This Week in Science

Science  06 Dec 1996:
Vol. 274, Issue 5293, pp. 1585
  1. Gene expression and memory in the brain

    Different parts of the brain control different types of memory—thus explicit memory, such as of a place, requires the hippocampus and related medial temporal lobe structures, whereas conditioned fear, an implicit memory, requires the amygdala. In order to study how particular genes affect memory formation, it is necessary to be able to control the timing and location of gene expression within the brain. Mayfordet al. (p.1678) combined a forebrain-specific promoter and a tetracyclin transactivator system to control expression of an activated form of calcium-calmodulin-dependent kinase II (CaMKII). Expression of this dominant mutant form of CaMKII in mice led to deficits in hippocampal long-term potentiation (in response to signals in the 5- to 10-hertz range) and in hippocampal-dependent (spatial) memory tasks. These deficits could be reversed by suppression of the transgene. Expression of the transgene only in the lateral amygdyla and the striatum produced a deficit in fear conditioning that could also be reversed at a later stage.

  2. Uplift and melting under Tibet

    The ongoing collision of India with Asia has produced the dramatic uplift of the Himalayas and the Tibetan plateau. Understanding the dynamics of this region requires a view of the collision zone at depth. In a series of five reports in this issue (beginning on p. 1684), an international group of researchers report the results of a geophysical survey of the crust underlying the Tibetan plateau. A variety of seismic and electrical observations suggest that the middle crust beneath perhaps large parts of Tibet contains regions of partial melt. The occurrence of melt may be explained by heating as a result of the collision and can help account for some of the interesting dynamics of the Tibetan plateau and adjacent areas.

  3. Around the bend

    Several factors including bedrock geology, tectonics, and climate interact to control river courses. Stern and Abdelsalam (p. 1696) examine the origin of the Great Bend of the Nile River in northern Sudan using radar imagery and geological mapping. The westward bend reflects the northward flowing segments that follow rock fabrics produced in the Precambrian whereas east-west segments follow Cenozoic faults. Recent uplift in the region may have also led to the westward deflection of the river, forming the great bend.

  4. Nanotube brushes grown on silicates

    Carbon nanotubes consist of concentric shells of graphitic sheets and have diameters in the nanometer range. Controlled production of the nanotubes, both with regard to their length and diameter and their alignment, is important both for potential applications and for detailed characterization of their properties. Li et al. (p. 1701) report a method for producing aligned nanotubes of well-defined length and diameter by using iron particles in mesoporous silica as the catalysts for growing the tubes. Well-aligned arrays of tubes with diameters of 30 nanometers and lengths of 50 micrometers can be grown and can be removed from the substrate to retain aligned tubes.

  5. Protein piracy

    Some DNA viruses, such as herpesviruses, are known to acquire host cell genes. Kaposi's sarcoma-associated herpesvirus (KSHV) is the probable causative agent of KS both in the presence and absence of co-infection with human immunodeficiency virus-type 1 (HIV-1), and Moore et al. (p. 1739) have sequenced KSHV genes that encode four viral proteins similar to two human macrophage inflammatory protein (MIP) chemokines, interleukin-6, and interferon regulatory factor. The virally encoded MIP-1, like the human form, inhibits replication of HIV-1 strains dependent on the CCR5 co-receptor. Such viral gene products may interfere with the host cell's defenses.

  6. Oral autoantigens and diabetes

    One recent approach to combating autoimmune diseases such as rheumatoid arthritis is to induce tolerance in CD4+ T cells by orally administering the autoantigen. Blanas et al. (p. 1707) have found that feeding antigen to mice (in this case, ovalbumin, the “self” antigen in their experimental model of insulin-dependent diabetes mellitus) could produce a cytotoxic CD8+ T cell response that destroyed pancreatic islet cells, a step that could contribute to the onset of autoimmune diabetes. These results indicate that expansion of oral tolerization to other human autoimmune diseases must first consider such potential cytotoxic responses.

  7. Overfed grasslands

    Addition of limiting nutrients to the environment, such as from fertilizers or detergents, can threaten ecosystems; one example is the phosphorus-driven eutrophication of lakes. The last decade has seen a substantial increase in rates of nitrogen deposition from the atmosphere, and a long-term experiment in Minnesota by Wedin and Tilman (p. 1720) suggests a negative impact for grasslands. Loss of biodiversity was associated with the displacement of native slow-growing grasses (a shift from C4 to C3 species), a reduction in the net storage of carbon per additional unit of nitrogen, and a sharp threshold decrease in retention of nitrogen in the soil.