This Week in Science

Science  11 Jul 2003:
Vol. 301, Issue 5630, pp. 137
  1. A Plethora of Planets?

    The Pulsar B1620-26 in the Messier 4 globular cluster in the Milky Way has both a planetary-mass companion and one of stellar mass. Sigurdsson et al. (p. 193; see the news story by Irion) have used Hubble Space Telescope observations and other data to determine that the stellar-mass companion is a young white dwarf. They put forward a model for the formation of this triplet system in which the various interactions did not destroy the planetary companion but caused it to settle into a wider orbit. Their formation scenario implies that planets may be more common than expected in non-solar-type environments, and that dynamical interactions may actually enhance planetary survival.

  2. Nascent Farms in New Guinea

    Clear signs of the independent development of agriculture have been found in just a few separate locations: The Fertile Crescent in what is now Iraq and Iran, in China, and in up to three locations in the New World. Was there yet another center in New Guinea? Denham et al. (p. 189; see the Perspective by Neumann) settle this question by assembling and documenting a variety of evidence in Kuk Swamp, one of the major areas that has been at the center of the debate. The early inhabitants began modifying the landscape of the swamp about 10,000 years ago. Extensive modifications, including construction of ditches and mounds to improve drainage, and plantings of taro and banana appear not quite 7000 years ago, long before the arrival of other humans.

  3. Moving About Softly

    Crustaceans alternate between a rigid exoskeleton and an internal hydrostatic skeleton. Crabs lose their rigid exoskeleton during each molt, but still move about rapidly with a soft body inflated with water. The flexible cuticle of a newly molted animal cannot by itself support the forces necessary for movement. Taylor and Keir (p. 209; see the cover) experimentally show that crabs switch to a hydrostatic skeleton during molting. As the cuticle hardens, the animal switches back to the rigid exoskeleton. This alternation of skeletal types may be more widespread among arthropods than is generally assumed.

  4. Taking the Pulse of Slow Light

    The storage and retrieval of light in atomic ensembles may find use in long-distance quantum optics and communication (see the Perspective by Scully and Zubairy). The search has been on for systems in which the properties of the storage media, mainly the bandwidth, match that of the information carriers, the photons. Van der Wal et al. (p. 196) now show that they can store light pulses in an ensemble of rubidium atoms and then read out that imprinted information with a second “read” pulse. The detected signals remain correlated even after a delay of several microseconds between the write and read pulses. The implementation of slow light in optical networks, such as in delay lines, will likely require a medium less exotic than those used to date, such as atomic vapors or solids at cryogenic temperatures. Bigelow et al. (p. 200) show that ultraslow and superluminal light propagation can be realized in the mineral alexandrite at room temperature. Moreover, they can switch between the slow and fast propagation by simply changing the wavelength of the excitation light.

  5. Balancing the Chloromethane Budget

    Chloromethane, the most abundant atmospheric halocarbon, is responsible for nearly 20% of chlorine-catalyzed stratospheric ozone destruction, but current atmospheric budgets can identify the sources of only 50 to 75% of chloromethane emissions. Hamilton et al. (p. 206) report a facile abiotic reaction that depends on neither plant species nor ecosystems that can explain chloromethane formation in a variety of terrestrial environments. Pectin, a common structural component of plants, reacts readily with chloride ion to yield chloromethane, and this reaction occurs abiotically at ambient temperatures in senescent and weathering plant material. The authors estimate that this process could be responsible for formation of most, if not all, of the chloromethane needed to close the atmospheric budget, and could also provide the mechanism for release of chloromethane during biomass burning.

  6. Tuning into Pathogens

    The need for rapid detection of pathogens, such as in clinical samples and in food, has acquired a new urgency with the threat of bioterrorism and the emergence of familiar and unfamiliar infectious diseases. Harnessing the exquisite capacity of B cells for pathogen recognition, Rider et al. (p. 213) created a biosensor, named CANARY, that detects low levels of viruses and bacteria in a variety of sample formats. Expression of the calcium-sensitive bioluminescent protein, aequorin, in a B cell line permitted a rapid and highly specific luminescent signal to be generated after pathogen-specific cross-linking of membrane antibodies.

  7. Too Much, Too Soon

    In female mammals, the initiation of ovarian follicular growth is somehow regulated to ensure that mature follicles are produced at each cycle. Castrillon et al. (p. 215) now show that female mice deficient in the Forkhead transcription factor Foxo3a displayed an age-related loss of fertility that was caused by extensive activation of ovarian follicles prior to sexual maturity. These results raise the possibility that accelerated follicular initiation contributes to premature ovarian failure, a common cause of infertility in women.

  8. Can't Stop the Noise

    The determination of electrical noise can be difficult, especially when it occurs at high frequencies. Deblock et al. (p. 203) introduce a general noise-detection technique based on a superconductor-insulator-superconductor tunnel device, which is essentially a sensitive photon detector, and use it to detect the high-frequency noise generated by mesoscopic systems. They determine the noise associated with a Cooper-pair box, an artificial two-level system proposed as a qubit for applications in quantum computation.

  9. A Sticky Situation

    Abnormal interactions between thrombin and platelets can lead to thrombosis or bleeding disorders. Two groups, Celikel et al. (p. 218) and Dumas et al. (p. 222), have determined high-resolution crystal structures of the thrombin-binding domain of platelet receptor glycoprotein Ib α (GpIbα) bound to thrombin (see the Perspective by Sadler). Both structures show interaction of GpIbα with two thrombin molecules (one through exosite I and the other through exosite II), but they differ in the interaction site of thrombin exosite I with GpIba. Dumas et al. suggest that the complexes drive platelet adhesion, via one thrombin molecule binding to receptors on two platelet surfaces. Celikel et al. suggest that thrombin might promote intramembranous clustering of Gp1b signaling complexes.

  10. Pain and Breathing

    The Pre-Boetzinger complex (PBC) is a region in the lower brainstem that generates and controls spontaneous breathing movements. Manzke et al. (p. 226; see the p. news story by Couzin) used immunocytochemistry and single-cell polymerase chain reaction analysis to show that serotonin 4(a) [5-HT4(a)] receptors are expressed in respiratory neurons in the PBC. Application of a 5-HT4(a) receptor agonist reduced the respiratory depression evoked by the opioid agonist fentanyl without the loss of its analgesic effect. This effect could be explained by the antagonistic interaction of the two different receptor systems converging on the same intracellular signaling pathway. The absence of 5-HT4(a) receptors in dorsal horn neurons in the spinal cord explains why fentanyl still acts as a pain reliever under these conditions.

  11. Decisions and Goals

    How does the brain decide which action to take out of a large range of immediately available options? Matsumoto et al. (p. 229; see the Perspective by Richmond et al.) recorded from single neurons in the medial and lateral prefrontal cortex of monkeys trained in the selection of motor responses based on current goals. They varied the associations between visual cues, motor action responses, and reward. More medial prefrontal than lateral prefrontal neurons showed activity that reflected a combination of a current motor response and the reward status. Moreover, medial prefrontal neurons showed these effects earlier than lateral prefrontal neurons. The authors suggest that the medial prefrontal cortex contains memories for the action-outcome relation and then evokes an action plan that will achieve the intended goals, or selects one out of many attempted actions based on the current task contingency.

  12. Working Memory and the Premotor Cortex

    What neuronal mechanisms underlie the ability to sequence a series of motor acts? Ohbayashi et al. (p. 233) studied neurons in the premotor cortex of monkeys executing a complex paradigm that involved the memorization of motor sequences and instructional cues for the order of performing the sequence. The authors describe activity related to the sensory aspect of the sequence, the instructional cue itself, the interaction between the instructional cue and the sequence, and both the mnemonic and performance aspects of the task. In total, the neuronal responses in this region appear to convey all of the necessary bits to perform a central element of cognitive-motor behavior. The authors conclude that the premotor cortex is a site where information held in working memory is converted to an arbitrary motor output.

  13. A Double Dose of Trp Regulation

    Amino acid synthesis is tightly controlled in bacteria by a system in which the amino acids themselves, as well as their corresponding transfer RNAs (tRNAs), regulate production. For example, in Bacillus subtilis, the mechanism for regulating tryptophan (Trp) synthesis involves an antiterminator protein called TRAP, which is activated by Trp. However, TRAP activity is antagonized by a protein called anti-TRAP (AT), where the synthesis of AT is induced by uncharged tRNATrp. Chen and Yanofsky (p. 211) now show another level of regulation for the Trp operon in which uncharged tRNATrp also regulates the translation of AT via tandem Trp codons in a leader peptide coding sequence. This mechanism is somewhat reminiscent of the classical Trp attenuation system in Escherichia coli; however, the leader peptide in B. subtilis exerts its effect at the level of translation instead of transcription termination, as seen in E. coli. The authors term the B. subtilis system “regulatory sophistication” because it shows both transcriptional and translational regulation of AT in response to tRNATrp.