This Week in Science

Science  22 Aug 1997:
Vol. 277, Issue 5329, pp. 1013
  1. Just as different then as now

    It has been suggested that hominids in the Middle Pleistocene showed greater sexual dimorphism (variation of body size and cranial capacity of men and women) than modern populations, but the comparison has been difficult because the fossil samples are limited and are from different times and places. Arsuaga et al. (p. 1086), thus, analyzed a large collection of hominids (at least 32) from the Sima de los Huesos site in Spain. The analysis suggests that sexual dimorphism was comparable in the modern and ancient populations.

  2. Structures and spins

    Ten years after its discovery, high-temperature superconductivity in copper oxide materials continues to be a complex puzzle. One unifying property is that all of the oxide superconductors are derived from antiferromagnetic insulators; thus the behavior of the copper spins is crucial. Wells et al. (p. 1067) have gone back to the parent compound—oxygen-doped lanthanum copper oxide—to study spin dynamics with neutron scattering. They find a system of spin fluctuations that is incommensurate (length scales different from that of the crystal lattice) and highly robust. The authors point out how the results put strong constraints on theory for these superconductors.

  3. DNA litmus test

    Hybridization assays, which may be used to detect a particular genetic mutation or a pathogen, often make use of radioactive labels. Elghanian et al. (p. 1078; see the news story by Service, p. 1036) have developed an alternative approach for detecting DNA hybridization that takes advantage of the color changes that occur when gold nanoparticles are brought into close contact. Two oligonucleotides bearing 13-nanometer gold particles (one with 13 bases and the other with 15) are hybridized to two halves of the targeted region; the close proximity of the particles leads to a color change from pink to blue. This change is accelerated by freezing the solutions and is visualized with a solid support.

  4. Jumping polymer emission

    Fluorescence microscopy studies of polymer molecules that contain several chromophores reveal jumps in emission intensity that can be attributed to transfer of electronic energy along the polymer chain. Vanden Bout et al. (p. 1074; see the Perspective by Moerner, p. 1059) show that these jumps are not due to spectral diffusion, which has been observed for single molecules and is caused by changes in the spectrum of the molecule. Instead, reversible photochemistry occurs in the polymer that changes the quantum yield for emission. Similar polymers find use in light-emitting diodes, and these results show how a small number of defects could dramatically reduce light emission.

  5. Mycobacteria versus macrophages

    Tuberculosis continues to be a major health threat; it has been estimated that one-third of the world's population is infected with the causative agent, Mycobacterium tuberculosis. Schorey et al. (p. 1091) have found a mechanism by which the bacteria infect macrophages that is specific to the disease-causing mycobacteria. This pathway depends on the association of complement cleavage product C2a with mycobacteria. Identification of this method of invasion could provide new targets for therapies.

  6. Signal and messenger

    Signals received at the terminals of sympathetic neurons are transmitted along extended axons to the nucleus in the cell body. Riccio et al. (p. 1097; see the news story by Barinaga, p. 1037) examined the mechanism by which such a signal is propagated. They developed special culture conditions in which they could apply nerve growth factor (NGF) to the distal processes and terminals of cultured sympathetic neurons and then monitored changes in the activation of the nuclear transcription factor CREB in the cell bodies, which were several millimeters away and not exposed to the growth factor. Activation of CREB in response to NGF applied at the terminals requires transport of the NGF receptor along with its bound ligand to the cell body. Thus, the activated receptor itself appears to be the messenger that carries the signal.

  7. A cautionary tale

    Biological pest control strategies are generally thought to be more environmentally friendly than ones that are chemically based. However, as vividly illustrated by Louda et al. (p. 1088; see the Perspective by Strong, p. 1058), they are not without their hazards. A weevil, introduced from Europe into North America to control thistles that had previously followed the same route, has spread widely geographically and expanded its host range to include many native thistle species, some of which are rare. Stark reductions in seed viability of infected native plants were recorded. As has been seen in other cases, nonindigenous species, once introduced, can be very difficult tocontrol.

  8. Managing methylation

    Methylation of genomic DNA is a widespread phenomenon, but the causes and the effects of such methylation is complex. Jacobsen and Meyerowitz (p. 1100) have identified mutations in Arabidopsis that cause distortions in flower development as a result of changes in transcription of a single gene. The more highly methylated alleles support diminished transcription. Demethylation of these unstable alleles restores normal transcription. In a transgenic line in which genomic methylation as a whole was suppressed, this particular gene still carried excess methylation. Thus, the methylation in the genome may be regulated in several ways, including both specific single-gene decisions and global whole-genome decisions.

  9. The good seeds

    Years of effort in building germplasm banks have built a collection of seeds that represents a great variety of plants, including the traditional crop plants but also including so much more—their wild or weedy relatives and unusual or rare plants not represented in the normal course of agriculture. As discussed by Tanksley and McCouch (p. 1063; see the news story by Mann, p. 1038), these seed banks offer a tremendous resource for the agronomist looking to improve or diversify crops. Recent and ongoing progress in understanding plant genomes makes these germplasm banks even more useful than before, as the power of molecular genetics can be combined with traditional plant breeding.

  10. Iron-reducing bacteria

    Although the geological evidence for microbial Fe(III) reduction in the Archaean Earth is recognized, neither the role of the reduction-effecting organisms nor their identity has been ascertained in biological studies. Liu et al. have discovered thermophilic bacteria that reduce amorphous Fe(III) oxyhydroxide to magnetic iron oxides in geologically and hydrologically isolated Cretaceous- and Triassic-age sedimentary basins in the deep (>860 meters) terrestrial subsurface. These organisms were shown to produce magnetite and maghemite in situ. Molecular analyses based on 16S ribosomal RNA gene sequences revealed that some of these bacteria may represent a previously unrecognized phylogenetic group of dissimilatory Fe(III)-reducing bacteria.

  11. Murchison's cool cloud precursors

    The Murchison meteorite, a well-studied carbonaceous chondrite, contains several organic species with anomalous isotopic ratios which indicate that these components were derived from outside of our solar system. Cooper et al. extracted a series ofsulfonic acids from Murchison and determined the carbon, hydrogen, and sulfur isotope ratios in order to estimate the source and precursor species for these acids. They found deuterium and 33S enrichments that are consistent with the low-temperature environment of an interstellar molecular cloud and suggestive of CS, an abundant species in interstellar clouds, as a precursor to the sulfonic acids.

  12. Mantle minerals in shocked meteorites

    Recently, MgSiO3-ilmenite and possibly MgSiO3-perovskite were found in the shocked veins of the Acfer 040 meteorite; these minerals represented our only natural analogs (although only the Mg-rich end members) for high-pressure mineral phases assumed to be present in Earth's mantle. Tomioka and Fujino have found (Mg,Fe)SiO3-ilmenite and -perovskite phases in the shocked veins of the Tenham meteorite, providing natural analogs for mantle phases that include the important Fe-rich components. These high-pressure and high-temperature mineral assemblages provide natural analogs that will help us understand the properties of the minerals and possible phase assemblages in the mantle, while at the same time help to unravel the mechanism of grain growth under shock conditions and the origin of the meteorites.

  13. Safer superconductors

    High-temperature superconductors with transition temperatures exceeding 120 kelvin contain toxic elements such as thallium and mercury. Chu et al. report on anew family of barium calcium copper oxides with transition temperatures up to 126 kelvinthat exhibit an unusual charge reservoir block.

  14. Clue to cannabinoid signaling

    Anandamide is an endogenous lipid that activates brain cannabinoid receptors. Pharmacologically, it mimics the effects of tetrahydrocannabinol, the active principle of marijuana and hashish. It is present in neurons and is released on depolarization. Beltramo et al. now show the existence of high-affinity transport in neurons and astrocytes (glia). They also identify potent and selective inhibitors of this transport. Theythen show that anandamide inhibitors protect anandamide from physiological inactivation, potentiating and prolonging its effects both in vitro and in vivo. They suggest that thisclass of drugs may provide a means of studying and understanding the roles of the endogenous cannabinoid system and may lead to the development of therapeutic agents that mimic the effects of the cannabinoids.

  15. Seeing signaling

    Through the analysis of mutant phenotypes, the various steps of signaling pathways have been elucidated. Greater insight into the Drosophila ERK (DER) signaling pathway has been gained by a technique used by Gabay et al. A monoclonal antibody directed against the activated form of mitogen-activated protein (MAP) kinase (ERK) was used to monitor the factor's distribution during Drosophila development. Visualization of the in situ activation pattern showed a correlation between the expression of active ERK and the Drosophila epidermal growth factor (EGF) receptor. New information was gained about the EGF receptor pathway, including the temporal and spatial expression of active ERK kinase and the interactions with ligands. This technique may have widespread applicability in various signaling pathways in other organisms. [See the cover.]

  16. Brain tumor model

    Patched (Ptc) is a receptor for the Sonic hedgehog signaling protein and a tumor suppressor that is defective in basal cell nevus syndrome (BCNS). To investigate Ptc function, Goodrich et al. inactivated the ptc gene in mice. Homozygotes died during embryogenesis and displayed severe hindbrain and neural tube defects. Heterozygotes were viable, but a subset developed cerebellar medulloblastomas and skeletal defects resembling those seen in BCNS patients. The heterozygous mice may be a valuable model for studying the etiology of medulloblastoma, a common and often fatal childhood brain tumor.

  17. Bald plants

    A subset of the epidermal cells of plants carry hair-like structures, root hairs in the roots, and trichomes on the leaves and sepals. Wada et al. have found a gene, caprice, in Arabidopsis that affects this aspect of epidermal cell differentiation. Mutants lacking the complete protein have fewer thannormal root hairs, and overexpression of the protein makes the roots extra hairy and theleaves bald. Sequence homology to Myb-like proteins suggests caprice might encode a transcription factor.

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