This Week in Science

Science  21 Feb 2003:
Vol. 299, Issue 5610, pp. 1145
  1. Complex Packing

    The assembly of liquid crystals, surfactants, and block copolymers into organized domains has received a lot of attention because of the variety of structures that form and because of the transitions between different structures driven by small changes in chemistry or concentration. Ungar et al. (p. 1208) have looked at dendrimer-shaped objects and find a liquid crystal phase with tetragonal symmetry. They correlate changes that they see in packing with changes in the chemistry of the exterior units of the dendrimers.

  2. Microwaving Electron Spin

    A practical route to controlling electron spin is critical for the successful development of electronics technology based on spin instead of charge. Although pulsed magnetic fields can manipulate spins, they are not really practical in integrated architectures, where spin information would be created, manipulated, transported between elements, and stored. Kato et al. (p. 1201) show that application of microwave electric fields across a quantum well can be used for the manipulation and time-resolved detection of spin precession in these structures. The obtained effect is similar to that of conventional electron spin resonance but without the need for pulsed magnetic fields.

  3. Large Crystals, Made to Order

    Many biological systems grow patterned single crystals that provide structural support and functionality. Aizenberg et al. (p. 1205; see the Perspective by Douglas) show that they can grow large single crystals of calcite, patterned at the micrometer scale. The micropatterned template is designed to maintain the stability of an amorphous calcium carbonate solution, to initiate crystallization only at select points, and to allow for the removal of water and impurities as the phase transformation from amorphous to crystalline proceeds.

  4. Row Your Metal Ions

    DNA has been used in a variety of ways to connect and fabricate nanostructures. Tanaka et al. (p. 1212) show that a modified DNA base can be used to position metal ions in a row within the helix itself. The modified bases paired only in the presence of Cu2+, through the formation of square-planar complexes that enable the DNA to adopt a right-handed helix. Electron paramagnetic resonance spectra indicate that at cryogenic temperatures, the spins on the Cu2+ ions were aligned in the highest spin state.

  5. Inhaling Information

    Mice rely heavily on pheromones—nonvolatile biochemicals that animals use for communication. By recording from single neurons in a part of the brain called the accessory olfactory bulb while one mouse was interacting with other mice, Luo et al. (p. 1196; see the news story by Miller) found that some neurons responded specifically to male mice, other neurons to female mice, and still others could distinguish members of the same species from those of other species. Thus, the pheromone system allows mice to distinguish essential characteristics of other mice with one sniff.

  6. Forensic Climatology

    It has been suggested that the massive release of methane from marine sedimentary methane hydrates (clathrates) during the Late Pleistocene, accompanying a series of rapid warming events known as interstadials, was responsible for the large increases in the concentration of methane in the atmosphere. Support for this hypothesis, which has been called the “clathrate gun,” has been indirect. Hinrichs et al. (p. 1214) present direct evidence: increases in the concentration of a molecular by-product of prokaryotic methanotrophy in sediments from the Santa Barbara basin. These data show that methane release from these marine sediments occurred during interstadials, linking sudden climate change and submarine methane.

  7. Finding a Full Set of Teeth

    Olduvai Gorge in northern Tanzania is one of the most famous fossil hominid localities and the type locality for Homo habilis. Yet parts of the western Gorge have not been heavily studied. Blumenschine et al. (p. 1217; see the Perspective by Tobias) have discovered a nearly complete maxilla and many tools dating to about 1.8 million years ago. The maxilla is similar to both the type H. rudolfensis, a fossil whose affinity has been debated and that had not been found at Olduvai, as well as H. habilis. The authors suggest that all of these fossils, including what has been considered to be H. rudolfensis, may in fact be H. habilis.

  8. Looking for Like-Minded Partners

    Protein kinases are regulators of many biological processes, but many of the targets of these phosphorylating enzymes remain unidentified. Some proteins have special binding domains that preferentially recognize phosphorylated amino acids, and both the kinases that modify these sites and the binding partners that recognize them look for similar sequence motifs. Elia et al. (p. 1228; see the Perspective by Silljé and Nigg) developed a proteomic screen to identify certain binding domains and used it to search for proteins involved in the control of cell division. The screen revealed a phosphoprotein-binding domain, the Polo-box domain (PBD), itself located in a protein kinase, Polo-like kinase 1 (Plk-1). Further experiments indicated that the PBD promotes subcellular localization of Plk1 and the interaction of Plk1 with its substrates in response to the action of mitotic kinases.

  9. A Lack of Taste

    In 1931, Science published the finding that many individuals are unable to taste phenylthiocarbamide. Now, Kim et al. (p. 1221) have determined the molecular basis of this trait using single-nucleotide polymorphisms to identify a gene associated with taste insensitivity; it encodes a member of the TAS2R bitter taste receptor family. The combination of three polymorphisms within inherited units in the population gives rise to the breadth of variation in tasting ability.

  10. Transgenic Mosquito Fitness

    Evaluating the fitness of transgenic mosquitoes relative to wild-type individuals is a challenging population biology issue that must be addressed to assess the utility of genetically modified mosquitoes for disease control. Catteruccia et al. (p. 1225) have evaluated the combined and individual effects of transposon insertion and exogenous gene expression, as well as the genetic inbreeding of the transformed lines. There were direct costs from the introduced transgene and also a substantial deleterious effect of the mosquitoes' genetic background.

  11. Teeth Times Two

    In vertebrate evolution, two lines of study have indicated that teeth evolved together with jaws or that teeth evolved after jaws. Placoderms represent the most basal clade of jawed vertebrates, and it has been reported that placoderms have tooth-like structures (denticles) that differ from “true” teeth, made of dental lamina, found in other vertebrates. Meredith Smith and Johanson (p. 1235; see the news story by Stokstad) suggest that derived placoderms, arthrodires, exhibited gnathostome-type dentine and that tooth formation and replacement was similar to what has been seen in other jawed vertebrates. Because the teeth are seen in the arthrodires but not in other placoderms, this implies two origins of teeth in jawed vertebrates and is consistent with the separate evolution of jaws and teeth.

  12. How Cells Put on Caps by Themselves

    Cells are generally polarized. How can a single cell, in the absence of external cues, generate a polarized distribution of its constituent parts? Wedlich-Soldner et al. (p. 1231) address this question in the yeast Saccharomyces cerevisiae. Overexpression of the protein Cdc42—a protein known to be involved in polarization of mammalian cells—enabled a cell to polarize spontaneously. It seems that random accumulations of the protein get locked into a process of continued accumulation that arises from a positive feedback in protein localization involving actin-based targeted secretion. This process leads to the formation of a cap of the protein at the cell surface that can then go on to promote the polarization of the cell.

  13. Painful Memories

    Hyperalgesia, the pathological sensitivity to painful stimuli, is poorly understood. Ikeda et al. (p. 1237) have identified the synaptic mechanisms that underlie activity-dependent sensitization of projection neurons in lamina I of the spinal cord. These cells are known to mediate abnormal sensitivity to pain. Induction of synaptic plasticity via pain-encoding peripheral C-fibers required co-activation of NK1 receptors for the neuropeptide substance P, T-type calcium channels, and NMDA receptors, all three of which contributed to a rise in postsynaptic calcium levels. This leads to permanent enhancement of the processing of painful stimuli at the first relay station within the central nervous system.

  14. Perceptual Predisposition

    To what extent does our genetic makeup influence our reaction and response to stimuli or other environmental events? Zubieta et al. (p. 1240) analyzed the contribution of a well-known genetic polymorphism (val158met) in the enzyme catechol-O-methyltransferase to the responses of human subjects to pain and stress. Individuals who are heterozygous differ in terms of brain activity and perceived pain as compared to homozygotes. These results may pave the way for a better understanding of the role of genetics in the mental world.

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