This Week in Science

Science  02 Dec 2005:
Vol. 310, Issue 5753, pp. 1385
  1. Expedient Cytokine Trafficking


    Phagosomes are formed when cells such as macrophages engulf relatively large particles, like bacteria, from the external milieu. The source of membrane involved in the formation of the phagosome and the ability of other organelles to fuse with the phagosome is a topic of recent controversy. Murray et al. (p. 1492, published online 10 November) describe a fundamental and clever adaptation of phagosomal membrane trafficking in macrophages, whereby recycling endosomes fuse with the newly forming phagosome to create the site for release of tumor necrosis factor—a proinflammatory cytokine involved in innate immunity.

  2. Dating Deep Circulation

    During the transition from the Last Glacial Maximum to the Holocene, a series of changes in the deep-ocean circulation pattern occurred in the North Atlantic. Robinson et al. (p. 1469, published online 3 November) made measurements of the carbon-14 content of the deep-sea coral Desmophyllum dianthus in order to characterize better the changes in circulation of intermediate and deep water in the North Atlantic during that transitional interval. The observed radiocarbon changes in the deep North Atlantic Ocean are consistent with the “bipolar seesaw” model of deep ocean circulation. The greater variability in waters at depths of less than 2500 meters correlates with smaller climate events that occurred near the poles.

  3. Earlier Oxygen Onset?

    Some microbes use the redox reactions of intermediate sulfur compounds as an energy source. These compounds originally formed via oxidation reactions, and thus it has been thought that these microbes evolved after about 1 billion years ago, when the oxygen content of Earth's atmosphere increased and caused a distinctive shift in the main sulfur isotopes (34S/32S) that was recorded in sediments. Johnston et al. (p. 1477) show that including data for 33S isotope in the analysis provides a more accurate signal of microbial sulfur disproportionation. The diagnostic signal emerges considerably earlier than has been thought at about 1.3 billion years ago.

  4. Long After the Quake


    The extending western margin of the Great Basin is one of the more seismically active regions of North America, and four large earthquakes occurred in western Nevada from 1915 to 1954. Gourmelen and Amelung (p. 1473; see the Perspective by Hammond) used radar interferometry to map the continued deformation of this region during the past 10 years and show that the region still seems to be responding slowly to these earthquakes. Consideration of a broad response helps reconcile global positioning satellite data and imply that much of the highly extended crust to the east is now behaving rigidly.

  5. Mercurial Wetting

    The interiors of carbon nanotubes can be filled by liquids through capillary action, but the surface tension of liquid metals such as mercury is too high for the metal to enter the nanotube by this process. Because of this lack of wetting, mercury has been used to form Ohmic contacts to carbon nanotubes. Chen et al. (p. 1480) present evidence for mercury entering open-ended, single-walled carbon nanotubes (SWNTs) by an electrowetting process that is facilitated by the potential drop created when the nanotube is used as a contact. Application of a bias potential changes the force needed to extract the SWNT from a mercury surface, and postmortem transmission electron microscopy indicates that mercury entered the interiors of the SWNTs and also wetted the exterior surfaces.

  6. Bird Heads and Toes

    Archaeopteryx is broadly recognized as the first known bird. It has been represented by nine specimens dating to about 150 million years ago (Late Jurassic). However, these nine specimens are all somewhat incomplete, particularly in important areas of the head and feet. Mayr et al. (p. 1483; see the news story by Stokstad) now describe a 10th specimen that shows new features in these important areas. Its first toe is only partially inverted, and its second can hyperextend. These features, as well as revealed parts of its skull, are notably similar to proposed theropod ancestors to birds.

  7. Heading Off Hearing Impairment

    Congenitally deaf cats and mice show clear abnormalities in the synaptic structure of auditory nerve endings. Are these abnormalities permanent, or could early treatment restore their original function? Ryugo et al. (p. 1490) compared normal hearing, congenitally deaf, and congenitally deaf cats fitted with a cochlear implant system. They investigated anatomical and functional restoration of the auditory nerve synapses; in particular, changes in a structure called the endbulb of Held. The artificial electrical stimulation of the cochlea by the cochlear implant rescued many of the normal features of this synapse.

  8. The Matter of Taste

    The sensation of taste is generated in taste buds, which then send the information through the gustatory nerves to the brain. The neurotransmitter between the taste buds and the nerve had been thought to be serotonin, but mice genetically manipulated to lack functional serotonin receptors sense taste stimuli normally. Finger et al. (p. 1495) have investigated another candidate neurotransmitter that functions at these synapses, adenosine triphosphate (ATP). Mice lacking the two ionotropic receptors for ATP (P2X2 and P2X3) did not show responses to taste stimuli in the gustatory nerves. In addition, these mice could not detect most tastes in behavioral tests in which they had to show preference for one substance over another. These results, considered with the release of ATP from taste buds when they are stimulated, show that ATP is indeed the neurotransmitter at these synapses.

  9. Chromatin and Stem Cells


    Two stem cell types are found in the Drosophila ovary, germline stem cells and somatic stem cells. Self-renewal of these cells requires the function of the Hedgehog, bone morphogenic protein (BMP), and Wingless signaling pathways. Xi and Xie (p. 1487) now show that two adenosine triphosphate-dependent chromatin remodeling factors, Imitation SWI (ISWI) and DOMINO (DOM), also regulate self-renewal in the Drosophila ovary. DOM is required for somatic stem cell self-renewal and ISWI is required for germline stem cell self-renewal in response to BMP signaling in the stem cell microenvironment or “niche.” Because this type of chromatin remodeling complex is highly conserved, it is likely that chromatin remodeling may play a role in stem cell self-renewal in other organisms.

  10. Colon Cancer Connections

    A previously unrecognized connection between two well-known signaling pathways appears to provide a crucial mechanism for control of proliferation of colon cancer cells. Castellone et al. (p. 1504, published online 17 November) show that the EP2 subtype of prostaglandin E2 receptor mounts a two-pronged attack that activates a transcriptional program that favors cell proliferation. When PGE2 binds to EP2, the associated heterotrimeric guanine nucleotide-binding protein (G protein) is activated. The G protein βγ and α subunits act through distinct pathways that converge to promote stabilization and nuclear translocation of β-catenin, a protein that promotes transcription of specific genes that increase proliferation of cancer cells. This signaling system may explain why nonsteroidal anti-inflammatory drugs, which inhibit signaling through PGE2, can at times inhibit development of colon cancer in mice and human patients.

  11. The IgGs Have It

    Different classes of antibody (the immunoglobulins; IgA, IgD, IgE, IgG, and IgM) perform divergent functions within the immune system. IgG has also evolved further into subclasses that vary considerably in their potency in particular types of immune responses. Each IgG subclass possesses a range of binding affinities for the different inhibitory and activating receptors that engage the constant Fc region of the antibody molecule. Nimmerjahn and Ravetch (p. 1510; see the Perspective by Woof) used this observation to construct antibodies bearing the same antigenic specificity combined with the subclass-specific portions of Fc. The ability of these hybrid antibodies to mediate their immunological effects in vivo could be predicted by the strength with which the Fc portion bound the different activating or inhibitory Fc receptor (FcR). Thus, the specificity and strength of FcR binding is a central means by which IgG subclasses determine their dominance in a particular immune response.

  12. Keeping Survivin on Target

    Many proteins are involved in the orchestration of the events required for the successful completion of mitosis. Vong et al. (p. 1499, see the Perspective by Earnshaw) searched for proteins that interact with survivin, a protein that functions in regulation of mitosis and accumulates on condensing chromosomes at the centromeres and later on the spindle. A deubiquitinating enzyme known as hFAM was identified that appears to control localization of survivin and its association with other proteins. Survivin was coupled to ubiquitin through Lys63 linkages, a modification that influences protein-protein interactions, and this modification was necessary for proper binding of survivin to centromeres. Preventing ubiquitination by mutating Lys63 disrupted chromosome alignments and mitotic progression. Thus, enzymes regulating protein ubiquitination appear to have key regulatory roles in controlling the dynamic protein interactions required for proper execution of mitosis.

  13. Not Lost in Translation

    The mammalian translation factor eIF3 (a complex of about 750 kilodaltons) prevents premature association of the large and small ribosome subunits; it is involved in start codon detection; and it assists in the assembly of active ribosomes. In addition, eIF3 recruits messenger RNA (mRNA) bearing either a methylated guanosine cap at the 5′-end or an internal ribosome entry site (IRES) to the small subunit of the ribosome. Using cryoelectron microscopy reconstructions, single-particle analysis, and modeling, Siridechadilok et al. (p. 1513) now elucidate the structure and interactions of eIF3. eIF3 interacts with the hepatitis C virus (HCV) IRES RNA and the 5′-cap binding complex eIF4F via the same domain to position the mRNA strand near the exit site of the 40S ribosomal subunit. This work provides structural insight for translational regulation by eIF3, including the prevention of premature ribosome assembly.

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