whether in light or in shade—cued offspring to express a specific life history schedule—either annual or biennial—that enhanced fitness in local conditions. This mechanism of adaptation may allow more benefits than fixed genetic specialization, especially for sedentary organisms that cannot choose their growth environment, and allow for a flexible response that can change with the prevailing conditions.

  14. Melatonin and Memory

    Long-term memory formation is known to depend on circadian rhythms, but the mechanisms involved remain to be elucidated. Rawashdeh et al. (p. 1144) asked whether the circadian system plays a regulatory role in memory formation in a diurnal vertebrate. Learning of a simple active-avoidance conditioning task in zebrafish was substantially better during the day than at night. This difference was largely the result of the effects of the circadian clock, with the effect on memory formation being mediated by pineal melatonin.