This Week in Science

Science  06 Jun 1997:
Vol. 276, Issue 5318, pp. 1473
  1. Sending out the wrong signals

    In the fruit fly Drosophila, the gene transformer controls sexual characteristics. Expression of tra in certain areas of the brain of a male can change his sexual orientation to that of a female. Ferveur et al. (p. 1555) expressed tra selectively in abdominal endocrine cells of Drosophila, the oenocytes, which changed the pheromone profile on the surface of the fly from that of a male (monoenes) to that of a female (dienes). These flies have normal male sexual orientation but elicited inappropriate courtship behavior from other males (as if they were female). These results emphasize the multifaceted nature of the genetic control of behavior.

  2. Our not-so-icy moon?

    When the Clementine satellite was used to bounce radar signals off the moon for detection here on Earth, the signals from the lunar polar regions were suggestive of ice, which perhaps was in shadowed craters. Stacy et al. (p. 1527) have used the Arecibo radar system and detected a radar signal similar to that seen in the Clementine experiment. However, they also mapped the lunar poles at a higher resolution than Clementine and determined that some of the areas that produced the unusual radar signal are in sunlight. Rather than being an ice signature, the authors suggest that the radar signal is due to surface roughness.

  3. Green spectroscopy

    Atmospheric scientists have long observed and used the green nighttime emission at 5577 angstrom wavelength to study the Earth's ionosphere. The source of this emission has been thought to be molecular oxygen ions (such as O2+), which are created by daytime solar ultraviolet exposure but recombine with electrons and dissociate at night. Direct measurement of the recombination processes from different electronic states that might produce the green light has proven difficult. Kella et al. (p. 1530), using an imaging technique at a heavy-ion storage ring, directly measured the yield of oxygen atoms in the 1S excited state from O2+ and found that the yield is greater than theory would predict. This measurement should help to reconcile inconsistencies between atmospheric models and observations for planetary ionospheres of Earth and other planets.

  4. Simpler solitons

    In a nonlinear medium, solitary waves (or solitons) can propagate for long distances yet retain their shape. Conventional models of solitons are mathematically very complex, even more so when soliton interactions such as collisions are involved. Snyder and Mitchell ((p. 1538); see the Perspective by Shen, (p. 1520)) report a model in which the complexity can be radically simplified. With this model, the authors offer a straightforward analysis of soliton collisions. Moreover, they suggest the possibility of a photonic switch in which light is controlled by light.

  5. Visual cortex connections

    A central tenet of visual processing is that neurons in the primary visual cortex respond strongly to lines of a single orientation and weakly or not at all to lines of other orientations. The neurons are grouped by their preferred orientation in columns extending into the deeper cortex, and these columns appear to be arrayed circularly when viewed with optical imaging from above the cortical surface, yielding a pinwheel-like arrangement. The central parts of these pinwheels revealed little orientation-specific activity, suggesting that nonselective neurons might exist. Maldonado et al. (p. 1551) have combined optical imaging with multielectrode recordings to show that the orientation preferences of the columns do project faithfully into the center of the pinwheel, in much the same fashion as the spokes of a wheel meeting at the hub. How the connectivity and selective response of these central neurons are established and maintained still remain to be determined.

  6. Bird evolution

    Archaeopteryx has been one of the key fossils in terms of understanding the early evolution and origin of birds, in part because the fossils are beautifully preserved and also contain dramatic feather imprints. Sanz et al. ((p. 1543); see the news story by Morell, (p. 1501)) describe the fossil of a nestling bird from Spain that contains feather imprints but also provides a clear view of the neck and head. The fossil evidence and comparison with Archaeopteryx implies that the distinctive bird skull did not evolve until late in their evolution.

  7. Self avoidance

    After a pollen grain lands on the flower's stigma, it takes up water and begins the growth process that leads eventually to a fertilized seed unless the pollen and flower are incompatible. Certain species of plants have a self-incompatibility system that ensures that pollen from the same flower cannot function, allowing pollen transported in from other flowers, with a new set of genes, to fertilize the flower. Thus, the problems caused by excessive inbreeding are kept to a minimum. Ikeda et al. (p. 1564) identified mutations in a protein, MOD, that can suppress self-incompatibility; MOD has features that suggest it may transport water across the cell membrane.

  8. Acid and plants

    Agricultural productivity can be lower in excessively acidic soils, a problem that affects about 40 percent of arable land. Although treatment of the soil can help, another approach is to develop plants with greater tolerance. De la Fuente et al. (p. 1566); see the news story by Barinaga, p. 1497) have demonstrated that transgenic plants carrying a bacterial gene that supports overexpression and release of citric acid are more resistant to one of the problematic aspects of acidic soil—that of excess soluble aluminum.

  9. Patterning liquid crystals

    The miniaturization of electro-optic devices relies heavily on the development of economical, fast, and accurate methods for patterning substrates on a small scale. Liquid crystals, which are used in devices such as flat-panel displays, are prime candidates for such patterning, but their use can require mechanical rubbing steps to achieve alignment. Gupta and Abbott show that by patterning gold surfaces with self-assembled monolayers (SAMs) and filling the space between two such substrates with a suitable liquid crystal, complex liquid crystal structures can be formed depending on the underlying SAM composition. The method involves only two processing steps and allows patterning of areas on scales from millimeters to a few hundred nanometers.

  10. Less bang for the buck

    In elementary chemical reaction steps, LeChatelier's principle would normally predict that greater energy in the reactant molecules would help them overcome the potential barrier and lead to an increase in the amount of products. Not necessarily, according to Craig and Brauman, who studied the chlorine exchange reaction of Cl with ClCH2CN; the negative energy barrier characteristic of such bimolecular reaction in the gas phase leads to a decrease in products. Unlike many other gas-phase reactions that have been studied in such detail, the energy appears to be distributed statistically in the collision complex.

  11. Chitin in ancient fossils

    Chitin is an abundant biological molecule and is found in many organisms, notably arthropods, and it is abundant in the ocean. Chitin has been thought to degrade rapidly in sediments and thus not be preserved in the fossil record beyond a few hundred thousand years. Stankiewicz et al. now show that chitin is present in fossil insects preserved in shales that are nearly 25 million years old. Thus, the primary control on chitin preservation is not time.

  12. Separating silencing from initiation

    Silencing of transcription in Saccharomyces cerevisiae has several links to DNA replication. Fox et al. investigated the role of the protein complex ORC (origin recognition complex) that is required for the initiation of DNA replication in silencing. Transcriptional repression of the silent mating type loci (HML and HMR) is caused by a localized alteration in chromatin structure and requires silencers and a number of protein factors. It was recently observed that silencing at the HML and HMR loci required that the cells pass through the S phase of growth. The authors, in their analysis of budding yeast cells, have shown that passage through S phase was required for silencing of HMR but that they could bypass ORC by tethering a protein called Sir1 to the HMR-E silencer. Thus, the role of ORC in silencing was separable from its role in initiation, and the role of S phase in silencing was independent of the replication initiation at the silencers.

  13. Silent defenses

    Gene silencing in plants is the result of an unusual interaction between endogenous genes that bear sequence similarity to introduced genes. The phenomenon both complicates and is used to advantage in constructing transgenic plants with specific desired properties. Ratcliff et al. have investigated the mechanisms behind this interaction and find that related mechanisms are used by the plant as a natural defense mechanism against viral infection. In that case, gene silencing limits susceptibility to viruses of related sequence.

  14. Twin thoughts

    Many researchers had assumed that, although there are genetic influences on cognitive ability, they would be overwhelmed by individual experiences and environmental influences that occur as a person ages. Twin studies of children, adolescents, and middle-aged adults have cast doubt on that hypothesis. McClearn et al. used an unusual data set of Swedish twins at least 80 years of age to show that, even at an advanced age, there are still considerable genetic correlations. [See the cover and the Perspective by Gottesman.]

  15. Dechlorinating bacteria

    Tetrachloroethene (TCE) is a common solvent that, because of spills and improper disposal, has become a widespread groundwater pollutant. This toxic solvent can be converted to the nontoxic product ethylene by a mixed microbial culture under anaerobic conditions. Using selective and supplemented media, Maymó-Gatell et al. isolated a coccoid bacterium that can completely dechlorinate TCE to ethylene. This bacterium requires the presence of cell products from other organisms in the mixed culture, underscoring the importance of nutritional interactions between anaerobes. This microorganism, which appears to be a novel eubacterium, might have application in detoxifying tetrachlorethene-polluted areas. [See the Perspective by McCarty.]

  16. An unkind cut

    Cells die through a series of carefully orchestrated events called apoptosis. Rudel and Bokoch found that the kinase PAK2 (p21-activated kinase 2) is activated through proteolytic cleavage by caspases (cysteine proteases) during Fas- or ceramide-induced apoptosis. This regulation by cleavage is most unusual for this kinase, which is normally activated by a guanosine triphosphatase. The cleavage removes the regulatory region of PAK2, rendering it catalytically active. When PAK2 is inhibited, morphological changes associated with apoptosis are prevented.

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