This Week in Science

Science  19 Apr 1996:
Vol. 272, Issue 5260, pp. 329
  1. Paleoindian life in the Amazon rainforest

    Sites in North America, such as Clovis, indicate the emergence approximately 11,000 years ago of a culture based on hunting large game over open habitats. Consistent evidence for the situation in South America for this same period has been more difficult to obtain. Roosevelt et al. (p. 373; see cover and the news story by Gibbons, p. 346) surveyed several Amazonian sites and found evidence from a cave campsite for a culture based on tropical floodplain and forest foraging. This site, which appears to have been occupied between 10,000 and 11,200 years ago, revealed finely chipped stone tools and stylized rock paintings.

  2. Clues to continents

    When two oceanic plates collide, one plate is usually forced to subduct beneath the other. Earthquakes and volcanism occur as the plates grind against each other, eventually forming an oceanic island arc. Suyehiro et al. (p. 390) used local seismicity along with a reflection and refraction survey to model the structure of the crust and upper mantle beneath the Izu-Ogasawara island arc. A relatively high velocity granitic zone was found at mid-crustal levels, which suggests that continental crust may be derived from oceanic subducting slabs. Such a mechanism might help explain how continents formed.

  3. Holding fast

    Diamond coatings are desirable on metal and metal carbide parts as hard, wear-resistant coatings, but adherence of such films on these substrates is often poor, in part because the different thermal expansion properties of the coating and the substrate. Singh et al. (p. 396) pretreated the substrate by laser-induced microroughening and improved the adherence of diamond coating as measured by scratch and indentation tests.

  4. Evading NO

    Bacteria that infect a host have their own mechanisms of deflecting the host's defenses. De Groote et al. (p. 414) report that Salmonella typhimurium protects itself from noxious nitric oxide (NO) produced by the cells of infected mice by producing homocysteine. The homocysteine apparently accepts transfer of nitrosonium from S-nitrosothiols, thus diverting NO away from sensitive cellular targets. Mutant bacteria that fail to synthesize homocysteine were more susceptible to NO donor compounds and were less virulent in mice. Accumulation of homocysteine occurs in association with human vascular and neurological disease, and its interaction with signals mediated by NO could represent a mechanism for these effects.

  5. Steroids in plant development

    In animals, steroid hormones are crucial in development, but the physiological role of plant steroids has been unclear. Li et al.(p. 398; see the Perspective by Russell, p. 370) now show that a mutation in the DET2 gene in Arabidopsis, which is similar in sequence to genes for mammalian steroid 5 α-reductases, leads to defects in light-regulated developmental steps. However, the mutants can be rescued by application of the plant steroid brassinolide. These results suggest a role for plant steroids in the transduction of light-mediated developmental signals.

  6. View to a killer

    Homology between the Lag3 gene, which is expressed in activated natural killer (NK) cells and stimulated T cells, and the CD4 gene suggested that its product, LAG3, might be involved in controlling T cell responses. Miyazaki et al. (p. 405) produced Lag3 knockout mice and found that these mice are apparently normal except for defects in the killing of certain target tumor cells by NK cells; the killing of nontransformed cells deficient in major histocompatibility complex class I molecules still occurred. These results suggest multiple NK pathways and that LAG3 acts as receptor or coreceptor for defining these modes.

  7. Histones and transcription

    Modifications of histone proteins bound to DNA are thought to influence the access of transcription factors to regulatory sites in the DNA. Inhibition of histone deacetylase in mammalian cells causes arrest of the cell cycle in G1 or G2 phase. Taunton et al. (p. 408; see the Perspective by Wolffe, p. 371) have purified and cloned the histone deacetylase catalytic subunit from human Jurkat T cells. The predicted protein is similar to RPD3, a transcription factor from yeast. These results help to explain how regulatory modification of histones contributes to transcriptional regulation at specific promoters.

  8. Following a lead

    During development of the vertebrate brain, cortical neurons migrate away from their birthplaces to form the distinctive layers of the mature brain. The neurons follow routes defined by fibers of glial cells. Zheng et al. (p. 417) find that the protein astrotactin, known to aid this guided migration in the cerebellum, is expressed in various parts of the brain where laminar structures are formed by migrating neurons. Astrotactin mediates the interaction between migrating neuron and guiding glial cell fiber.

  9. Links to LTP

    In mammals, stable changes in sensory input can induce changes in the brain itself. The relation between such experience-dependent plasticity and molecular responses to stimulation, such as the long-term potentiation (LTP) seen at individual synapses, has been unclear. Glazewski et al. (p. 421) find that adult, but not adolescent, mice lacking the gene for α-CaMKII, a protein known to be involved in LTP, show less than normal modulation of their cortical response when sensory input from their whiskers is changed, thus linking LTP and experience-dependent plasticity.

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