This Week in Science

Science  02 Jul 2004:
Vol. 305, Issue 5680, pp. 13
  1. Finding African Ancestors

    CREDIT: KENYA NATIONAL MUSEUM, NAIROBI

    Across Europe and Asia, fossil evidence for hominids that dates from 1.0 to 0.5 million years ago can be associated with distinctive tools, notably handaxes. Hominid fossils from this time period in Africa, however, are notably scarce, despite an abundance of tools and other animal fossils. This difference has limited regional comparisons during this critical time period. Potts et al. (p. 75; see the Perspective by Schwartz) now describe a fossil hominid cranium found in Kenya, from apparently a small individual, that dates to about 930,000 years ago. The fossil is from near one of the richest Acheulean handaxe sites in Africa. Its features, while similar in many respects to Homo erectus, implies a wide variation in hominids at this time.

  2. Space Weather from All Perspectives

    Coronal mass ejections (CMEs) are highly energetic eruptions of magnetized gas from the solar corona that are often associated with solar flares or filaments. These bubble-like bodies are propelled into the heliosphere and produce fluctuations in Earth's magnetic field and ionosphere density. These fluctuations can damage satellites, disrupt radio communications, damage electrical power grids, and expose humans in spacecraft or airplanes at high altitudes to high doses of radiation. Moran and Davila (p. 66, published online 27 May 2004; see the Perspective by Raymond) have determined the velocity and three-dimensional shape of several CMEs through analysis of SOHO data. These results will help solar physicists better understand how these energetic ejections form and allow others to better prepare for the inevitable space weather at Earth.

  3. Lipids Throw a Curve

    During mating of the protozoan Tetrahymena, hundreds of fusion pores form between the two cell membranes in a region about 10 micrometers across. Conjugation has been shown to depend on the synthesis of new lipids. Ostrowski et al. (p. 71) imaged these mating tubes with time-of-flight secondary-ion mass spectrometry and found that the distribution of lipids in the Tetrahymena mating tube is heterogeneous. The fusion region is enriched with 2-aminoethylphosphonolipid, a high-curvature lipid. These results suggest that fusion may be driven by the redistribution of lipids that form surfaces with different degrees of curvature.

  4. Secretory Lysosomes in Health and Disease

    CREDIT: STINCHCOMBE ET AL.

    Waste materials in cells are transported to the lysosome for destruction, but lysosomes have roles to play in cells beyond being dustbins. Stinchcombe et al. (p. 55) review the role of a specialized class of lysosomes important in a variety of cell types that defy definition as a final resting place for defunct material. In certain cell types, especially in cells of the immune systems, lysosomes can do double-duty as secretory organelles. Several genetic disorders of the immune system involve defects in the functions of secretory lysosomes. Similarities in the membrane-trafficking pathways involved in secretory lysosomes and melanocytes means that, in some rare genetic disorders, immune dysfunction and albinism are linked.

  5. Optical Fibers with a Twist

    One way to boost transmission rates over optical fibers is to manipulate different polarization and wavelengths within the fiber and allow that information to be read by coupling it out of the fiber. Kopp et al. (p. 74) present a simple technique in which chirality is introduced into optical fibers via periodic twists. Depending on the periodicity of the twist, they can couple light of particular wavelength out of the fiber and also select the polarization state of transmitted light.

  6. Dissecting Cytokinesis

    During cell division, the process of physically separating daughter cells is known as cytokinesis. Skop et al. (p. 61, published online 27 May 2004; see the cover) identified components important for cytokinesis by combining a proteomic analysis of the midbody, an organellar remnant of cytokinesis in mammalian cells, followed by functional screening of homologous genes in Caenorhabditis elegans. Common components were involved in diverse dynamic membrane events in the cytokinetic furrow, the germ line, and neurons.

  7. Reassessing Ancient Martian Climate

    Dendritic valleys on the plateaus and canyons of Valles Marineris on Mars are attributed to periods of rainy weather about 2.9 to 3.4 billion years ago. Based on these fluvial landforms, Mangold et al. (p. 78; see the news story by Kerr) suggest that the rainy periods were sustained for long periods of time and required warmer temperatures in the Late Hesperian epoch, when Mars had been thought to be cold.

  8. Ultimate Memory Storage Sites

    The formation of declarative memories involves changes in synaptic plasticity within structures of the medial temporal lobe, including the hippocampus. However, the hippocampus has a time-limited role in long-term memory storage—other structures eventually become capable of independently supporting the retrieval of remote memories. Maviel et al. (p. 96) combined brain imaging of activity-dependent genes with region-specific neuronal inactivation in mice submitted to either recent or remote memory testing. Specific neocortical association areas (prefrontal, anterior cingulate, parietal, and retrosplenial) mediated long-term spatial memory formation with distinct functional neuronal mechanisms underlying neocortical reorganization during memory consolidation. Inactivation of each of the identified areas led to impairment of remote memory retrieval, whereas recent memory retrieval was spared.

  9. Protein Microarrays Made Simple

    Protein arrays are a valuable tool in investigating protein function, but producing the arrays has represented a difficult technical challenge and has limited their application. Now Ramachandran et al. (p. 86) describe an approach that may make protein chips more practical. They printed complementary DNAs encoding epitope-tagged target proteins onto glass slides. The proteins were expressed in a cell-free system and immobilized in situ through their epitope tags. The interactions between 29 DNA replication initiation proteins were analyzed with this technique.

  10. Understanding the Beginnings of Reproductive Isolation

    Hybrid male sterility is often the first mechanism of isolation to appear in the process of speciation. Sun et al. (p. 81) examine the evolution, expression patterns, and wild-type function of the Drosophila “speciation” gene Odysseus (Ods) that causes hybrid male sterility. They show that Ods is misexpressed in hybrids, and identify the normal role of Ods in enhancement of spermatogenesis in young male flies. Spermatogenesis may be more sensitive than other developmental processes to disturbances in gene expression and, if so, any of the genes involved in sperm production be implicated in hybrid sterility.

  11. Diverse Development Without Fusion

    CREDIT: HARRIS ET AL.

    Cells derived from the bone marrow have lately been showing a surprising propensity to contribute to unexpected tissues. Considerable debate centers around whether the results stem from aberrant cell fusion or to other mechanisms. Harris et al. (p. 90; see the news story by Vogel) now use the cre/lox recombination system to identify donor cells that have integrated into tissues without having fused with existing recipient cells. In these mice, unfused cells from male donor bone marrow were found in the lung, liver, and skin.

  12. Membrane Fission and Golgi Division

    During cell division, single-copy organelles like the Golgi complex must be partitioned faithfully to each daughter cell. Hidalgo Carcedo et al. (p. 93; see the Perspective by Diao and Lowe) now describe a protein termed BARS that plays a role in Golgi partitioning by severing Golgi tubules. In vitro, BARS can promote the fission of isolated Golgi membranes. Activity of the BARS protein is also important in allowing intact cells to enter mitosis.

  13. Context Is King

    Developing axon encounter an array of signals telling them to go this way or that. In some cases, the same signaling molecule in one context says “this way” and in another context says “that.” Chang et al. (p. 103) have now elucidated some of the molecular complexity in these seemingly redundant but contradictory instructions. Identification of a receptor protein tyrosine phosphatase, CLR-1, in Caenorhabditis elegans provides the key. In some contexts, the CLR-1 partnership with netrin, an axon-guidance molecule, results in attraction, and in other contexts, results in repulsion of growing axon tips.

  14. Evolution in a Digital World

    The factors underlying patterns of species richness observed in nature remain a principal focus of ecology. What causes the patterns in species richness along gradients of productivity, and what evolutionary processes might be involved in generating the observed patterns? Chow et al. (p. 84) applied in silico evolution of digital organisms to the emergence and maintenance of functionally distinct species in a homogeneous environment, as a function of productivity. Adaptive radiation that led to a peak of species richness occurred at intermediate levels of resource flow, a pattern similar to that observed in natural ecosystems.

  15. The Ups and Downs of Neural Activity

    Neurons function through changes in membrane potential that are induced by transient openings and closings of ion-selective channels (gated either by voltage or by neurotransmitters). The various ions, primarily K+, Na+, and Ca2+, move passively, down their electrochemical gradients, and transporting these ions back whence they came requires energy. Kasischke et al. (p. 99; see the Perspective by Pellerin and Magistretti) use two-photon imaging of a reduced form of nicotinamide adenine dinucleotide (NADH) to examine the spatial and temporal events during neuronal activity. An initial consumption of NADH in dendrites caused by oxidative metabolism in mitochondria is followed by glycolytic (nonoxidative) metabolism in astrocytes; this latter process generates lactate, which is shuttled out of the astrocyte and into the neuron, where it can then be “burned” within the mitochondria.

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