This Week in Science

Science  09 Aug 1996:
Vol. 273, Issue 5276, pp. 715
  1. Nanopores in tubes and through films

    Mesoporous materials can contain porous networks of parallel nanoscale cylinders. Two reports show how such materials can be assembled into hollow structures on the micrometer scale. Lin and Mou (p. 765) tailored the mesoporous aluminosilicate MCM-41 into micrometer-diameter tubules in which its cylindrical pores are coaxial with the tube. Schacht et al. (p. 768) assembled mesoporous films at oil-water interfaces to create hollow micrometer-scale fibers and spheres as well as thin sheets. The pores generally align perpendicular to the film.

  2. American origins

    The eastern margin of North America was first defined in the Precambrian, when rifting created the Iapetus Ocean. Closure of this ocean formed the Appalachian-Ouachita mountains; subsequent reopening formed the Atlantic Ocean. As a result of this history, original fragments of North America are now attached to other continents. Thomas and Astini (p. 752) synthesize recent geologic data to show that one such fragment, originally from the region of the Ouachitas, is now part of western South America. Tracing this connection allows a better understanding of the timing of the formation of the Iapetus Ocean and the past geography of continents.

  3. Solar system origins

    A key for reconstructing events in the early solar system is the recognition of daughter isotopes of short-lived radioisotopes in meteorites. One such important isotope is 26Al, which decays to 26Mg with a half-life of 0.73 million years. Russell et al. (p. 757) searched for the original presence of 26Al in chondrules and calcium-aluminum-rich inclusions (CAIs), two particles that formed early in the solar nebula and are contained in ordinary chondrites, a primitive class of meteorites. The CAIs had the highest amounts of 26Mg, some chondrules had lesser amounts, and some had no evidence of original 26Al. Chondrule formation likely lasted more than 5 million years in the solar nebula.

  4. Delivery systems

    Most neuronal proteins are synthesized in the cell body. Proteins that are required at the synapse must be transported along the axon—many by a process known as slow axonal transport. Terada et al. (p. 784) examined the transport of neurofilament proteins along the axons of living neurons. Their findings suggest that neurofilament subunits can be transported along axonal microtubules, rather than requiring a preexisting neurofilament track for their own transport.

  5. Free to move about the membrane

    The Golgi complex is comprised of a set of flattened cisternae. Many theories have been put forward to explain how the Golgi morphology and the distinctive membrane composition of each cisterna is established and maintained in the face of rapid membrane traffic. Cole et al. (p. 797) examined the lateral mobility of engineered fluorescently labeled Golgi membrane protein in a living cell. Surprisingly, all of the proteins studied showed very rapid movement, which suggests that lateral restriction of diffusion of membrane components is unlikely to explain the distribution of specific Golgi membrane proteins in specific Golgi cisternae.

  6. Drugs, receptors, and hypertension

    Stimulation of alpha2-adrenergic receptors (alpha 2ARs) causes a decrease in blood pressure, and drugs that activate these receptors are widely used to treat hypertension. However, the role of the three alpha2AR subtypes (alpha2a, alpha2b, and alpha2c) and possibly other receptors in the physiological effects of alpha2AR agonists has been unclear. Link et al. (p. 803) and MacMillanet al. (p. 801) describe the specific roles of the alpha2AR subtypes revealed by studies of genetically engineered mice deficient in one of the alpha2AR subtypes. The alpha2a subtype is mainly responsible for the antihypertensive action of alpha2AR agonists, whereas the alpha2b subtype mediates an undesirable opposite, or hypersensitive, effect. Drugs designed to be selective for the alpha2a receptor may be more effective in treating hypertension.

  7. Sending a message

    With so many neurotransmitters activating so many receptors that are coupled to so many second messengers, how do signals overcome the intracellular bureaucracy to produce an effect? Brezina et al. (p. 806) describe a model of combinatorial control of a muscle in the buccal mass of Aplysia. In this system, a relatively small number of identified neurons make it possible to interpret neuromuscular events in terms of behavioral circumstances. The authors were able to predict and confirm experimentally the cellular changes caused by the release of several neurotransmitters, which allows them to explain why, for instance, unpalatable food triggers only a gentle biting, and voracious feeding enforces an increase in muscle relaxation rate.

  8. Pox strategies

    Only two pox viruses have been known to infect humans—variola virus, which was responsible for smallpox, and molluscum contagiosum virus (MCV), which normally causes asymptomatic skin papules but leads to opportunistic infection when it infects persons with AIDS. Senkevich et al.(p. 813) have sequenced the MCV genome and have found important differences in the genes involved in host infection, nucleotide biosynthesis, and cell proliferation. This study not only provides a genetic basis for understanding the very different strategies by which these viruses evade the host immune system but may also provide clues for drug therapies.

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