This Week in Science

Science  30 May 1997:
Vol. 276, Issue 5317, pp. 1309
  1. Familiar old faces

    The origin and evolution of the Neandertals—prominent in Europe during the Pleistocene—and their relation to modern humans has been uncertain. Hominid fossils that may represent the earliest Europeans about 800,000 years ago have been recently found at Atapuerca, Spain. Analysis of about 80 fossil remains by Bermúdez de Castroet al. (p. 1392; see the news story by Gibbons, p. 1331) indicates that the hominids had a face that looked remarkably like that of modern humans. Hominids having a modern face were thought to have evolved, only much later, on the basis of fossils from Africa. The Atapuerca hominids may, thus, have been ancestors to both the Neandertals and modern humans.

  2. Glasses for lithium batteries

    Lithium batteries offer many advantages, including lighter weight, but lithium itself is not used as the anode of rechargeable batteries for safety reasons. Recharging produces microscopic lithium particles that can explode upon contact with oxygen, and anodes in which lithium is intercalated into carbon materials have been used instead. Idota et al. (p. 1395) present the operational characteristics of an alternative anode. A tin-based amorphous oxide was made with a specific capacity for lithium storage that is more than 50 percent greater than that of carbon-based materials after cycles of charging and discharging.

  3. Holey polymers films

    Extending lithographic patterning of electronic devices will require ever finer masks. Park et al. (p. 1401) spin-coated films of diblock copolymers onto a silicon-nitride-coated silicon wafer. The films phase-separated to produce domains of hexagonal arrays of one component polymer surrounded by the other. The array component (polybutadiene) could be selectively removed with ozone, and the resulting mask of polystyrene could be used to etch 20-nanometer holes 40 nanometers apart in the underlying silicon nitride.

  4. Sound and light

    Gas bubbles in water, when hit by ultrasonic waves, can produce bright flashes of visible and ultraviolet light, an effect called sonoluminescence (SL). Such experiments have not been simple to understand and have spawned numerous theories. Moss et al. (p. 1398; see the Perspective by Crum and Matula, p. 1348) present a model of bubbles undergoing SL that can account for its chemical specificity (the bubbles need to contain some noble gas) and the lack of afterglow from these picosecond light pulses. The collapsing bubble produces a shock wave that creates a thermally conducting, partially ionized plasma of ions and electrons. Electrons produce the SL flash, and changes in transparency of the plasma limit the pulse duration. The dynamics are sensitive to bubble size, which could explain the variability of experimental results.

  5. Fibronectin connection

    Uteroglobin (UG) is a secreted mammalian protein found in many tissues, the blood, and the urine. Although UG inhibits inflammation, soluble phospholipase A2, and chemotaxis, its true physiologic function has remained unknown. Zhang et al. (p. 1408) made mice that were deficient in UG and found that they developed severe kidney disease characterized by the deposition of fibronectin (Fn) in the kidney. In vitro studies indicate that UG may normally bind to Fn, thereby preventing the Fn-Fn interaction that is deleterious and initiates kidney damage. These findings may provide insight into a form of human fibronectin-deposit hereditary glomerular disease.

  6. Heartfelt loss

    The myocyte enhancer factor-2 (MEF2) transcription factors bind to a DNA sequence found in cardiac muscle genes and are expressed in the early stages of heart development. Lin et al. (p. 1404) generated mice deficient in one of these factors, MEF2C. The homozygous mutant mice died in utero, and analysis of the mutant embryos revealed severe morphological defects in the heart tube, including the loss of the segment that gives rise to the right ventricle, as well as altered expression of a subset of cardiac muscle genes. These results indicate that MEF2C is a key participant in the regulation of right ventricular development.

  7. Getting a grip

    Cells that are a part of complex tissues, such as capillaries, need to be attached to the extracellular matrix, or they are more prone to die. Is this because the matrix is determining the shape of the cell and the degree that it is stretched out, or is it because the receptors that bind to the matrix (various integrins) are transmitting life-sustaining signals to the interior of the cell when they are engaged? Chen et al. (p. 1425; see the Perspective by Ruoslahti, p. 1345) found that the former is the case. When cells are given precise areas upon which to attach (contact areas), adhesion is important, but if the contact regions of the substrate are broken up to the size of focal adhesions (that contain the integrins on the cell surface) and are spread over a larger area, then DNA synthesis (a measure of cell health) scaled directly with the total cell area and not with the cell-substrate contact area.

  8. Tuberculosis target

    Members of the Mycobacterium genus, which includes the bacterium that causes tuberculosis, are coated with a thick outer cell wall dominated by covalently linked mycolic acids that serve as a protective barrier. Belisle et al. (p. 1420) cloned the enzymes that transesterify mycolic acids and found that they are identical to well-known M. tuberculosis exported proteins called the antigen 85 complex. Interfering with these three enzymes with competitive inhibitors for the substrates in the transesterification reactions inhibited the synthesis of the final mycolic acid cell wall and viability.

  9. Stretched to the limit

    Plant cells are normally confined within the physical limits of a rigid cell wall. However, expansin proteins can induce the cell walls to stretch. Fleming et al. show how the application of expansin, and subsequent relaxation of physical constraints, can affect the development of the meristem. Localized application of expansin to the apical meristem induced formation of new leaflike primordia, suggesting that biophysical forces are a critical element of the developmental process in plants.

  10. Lymph development

    There is little known about the lymphatic system and what regulates its growth. Jeltsch et al. have overexpressed vascular endothelial growth factor (VEGF)-C in the skin of mice and examined the effects on blood and lymph vessels. VEGF-C appears to selectively induce the proliferation of lymphatic but not vascular endothelial cells of the lymphatics, which in turn causes lymphatic vessel enlargement. The selective effects may enable the development of therapeutics to stimulate lymphangiogenesis.

  11. Population dynamics

    A barrier to fully understanding the dynamics of populations has been the inability to reconcile the influences of intrinsic density-regulating mechanisms with those of extrinsic environmental variability. Higgins et al. have used information on the Dungeness crab, for which the life history biology is well known and on which long-term population data are available, to develop a model of population dynamics that includes both components: Stochasticity is built into a deterministic skeleton. Although theoretical models of this kind have been developed before, the predictions of the current model are strikingly similar to observations: Small environmental perturbations generate erratic time-series data. [See the news story by Brown.]

  12. STAT signaling

    The STAT proteins (signal transducers and activators of transcription) associate with receptors on the cell surface. Binding of cytokines, such as interferon (IFN), to these receptors causes phosphorylation and activation of STATs, which move to the nucleus and activate transcription of specific genes. Pfeffer et al. show that STATs have another signaling function. At the IFN receptor, STAT3 binds to the regulatory subunit of phosphoinositide-3 kinase, essentially recruiting that enzyme to the activated receptor. Activation of PI 3-kinase increases the activity of serine/threonine kinases and appears to enhance serine phosphorylation of STAT3, which it requires for full transcriptional activity.

  13. Targets in the brain

    The vertebrate brain is formed by an elaborate interplay of cell proliferation, extension of neuronal processes, and formation of specific synaptic connections. Inoue and Sanes have elucidated some of the signals that direct the development of axons extending out from the chick retina. These axons travel to specific layers of the brain, where they form elaborate axonal arbors. Cell surface molecules regulate the process by which the axons find their chosen layer, and soluble neurotrophic factors regulate the complexity of the terminal arbor within that layer.

  14. Moving viral RNA

    Understanding the mechanism of transport of viral RNA from the nucleus to the cytoplasm of the infected cell is important in studying the replication cycle of the virus and in shedding light on normal cellular processes. Tang et al. found that the constitutive transport element (CTE) of simian retrovirus interacted with a cellular protein, helicase A. Both proteins then moved from the nucleus to the cytoplasm. The role of CTE in exporting RNA was shown to be associated with its ability to bind helicase A.

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