This Week in Science

Science  03 May 2002:
Vol. 296, Issue 5569, pp. 801
  1. In Brevia

    Interactive song playback and microsatellite paternity analysis were used by Mennill et al. (p. 873) to test the hypothesis that female songbirds eavesdrop on male territorial song contests in order to make reproductive decisions.

  2. Avoiding the Obvious

    Chemists usually view elementary chemical reactions as proceeding in a statistical fashion—energy is rapidly redistributed between vibrational and rotational modes, and deep energy minima that lie along the various possible reaction pathways tend to act as a “trap” and dominate product formation. Sun et al. (p. 875) present results for dynamical simulations of a nucleophilic substitution reaction, OH+ CH3F CH3OH + F, which show that despite the presence of a deep minimum in the potential energy surface, more than 90% of the simulation trajectories make their way to products. Product formation appears to occur on a much faster time scale than the competing statistical energy redistribution.

  3. Centimeter Nanotubes

    The fabrication of single-walled carbon nanotubes is still somewhat of an art form, and processes that either create the nanotubes at a much faster rate or of much greater length or purity is still needed. Zhu et al. (p. 884) use an improved floating catalyst method to create centimeter-long single-walled nanotube ropes that are significantly longer than those obtained from either chemical vapor deposition or laser-ablation methods.

  4. Macroscopic Quantum Systems

    Quantum-mechanical effects, such as discrete energy levels and the superposition of energy states, which are normally associated with systems no bigger than the atomic scale, can in fact be observed in certain macroscopic systems. Vion et al. (p. 886) and Yu et al. (p. 889) present results on the formation of two-level macroscopic quantum systems with superconducting tunnel junctions and show that interference effects between the two states can be observed. The realization of such large-scale quantum systems in more readily manipulated macroscopic systems may prove useful in quantum computation (see the Perspective by Leggett).

  5. Phage Forge Nanoparticle Films

    A nanofabrication method is presented that not only forms nanoparticles but also organizes them. Lee et al. (p. 892; see the Perspective by Ober) genetically engineered a coat protein of M13 bacteriophage with a specificity for the surfaces of ZnS nanoparticles. The bacteriophage, being long rigid structures, can form liquid-crystalline phases in solution, and thus the attached nanoparticles can assemble into ordered layered structures.

  6. Antarctic Cooling and Ozone Losses

    Despite an overall global warming trend, temperatures over large parts in the interior of Antarctica have exhibited a small but distinct cooling trend during the past several decades. Thompson and Solomon (p. 895; see the news story by Kerr) present evidence that high-latitude Southern Hemisphere circulation changes during the past few decades reflect a systematic trend in regional atmospheric circulation. Trends in tropospheric circulation trends can be traced to the recent cooling of the lower stratosphere caused by photochemical ozone losses.

  7. Old Family of Flowers

    Fossil specimens of a new family, Archaefructacae, of herbaceous, aquatic plants from the Upper Jurassic to Late Cretaceous Yixian Formation of western Liaoning, China have been characterized by Sun et al. (p. 899; see the cover and the news story by Stokstad). The family consists of a single genus, Archaefructus, with two species, Archaefructus liaoningensis and Archaefructus sinensis. This family, based on molecular and phylogenetic analysis, is one of the basal angiosperms and provides important information about the origin of reproductive organs in flowering plants.

  8. Making Sense of Many Lipids

    Homeostatic mechanisms maintain the lipid composition of biological membranes. In mammalian cells, the sterol response element-binding proteins are transcription factors that regulate cellular levels of cholesterol and fatty acids in a signaling and feedback mechanism that responds to these very lipids. Dobrosotskaya et al. (p. 879; see the Perspective by Nohturfft and Losick) report that this pathway is conserved in flies but also responds to and regulates synthesis of cellular phospholipids, a major membrane lipid.

  9. The Splice of Life

    Although 30 to 50% of human genes produce alternatively spliced transcripts, a much lower percentage is found in yeast. Clark et al. (p. 907) developed a microarray-based system to gain a global view of yeast splicing regulation. The authors examine pre-messenger RNA and messenger RNA levels of all yeast intron-containing genes in response to mutation of splicing-related genes to see what happens to splicing, both globally and at the level of individual transcripts. Cluster analysis indicates which introns behave similarly under certain circumstances and which genes affect splicing in similar ways. This method can be applied to more complex genomes for informative expression profiling of those systems.

  10. Protein Raft Trips

    Attention has been focused on lipid rafts—microdomains of the plasma membrane enriched in sphingolipid and cholesterol—in part because many proteins that take part in signaling across the plasma membrane are preferentially located in these structures. Zacharias et al. (p. 913; see the Perspective by van Meer) studied targeting of proteins to lipid rafts by monitoring fluorescence resonance energy transfer (FRET) between mutants of cyan fluorescent protein (mCFP) and yellow fluorescent protein molecules (mYFP) that had been engineered to prevent the normal dimerization of these proteins. FRET was detected between a fusion protein of CFP with caveolin, which is known to localize to rafts, and YFP that was acylated on its amino terminus. Prenyl modification of YFP, however, did not target the protein to rafts. Thus, lipid modification of proteins can regulate localization, and hence the function, of various proteins in lipid rafts.

  11. Schwann Cells and Nerve Disorders

    The glial cells of the peripheral nervous system, the Schwann cells, play important supporting roles, such as producing myelin, but their generation appears to facilitate two important nervous system disorders. Neurofibromatosis type 1 (NF1) is an inherited disorder characterized by the development of multiple benign tumors in the nervous system (neurofibromas) that occasionally progress to malignancy. Affected individuals have germline mutations in one allele of the tumor suppressor gene NF1, and their tumors show loss of expression of the other allele. Neurofibromas contain a complex mixture of cell types and it has been unclear which of these cells gives rise to the tumors. Using a sophisticated mouse model in which NF1 expression can be selectively ablated in specific cell types, Zhu et al. (p. 884) show that the tumors arise specifically from Schwann cell precursors. Interestingly, however, tumor development was greatly accelerated when the surrounding non-neoplastic cells carried only one functional allele of NF1, illustrating the importance of tumor-host interactions in tumorigenesis. The causative agent of leprosy, Mycobacterium leprae, prefers to infect Schwann cells, and the resulting demyelination of nerve fibers leads to a progressive loss of sensation. It has been assumed that the nerve damage was mediated indirectly by the host's immune responses against the bacteria, but Rambukkana et al. (p. 927; see the Perspective by Brophy) show that the M. leprae directly causes demyelination via a contact-mediated mechanism. Nerve injury stimulates compensatory Schwann cell proliferation, and in this way M. leprae generates more habitable cells to occupy.

  12. Not Keeping Up with Repairs

    Replication of DNA or DNA damage processes can result in double-strand breaks, which in turn may lead to chromosomal translocation and an increased risk of malignancy. Celeste et al. (p. 922) tested the role of the DNA repair-associated protein, H2AX, in maintaining genomic stability. Cells from H2AX-deficient mice displayed several genetic abnormalities, including elevated sensitivity to irradiation-induced damage, chromosomal breakage, and an increased incidence of translocations. Male H2AX−/− mice were infertile due to defective spermatogenesis that resulted from failure of synapsis and meiotic arrest. T and B cell development was also diminished, and B cells displayed defects in switch recombination. Recruitment of DNA repair enzymes was severely affected in the absence of H2AX, confirming a central role for this protein in coordinating the response to DNA damage.

  13. Tackling the Link Between Stress and Alcohol

    The chances to develop alcoholism throughout one's life are determined by a genetic predisposition and an individual's reaction to lifetime events, such as stress. The corticotropin-releasing hormone (CRH) system regulates endocrine responses to stress and mediates stress-related behavior. To better understand the molecular and cellular mechanism underlying stress-induced alcohol drinking Sillaber et al. (p. 931; see the news story by Holden) created knockout mice lacking CRH1 receptors. Crhr1−/− mice did not differ from wild-type mice in their basal alcohol intake and preference. However, after repeated stress episodes, the knockout mice gradually increased their alcohol consumption and kept it elevated for the rest of their life. This change in drinking behavior was accompanied by enhanced protein levels of the NR2B subunit of the N-methyl-D-aspartate receptor.

  14. Populations at a Loss

    If only a few individuals of a once-widespread species remain in an isolated habitat, the species is in fact functionally extinct over most of its range. Hence, the extinction of separate populations is a more accurate reflection of reality. Ceballos and Erhlich (p. 904) present a surrogate measure—decline of range size—based on the spatial distinctness of the most populations. If the area of a species range has been dramatically reduced, it is logical to assume that the species has lost many of its populations. A wide range of mammals—one of the few groups for which sufficient historical data are available—have now dwindled to 50% or less of their historical range.

  15. Sparsely Connected Hubs in Protein Networks

    Genomic and proteomic analyses, combined with accumulated knowledge of cell signaling pathways, are exposing characteristics of the regulatory networks that control physiology. In fact, there is now sufficient detail so that the properties of the networks themselves can be described and analyzed. Maslov and Sneppen (p. 910) examined the protein interaction network described by a systematic screen of yeast protein interactions by the two-hybrid method and also a network of yeast proteins whose regulatory interactions have been genetically defined. In both cases, a relatively small set of proteins are highly connected to other proteins, but these highly connected proteins are primarily connected to proteins with sparse connectivity, not to other proteins that are highly connected. This suppression of interaction of the highly connected nodes in the network has implications for specificity and cross talk in the signaling mechanisms. The authors note that, for reasons not yet clear, the organization of the protein networks is similar to that for interconnection of internet service providers.

  16. Busier Than You Might Think

    How much of a chromosome is transcriptionally active depends on how you look at it. Normally, these regions are mapped by aligning complementary DNA sequences to genome sequences or by annotation, in which a genome sequence is analyzed computationally for coding regions. Kapranov et al. (p. 916) have looked at human chromosomes 21 and 22 with 25-nucleotide probes that were used to detect cytosolic polyadenylated RNA. These probes were spaced either at every base or on average every 35 base pairs. The authors found that, compared with previous estimates, more than an order of magnitude more of the chromosome's sequence is actually used for transcription. They suggest that such transcripts may have been missed for several reasons; for example, they may be too low in concentration for detection in libraries, or are dismissed as contamination.

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