This Week in Science

Science  18 May 2007:
Vol. 316, Issue 5827, pp. 949
  1. Rubble Pile in Space


    The Hayabusa spacecraft landed on the Itokawa near-Earth asteroid in 2004 and took crystal-clear pictures of the surface that resolve gravels just centimeters in size. Miyamoto et al. (p. 1011, published online 19 April; see the Perspective by Asphaug) analyzed the surface distribution of the boulders and gravels to document granular processes at work in such a low-gravity environment. The regolith appears to have been sorted by shaking, such that the finest material congregates in areas of lowest local gravity. Clumping of larger rocks suggests Itokawa is also stirred up from below by convection of grains.

  2. Spinning Up New Production


    Mesoscale eddies—transient, rotating patches approximately 100 to 200 kilometers in diameter—occur throughout the ocean and are thought to be important causes of mixing in the upper layers. Plankton blooms are regularly observed to occur within these eddies, which suggests that some of these eddies could be the source of nutrients yet unaccounted in biological production in the subtropics. However, because these eddies are so ephemeral, they have been difficult to characterize experimentally, until now (see the Perspective by Michaels). McGillicuddy et al. (p. 1021) made measurements of chlorophyll, diatom abundance, and oxygen in 10 mode-water eddies in the Sargasso Sea, and used a model that includes an asymmetric response of eddies to surface winds to explain the upwelling and associated plankton blooms that they observed. Benitez-Nelson et al. (p. 1017) took advantage of the characteristic wind patterns around the Hawaiian Islands to make direct biological, chemical, and physical time-series measurements of a large bloom in a recurrent mesoscale eddy there. The bloom was highly productive, but most of the biologically fixed carbon was recycled in the upper water column and not exported to depth, contradicting the assumption that eddies remove carbon from the cycle and promote enhanced sequestration. Their observations do suggest, however, that eddies are a mechanism for preferential removal of silica from upper waters.

  3. Polariton Condensation

    When bosons are packed together such that the density exceeds a critical threshold, and when temperatures are sufficiently low, they can undergo a phase transition and condense into a single quantum state. This Bose-Einstein condensation has been demonstrated in a number of systems, including cold atoms, superfluids, and superconductors. There is a desire, because of the small effective mass (and the potential to drive the phenomenon to higher temperatures) to create condensed states in semiconductor systems. Balili et al. (p. 1007; see the Perspective by Littlewood) show that an ensemble of polaritons, which are quasiparticles formed by photons coupled to excitons, can be generated and trapped in a microcavity in a way analogous to cold-atom traps. The authors then demonstrate the signatures of Bose-Einstein condensation in their system.

  4. Buckle Up

    A combination of shallow dike intrusions and earthquakes causes the surface of active Mauna Loa volcano on Hawaii to flex, but it has not been known how the magma beneath the volcano pools and circulates. Amelung et al. (p. 1026) have mapped the topography of Mauna Loa from 2002 to 2005 using interferometric synthetic aperture radar observations. A new dike-like magma body is swelling in the belly of the volcano in the southwest rift zone. The magma accumulation occurs in a region that was unclamped by previous activity, dike intrusions and earthquakes, which suggests that local stress transfer plays an important role in subsurface magma build up.

  5. Mental Block

    Young children realize that unsupported objects fall to the ground long before they are taught about gravitational attraction. Intuitions such as these can then hamper the learning of scientific facts, such that the world is round, and not flat. Bloom and Weisberg (p. 996) review the notion that beliefs that become established early in life, especially about topics where detailed understanding is practically impossible to achieve directly, contribute to an adult proclivity that renders much of modern science counter-intuitive and hence less readily accepted.

  6. Morality and Emotion

    Although morality is partly a game of self-promotion, people usually do sincerely want peace, decency, and cooperation to prevail within the groups they operate. Haidt (p. 998) reviews how these motives are implemented in large part by a variety of emotionally governed intuitions that arise quickly and automatically, and which then guide controlled processes such as moral reasoning. Much of the information that we are exposed to is perceived and processed without our being fully aware of it, and this situation may be particularly true for emotions. Niedenthal (p. 1002) reviews the connection between perceived, retrieved, and even experimentally induced emotions and how we process emotional information.

  7. From Leaf to Flower

    As spring begins, many plants turn to flower under the control of florigen. The molecular nature of florigen has long been unknown, but the signal was known to originate in leaves, and thus had to travel through the plant to the growing buds. Now Corbesier et al. (p. 1030, published online 19 April) and Tamaki et al. (p. 1033, published online 19 April) show that it is a protein rather than its coding RNA that is the likely florigen signal that moves within the plant (see the 20 April news story by Pennisi). The florigen RNA and protein are encoded by the FLOWERING LOCUS T gene in Arabidopsis and the Hd3a gene in rice.

  8. Smart Drugs, Smarter Tumors

    A promising class of “smart” cancer drugs work by inhibiting specific tyrosine kinases linked to uncontrolled growth. Gefitinib and erlotinib, drugs that target the kinase activity of the epidermal growth factor receptor (EGFR), can be very effective when initially administered to lung cancer patients whose tumors contain activating mutations in the EGFR gene. Almost inevitably, however, these tumors develop resistance to the drugs and begin to regrow. Engelman et al. (p. 1039, published online 26 April) find that drug resistance in a subset of these tumors is caused by amplification of the MET oncogene, an event that in turn activates, via a different route, the same cellular signaling pathway originally activated by the mutant EGFR.

  9. Tumor Suppressor Joined to WNT Network

    Elucidation of the cellular signaling pathways that contribute to cancer development often begins with the identification of a gene mutated in human tumors. Complementary biochemical approaches become especially important when the sequence of the newly identified gene provides few clues as to its function. Major et al. (p. 1043; see the Perspective by Nusse) used analysis of protein interaction networks to define the function of WTX, a tumor suppressor gene found very recently to be mutated in an inherited kidney cancer called Wilms tumor. The WTX protein forms a complex with several proteins in the WNT signaling cascade, including β-catenin, AXIN1, β-TrCP2 (β-transducin repeat-containing protein 2), and APC (adenomatous polyposis coli) and antagonizes WNT signaling by promoting β-catenin degradation.

  10. Seeing the Light


    For organisms to adapt to environmental changes, external signals must affect protein function. Proteins in the PAS (Per-Arnt-Sim) superfamily are involved in transducing diverse external signals, but it has been a challenge to define the signaling pathways. Zoltowski et al. (p. 1054) have determined crystal structures for the dark- and light-activated states of a fungal photoreceptor. Light-induced chemical changes at the active center propagate to large-scale conformational changes at the protein N-terminus that are essential for cellular function.

  11. Making Centrioles

    Centrioles play a key role in the organization of the microtubule cytoskeleton in animal cells, particularly during mitosis when they are responsible for generating the mitotic spindle poles. Rodrigues-Martins et al. (p. 1046, published online 26 April) now show that overexpression of the SAK/PLK4 kinase in the Drosophila germ line drives a dramatic amplification of centrioles in syncytial embryos producing thousands of centrioles. Centrioles are eliminated from eggs during oogenesis, and so the centriole is normally provided by the sperm upon fertilization. However, centriole amplification was observed in unfertilized eggs that are devoid of centrioles, indicating that centrioles can be generated de novo. Thus, centriole formation may represent a self-assembly process in which a preexisting centriole can act as a catalyst and platform for centriole assembly, and in which feedback mechanisms regulate centriole number.

  12. Equal-Opportunity Polymer Crystallization

    Melted polymer chains are stretched during flow, and those that are greater than a critical length undergo a transition from a coiled state to an almost fully extended one. When these flow-extended materials cool and crystallize, they form a “shish-kebab” morphology where primary crystallization occurs in the shish, followed by secondary crystallization in which the kebabs form off the shish backbone. It has long been thought that these extended chains segregated and clumped together to form the shish. However, using fractions of either short, medium, or long chains that were deuterated, Kimata et al. (p. 1014) show that the proportion of long chains in the shish is similar to that in the original melt. They suggest that the extended long chains act as catalysts for crystallization, but once the process begins, they drag in chains of all lengths during the initial stages of crystallization.

  13. Trends in Teamwork

    Currently, many scientists find themselves involved in team-based projects in their research, patenting, or writing. However, little is known regarding the effects or the extent of team participation. Wuchty et al. (p. 1036, published online 12 April) used data on 20 million scientific papers (appearing between 1955 and 2000) and 2 million patents (from 1975 to 1999) to investigate how the production of scientific knowledge and patents has changed in regard to teamwork. The size of research teams is growing and single-authored papers or patents are becoming rarer, both in the sciences and engineering, the social sciences, and patenting, as well as in areas that have traditionally been considered to be the domain of individuals, such as mathematics. The same trend is also becoming apparent in the arts and humanities. On average, teams produced more highly cited papers and patents, and this difference is increasing annually.

  14. The Yin and Yang of Histone Modification

    DNA in eukaryotes is packaged onto nucleosomes, which consist of histone proteins. Covalent modification of histones plays a critical regulatory role in controlling transcription, replication, and repair. Different histone modifications are recognized by different protein modules, and these modules can be found in regulatory complexes with different, even antagonistic functions. Li et al. (p. 1050) tackle this apparent contradiction through analysis of the chromodomain protein Eaf3, which preferentially binds to histone H3 dimethylated at lysine 36. Eaf3 is a subunit of both the Rpd3S deacetylase complex and the NuA4 acetyltransferase complex. The affinity of the Rpd3S complex for nucleosomes and its control of global acetylation levels at transcribed chromatin are determined by the combined activities of Eaf3 and another protein, Rco1, which is not found in NuA4.