This Week in Science

Science  03 May 1996:
Vol. 272, Issue 5262, pp. 625
  1. No-passing zone

    Traveling down a two-lane road can be slow, but it is even slower when you are not allowed to pass cars ahead of you. Molecules diffusing in channels so confining that they cannot pass each other are also expected to be slowed down, but this effect has been difficult to measure. Kukla et al. (p. p 702) now provide direct nuclear magnetic resonance measurements of molecules diffusing “single file” in zeolite channels. This type of diffusion may also occur in ion channels in cell membranes.

  2. Peaks in pollution

    Regional data on long-term trends in tropospheric air pollution for the Southern Hemisphere have been extracted from data from the TOMS satellite. Jiang and Yung (p. p 714) compared the TOMS total column ozone values for the high Andes, whose peaks extend through the troposphere, with those of nearby oceanic regions. The derived signals show that tropospheric ozone levels over the tropical Pacific ocean have increased from 1979 to 1992. The likely source of the pollution is biomass burning.

  3. Iron in Io

    Io—the odd, sulfur-rich, volcanically active inner satellite of Jupiter—has a metallic core that accounts for as much as 20% of its mass. Anderson et al.(p. p 709) detected this core using Doppler waves generated by the Galileo orbiter on its closest approach to Io. How this smaller scale version (about the size of the moon) of a differentiated Earth with an iron-rich core evolved and why it is part of the jovian system is still not known.

  4. The layered look

    Suspensions of colloidal particles can form ordered crystals, but this process is difficult to control or to confine to two-dimensional layers on a surface. Trau et al.(p. p. 706) have developed an electrohydrodynamic method for growing two- and three-dimensional colloidal crystals on electrode surfaces. The method can be used with particles from the micrometer- to the nanometer-size range and offers a route for assembling nanoparticles into structures

  5. Imprint by association

    Imprinting is a process that distinguishes certain maternal and paternal chromosomal regions that will be differentially expressed during development. LaSalle and Lalande (p. p.725) found that the maternal and paternal homologs of human chromosome 15 preferentially associate at a region that has been implicated in imprinting (15q11-q13), and that this association occurs only during the late S phase of the cell cycle. This homologous association was not seen in cells from patients with genetic disorders that result from the lack of a paternal or maternal contribution to the 15q11-q13 region (Prader-Willi syndrome and Angelman syndrome, respectively). These results suggest that trans-acting elements may be important in imprinting.

  6. Dendritic spine coupling

    In order to understand how the dendritic spines are electrically and chemically coupled to the dendritic shaft—a process important in understanding synaptic transmission—Svoboda et al. (p. p.716) directly measured the diffusion of dextrans with fluorescence imaging techniques. Their findings show that the spines and shafts are chemically but not electrically separate compartments during neuronal transmission.

  7. Heartsick mice

    Familial hypertrophic cardiomyopathy (FHC) is a clinically diverse inherited disorder whose effects range from mild shortness of breath to heart failure and sudden death. A subset of FHC is caused by mutations in the β cardiac myosin heavy chain (MHC) gene. Geisterfer-Lowrance et al.(p. p.731) created a mouse model of FHC by introducing a clinically defined β cardiac MHC mutation into the mouse α cardiac MHC gene. Mice homozygous for the mutation died 7 days after birth. Heterozygotes survived for 1 year and showed age-dependent hemodynamic and histopathologic abnormalities, with males somewhat more affected than females. Preliminary results suggested that exercise capacity was compromised in the heterozygotes. A special section on cardiovascular medicine (pp. pp.663–693) discusses progress in understanding and treating heart disease.

  8. Broken open

    Extracellular adenosine triphosphate (ATP) can cause the lysis of macrophages due to the formation of large membrane pores in the cell's membrane. The identity of the pore—known as the P2Z receptor—has remained elusive. Surprenant et al. (p.735) describe a bifunctional ATP receptor from rat brain that, in addition to acting as a traditional ligand-gated ion channel, has the characteristics expected of the P2Z receptor—the ability to form lytic pores in cells that express the protein.

  9. Both young and old

    During evolution, new species can arise from the hybridization of two parental species. Rieseberg et al. (p.741; see the Perspective by Coyne,p. 700) examined the genomic composition of an ancient hybrid sunflower species and three hybrid sunflower lines created in the lab. Although the three experimentally created lines were synthesized by different crossing schemes, they contain similar combinations of genes. Surprisingly, these experimentally created lines resemble very closely the ancient hybrid species.

  10. Chick chick duck

    During development of the digits in vertebrates, programmed cell death (apoptosis) causes the loss of interdigital tissue in order to define the digits. Zou and Niswander (p.738) examined the role of the bone morphogenetic protein (BMP) in interdigital apoptosis. The blockage of BMP signal transduction in the developing chick limb by the expression of a dominant negative BMP receptor reduced apoptosis, which resulted in webbed feet as well as a transformation of scales to feathers.

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