This Week in Science

Science  21 Mar 2008:
Vol. 319, Issue 5870, pp. 1585
  1. Secrets of an Ancient Thigh Bone

    CREDIT: RICHMOND AND JUNGERS.

    The functional and phylogenetic significance the 6-million-year-old femora of Orrorin tugenensis, one of the earliest fossils from the human lineage has been debated since their discovery in Kenya in 2000. Richmond and Jungers (p. 1662; see the news story by Gibbons) present a comparative morphometric analysis of these remains with femora from modern humans, living apes, and other fossil hominins to reveal and confirm bipedal adaptations in the femora of Orrorin. The Orrorin femora closely resemble those of Australopithecus and Paranthropus, which are 2 to 3 million years old, which contradict the hypothesis that Orrorin is more closely related to Homo than to Australopithecus. The morphology of the Orrorin femora strongly suggests that the australopithecine pattern of hip biomechanics evolved very early in human evolution and persisted as a stable locomotor strategy for as long as 4 million years, the majority of human evolutionary history.

  2. Small Minerals, Big Implications

    Many geologic processes involve reactions between minerals and between minerals and surface water, groundwater, or air. Increasingly, it has been recognized that many important reactions involve minerals that are less than about 1 micrometer in size (or nanominerals), and two Reviews discuss how minerals properties can depend on crystal size. Hochella et al. (p. 1631) summarizes our understanding of these nanominerals, their occurrence, and their potential implications in geologic processes. Navrotsky et al. (p. 1635) focus on the thermodynamics and stability of one of the most important and ubiquitous classes of nanominerals, the iron oxides.

  3. Diffusion in Overdrive

    The motion of impurity atoms within a crystal is a thermally driven process, and for a perfect crystal, this process should be fairly slow. However, there are numerous examples where faster diffusion has been observed that generally have been attributed to the presence of dislocations and grain boundaries. Legros et al. (p. 1646) measure the motion of silicon precipitates inside a thin film of aluminum and directly observed “pipe diffusion,” in which the dislocations in the aluminum act as a channel for more rapid travel of the silicon. Diffusion can be accelerated by three orders of magnitude compared with bulk diffusion, in support of the theories on pipe diffusion.

  4. How Titan Turns

    Titan, Saturn's largest moon, is covered with an icy crust and dense atmosphere. Lorenz et al. (p. 1649; see the Perspective Sotin and Tobie) used several years of Cassini radar observations to show that Titan's rotational period differs from its orbital period, which implies that there is an exchange of angular momentum seasonally between the planet and its atmosphere. Modeling of this exchange requires an internal model of Titan that includes a crust and core separated by a liquid ocean, as on Jupiter's moon Europa.

  5. Ancient Volcanic Gas in Glass

    The influence on climate of massive volcanic eruptions that have formed flood basalts, such as the Deccan traps at the end of the Cretaceous, has been difficult to assess, in part because of the lack of data on the gas contents of most of the magmas (much of the erupted basalt degassed as crystals formed or during later alteration). Self et al. (p. 1654; see the Perspective by Scaillet) screened many samples of the Deccan basalts and found a few samples preserving glass inclusions in crystals or glassy rims that could preserve information on the original sulfur and chlorine contents of the Deccan magma. The results imply that the Deccan basalts released huge amounts of sulfur, perhaps nearly an order of magnitude or more than recent global anthropogenic emissions, for decades or centuries.

  6. Low-Field Multiferroics

    CREDIT: ISHIWATA ET AL.

    The ability to electrically manipulate the magnetic properties of a solid offers great potential for device functionality. Materials of particular interest are those in which the magneto-electric (ME) response, which couples electric and magnetic dipole moments, is an intrinsic property of the crystalline symmetry. So far, however, the ME effect in such materials has only been seen at large magnetic fields and low temperature. Ishiwata et al. (p. 1643) present results on the hexaferrite Ba2Mg2Fe12O22, which has a chiral spin structure, and show that the electric polarization can be manipulated with a very low magnetic field of 30 millitesla.

  7. Insights into Early Multicellular Life

    Multicellular life first appeared in the Late Precambrian, but the affinity and habits of many of the fossils remain enigmatic. Droser and Gehling (p. 1660; see the Book Review by Xiao) reveal a newly described tubular organism that is particularly abundant in one area where many fossils have been found, the Ediacara of the Flinders Range of South Australia. The tubular fossils are as long as 30 centimeters and 12 millimeters in diameter and are composed of smaller units. A few exhibit branching, and multiple modes of growth are represented. The fossils reveal attachment structures to the sediment substrate, and probably represent a stem-group Cnidarian or Poriferan.

  8. Functional Differentiation Within the Human Hippocampus

    CREDIT: BAKKER ET AL.

    Structures in the temporal lobe of the human brain support declarative (fact and event) memory. How these structures operate and interact is unclear. Recent studies in rodents observed pattern separation processes in the CA3 field and dentate gyrus. Using high-resolution brain imaging, Bakker et al. (p. 1640; see the Perspective by Leutgeb) have now analyzed these operations in humans. A technique was developed to infer changes in the pattern of activity across neurons in the medial temporal lobe with respect to pattern separation and pattern completion processes. In striking similarity to the rodent data, strong pattern separation was observed in the CA3 and dentate gyrus, whereas a tendency toward pattern completion was observed in hippocampal CA1, the subiculum, the entorhinal, and parahippocampal cortices.

  9. Radical Avoidance Strategy

    Staphylococcus aureus is responsible for severe infections that, in the wake of widespread antibiotic resistance, are a growing threat. Unlike very closely related commensal species, S. aureus can both inhibit and avoid the damaging effects of NO released during host defensive responses. Richardson et al. (p. 1672, see the cover) show that in addition to free-radical scavenging mechanisms, S. aureus possesses an inducible L-lactate dehydrogenase through which it can divert glucose metabolism exclusively to L-lactate during NO exposure when other more sensitive enzymes shut down. This strategy allows the organism to maintain redox balance, retain virulence, grow, and replicate despite the host assault.

  10. Faulty Scaffolding and Cancer

    Differentiation, survival, and growth of B cells requires proper functioning of the nuclear factor-κ B (NF-κB) signaling pathway, including CARD11, a cytoplasmic scaffolding protein that serves as a docking site for signaling molecules. Lenz et al. (p. 1676, published online 6 March) have discovered that a certain subtype of diffuse large B cell lymphoma, the most common form of non-Hodgkin's lymphoma in humans, is caused by mutations in the CARD11 gene. In cell culture experiments, these mutant forms of CARD11 caused inappropriate activation of the NF-κB pathway.

  11. Individual Egg, Individual Attention

    Female flies are selective in choosing suitable sites to lay their eggs, presumably to promote survival of their progeny. However, Yang et al. (p. 1679) found that even at sites suitable for egg-laying, for every single egg to be deposited, Drosophila melanogaster went through a stereotyped behavior sequence: A searchlike program, egg-laying, cleaning of ovipositor, and rest. Females selected plain or bitter-tasting substrates over sucrose-containing media when given a chance to explore available options. However, when only sucrose was available, they laid eggs on it, and in approximately equal numbers, which suggests that while sucrose is not their preferred choice, it is not absolutely repulsive.

  12. 'Tis Better to Give

    Now that the holiday shopping season is over, many people can ask whether, as in the adage, it truly was better to give than to receive. Dunn et al. (p. 1687) address this question, by using the results from a survey of Americans, by analyzing the actual spending patterns of bonuses meted out at a Boston area firm and by conducting an experimental manipulation on a stereotypical subject pool (psychology undergraduates). All three studies suggest that spending money on other people produces more happiness than spending on oneself, in contrast to the expectations of the undergraduates.

  13. Martian Chlorides

    Chloride minerals commonly form from the evaporation of standing bodies of water or groundwater, or through volcanic outgassing. These processes likely operated early in Mars' history, but the absence of recognizable deposits has been problematic. Osterloo et al. (p. 1651) now report the apparent detection of chloride deposits, via spectrometers on Mars Odyssey, in several small but perhaps widespread deposits in the Southern Highlands region, which represent some of the older rocks on Mars. The specific minerals are uncertain, but their distribution, visible appearance, and are broadly consistent with formation by evaporation.

  14. Second-Sourcing OH Radicals

    Hydroxyl radicals (OH) are the most important oxidant in the atmosphere, despite their low concentration. It has been thought that the major route of production of hydroxyl radicals is the photolysis of ozone, although there are some conditions, such as at the poles where the solar zenith value is very high, where there is a significant discrepancy between measured and calculated OH concentrations. Li et al. (p. 1657; see the Perspective by Wennberg and Dabdub) show that the reaction of electronically excited NO with water is an important source of tropospheric OH radicals and can supply as much as 50% of the OH under certain conditions. This chemistry also could have important implications for understanding OH abundances in places with high concentrations of atmospheric NOx, such as large cities.

  15. Paradoxical Signaling

    In contrast to its role in stimulating DNA synthesis and cell division, the cyclin-dependent kinase CDK1 has been implicated in signaling that leads to cell death in nonproliferating neuronal cells. Yuan et al. (p. 1665) present evidence that the CDK1 protein kinase phosphorylates the FOXO1 transcription factor, which leads to the accumulation of FOXO1 in the nucleus and activation of a FOXO1-dependent reporter gene. This conclusion contrasts with previous work which reported that phosphorylation of FOXO1 by CDK2 caused movement of FOXO1 out of the nucleus and decreased FOXO1-dependent transcription. In proliferating cells, CDK1-induced activation of FOXO1 led to increased expression of the gene encoding another kinase that contributes to regulation of mitosis—polo-like kinase (Plk). These results may lead to better understanding of neuronal degeneration.

  16. ALS Culprit

    Amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease) is a fatal adult-onset motor neuron disorder that is inherited in an autosomal dominant fashion in 5 to 10% of cases. The cause of 95% of ALS cases is uncertain. The TAR DNA binding protein (TDP-43) is a major component of the ubiquitinated inclusions that are the pathological hallmark of ALS. TDP-43 is a predominantly nuclear protein involved in the regulation of messenger RNA transcription and splicing. Sreedharan et al. (p. 1668, published online 28 February) now describe a missense mutation in exon 6 of TARDBP in a large British ALS kindred. The mutation lies within the highly conserved C-terminal domain region of TDP-43, which mediates protein-protein binding and interaction with components of the spliceosome. In transfected mammalian cell lines, the mutant protein showed increased fragmentation and, when expressed in embryonic chicken spinal cord, caused apoptotic neural cell death and embryonic developmental arrest. This pathophysiological link between TDP-43 and ALS may clarify the pathogenesis of a condition that is predominantly sporadic.

  17. BDNF + Protein Synthesis = Synaptic Plasticity

    Protein synthesis is required for consolidation of memory and has been used to characterize memory systems. However, it is not clear whether protein synthesis can regulate synaptic plasticity at the level of single synapses and how protein synthesis affects synaptic structures, such as dendritic spines. Tanaka et al. (p. 1683, published online 28 February; see the Perspective by Korte) discovered that repetitive synaptic stimulation in synchrony with postsynaptic spike induces rapid and long-term spine enlargement, which occurs at the level of single spines, and is associated with increases in glutamate sensitivity. This associative paradigm specifically produces long-term and protein synthesis-dependent changes. Brain derived neurotrophic factor (BDNF) mimics the effects of postsynaptic spiking and occludes the effects of associative stimulation. Thus, protein synthesis and BDNF are required for the alterations in spine morphology associated with synaptic plasticity.