This Week in Science

Science  06 Jul 2001:
Vol. 293, Issue 5527, pp. 9
  1. Early Warming System

    The periods of climate warming that terminated Quaternary glaciations are commonly understood in terms of Milankovich theory—changes in solar insolation were produced by variations in Earth's orbit around the Sun. However, different regions did not always warm synchronously. Herbert et al. (p. 71; see the Perspective by Lea) present a collection of sea surface temperature records from the California margin for the past 550,000 years. Surface-water warming preceded changes in global ice volume by 10,000 to 15,000 thousand years for each of the past five glacial terminations. These results provide a way to reconcile the climate record from Devils Hole, Nevada, with the idea of orbital forcing, which has been a particularly difficult task for proponents of Milankovich theory.

  2. Twisting Molecules into SETs

    A single electron transistor (SET) comprises a small island with discrete energy levels (a quantum dot or a molecular structure) connected to metallic leads by tunnel junctions. Although some SET configurations have shown room-temperature operation, they have been difficult to control, and so most devices operate at cryogenic temperature. Postma et al. (p. 76) used a scanning probe to form kinks in a metallic carbon nanotube in two places to create the island bracketed by two junctions. The resultant distorted nanotube behaves as a room-temperature SET.

  3. Fully Conjugated Porphyrin Tapes

    Porphryin groups can be assembled into long chains, but these groups still tend to be electronically isolated from one another. Tsuda and Osuka (p. 79) have taken Zn(II) porphyrin oligomers (containing up to 12 groups) and fused the ring system into one large conjugated molecule. The conjugated entity is so large that the electronic absorption bands, which are normally in the ultraviolet-to-visible wavelengths, are pushed down into the near-infrared. Such molecules have a number of potential electronic and optical applications.

  4. Ring Around the World

    The Northern Hemisphere annular mode (NAM), a large-scale pattern of climate variability, is characterized by differences in the strength of zonal winds of opposing directions centered at about 35° and 55°N that dominate climate variability at latitudes between about 20° and 45°N. It affects temperature, rainfall, storm tracks, wind patterns, and the frequency of extreme weather events. Traditionally, the variability associated with this pattern has been thought of as mostly restricted to the North Atlantic and Europe. Thompson and Wallace (p. 85) show that the NAM influences all longitudes of the Northern Hemisphere and that the two modes of the NAM produce characteristic patterns of both mean climate and anomalous weather events.

  5. Cooler Cretaceous Archaea

    During the mid-Cretaceous, about 88 to 155 million years ago, there were periods of exceptional volcanic activity that released so much CO2 into the atmosphere that oceans often became anoxic, possibly through the overgrowth of plankton. When the plankton died and fell to the ocean floor, deep sediments formed that became distinctive black shales recently discovered during the Ocean Drilling Project in the North Atlantic. Kuypers et al. (p. 92; see the Perspective by Smith) have found that the early Albian black shales have the chemical signature of bacterial membrane lipids of chemoautotrophic Crenarchaeota that were adapted to nonhyperthermal environments. This finding pushes back the archaean expansion into cooler climes back by about 60 million years.

  6. Snow Weigh

    Japan has a dense Global Positioning System (GPS) network to monitor changes in surface deformation related to subduction zone-induced earthquakes and volcanic eruptions. Heki (p. 89) shows that seasonal variations in the surface deformation pattern in northeastern Japan are the result of snow accumulation along the western flank of the main mountain range that crosses northeastern Japan. Thus, in order to understand the buildup of strain beneath the island related to the subduction zones, the effect of the snow load needs to be subtracted.

  7. Consequences of Cloning

    The safety of nuclear transfer technologies that have been used to clone animals has been controversial. Humpherys et al. (p. 95) suspected that epigenetic alterations might be responsible for low success rates, even when nuclei from embryonic stem (ES) cells are used. In contrast to normal zygotes that had been transferred to surrogate mothers, cloned mice showed highly variable levels of methylation and expression of imprinted genes. This variability was caused not only by faulty reprogramming during cloning but also reflected a loss of imprinting in the donor cells. However, the survival of animals with clear imprinting abnormalities indicates that they may be more tolerant of such dysregulation during development than had been suspected.

  8. Don't Leave a Wake

    How do large marine predators detect their prey when waters are dark or turbid? Dehnhardt et al. (p. 102; see the news story by Zimmer) found that harbor seals can detect the trails of turbulent water left by escaping prey. Seals accurately followed the hydrodynamic trail left by a small submarine in a pool, apparently by using their sensitive whiskers.

  9. The Tail's Tale

    The normal function of the amyloid-β precursor protein (APP) implicated in Alzheimer's disease is uncertain. Given APP's tantalizing similarities to the cell-surface protein Notch (for example, clipping of both proteins' cytoplasmic tails requires presenilin), Cao and Südhof (p. 115; see the news story by Marx) tested whether APP's cytoplasmic tail might activate transcription. APP's tail in fact formed a multimeric complex with two nuclear proteins, the adapter protein Fe65 and the histone acetyltransferase Tip60. When a heterologous Gal4 or LexA DNA-binding domain was included, the complex could activate gene expression.

  10. Separating Back from Front

    The retinotectal system is a well-studied model for the development of topographic maps with clearly defined neuronal connections in the central nervous system. A prerequisite for retinotectal patterning is the acquisition of positional cues within the developing retina along the anterior-posterior and dorsal-ventral axes. Sakuta et al. (p. 111) identified a molecule, Ventroptin, with a specific expression pattern in the retina that seems to have two different functions. In the dorsal-ventral axis, it prevents dorsalization of the eye by antagonizing bone morphogenetic protein 4 in ventral retinal regions. Along the anterior-posterior axis of the eye, it regulates the expression of ephrin A2.

  11. Vision and Memory

    The prefrontal cortical system is usually associated with working memory. Could other areas involved in much earlier steps of sensory processing also participate in working memory. Supèr et al. (p. 120; see the news story by Helmuth) made recordings in the primary visual cortex (area V1) of awake and behaving monkeys during a delayed-response task. Neuronal activity in area V1 was correlated with performance in a memory task. This neural correlate of working memory seems to be a continuation of the sensory signal processing. The authors propose that contextual modulation in the primary visual cortex is a correlate of the process that forms a bridge between sensory activity and working memory.

  12. A Hepatitis Virus Shows NELF Awareness

    Hepatitis delta virus (HDV) is an RNA virus that increases the pathology associated with the hepatitis B virus. Previous studies have implicated the hepatitis delta antigen (HDAg) in both HDV replication and transcription by the virus' host RNA polymerase II (RNAPII), but the molecular mechanisms are largely unknown. Yamaguchi et al. (p. 124) show that HDAg has a sequence that is similar to the smallest subunit of NELF, a human factor that inhibits transcription elongation by RNAPII. HDAg activates transcription by directly interacting with RNAPII in a NELF-dependent and NELF-independent manner. These findings shed light on the mechanism of action for HDAg in regulating HDV RNA synthesis via RNAPII and may assist efforts in drug design.

  13. Tuning into the Right Channel

    Clustering of signaling proteins in highly ordered complexes continues to be a major theme in studies of signal transduction. Davare et al. (p. 98; see the Perspective by Laporte et al.) report that L-type Ca2+ channels from rat neurons are tightly linked to the β2 adrenergic receptors (β2ARs) that control channel conductance. The authors characterized a signaling complex that contains all of the intermediates for signaling from the receptor to the channel: The β2AR itself, the heterotrimeric guanine nucleotide binding protein Gαss, the adenylyl cyclase activated by the G protein to produce cyclic adenosine monophosphate (cAMP), and the cAMP-dependent protein kinase, which controls the channel through covalent phosphorylation. This close association appears to restrict signaling by β2AR to those channels that are in the receptor complex. Patch clamp recordings from a tiny portion of the cell membrane showed that local application of an agonist (within the pipette) could activate the calcium channel, but that the application of the same stimulus to the rest of cell did not activate the channels within the patch.

  14. NMR Peaks in Messy Magnetic Fields

    The large magnets used in nuclear magnetic resonance are usually augmented by smaller “shimming” fields to create a static homogeneous field. Thus, when smaller mobile magnets are used in certain imaging applications, the inhomogeneity of their fields limits the types of useful information that can be obtained—for example, chemical shift peaks are often so broadened that they cannot be used to determine structure. Meriles et al. (p. 82) adapt a technique (nutation echoes) in which the inhomogeneity of the radio frequency (RF) excitation field roughly matches the inhomogeneity of the static magnetic field. The spin dephasing in the static magnetic field is compensated by a rephasing from the RF field and allows chemical shift information to be preserved. This approach, applied here to multidimensional spectroscopy, could open up several new applications for ex situ imaging.

  15. Of Mice and Men

    One path to a deeper understanding of the diversity and complexity encoded in human DNA lies in comparisons between the human sequence and that of related species. Dehal et al. (p. 104) have sequenced regions of the mouse genome that are related to human chromosome 19. Comparisons revealed evidence for new candidate exons and regulatory elements and the possibility of different controls over the evolution of single genes and clusters. Gene duplication appeared to be associated sites of chromosomal rearrangement.