Editors' Choice

Science  18 Jun 2010:
Vol. 328, Issue 5985, pp. 1455
  1. Genetics

    Better Breeding

    1. Beverly A. Purnell
    CREDIT: E. R. S. ROLDAN

    Projects aimed at saving endangered species sometimes must rely on a depleted gene pool. Inbreeding is often associated with deleterious effects on reproduction and survival due in part to the expression of recessive alleles, but other mechanisms may also operate. Ruiz-López et al. have examined the effect of inbreeding on sperm integrity for three endangered North African gazelles—Gazella cuvieri, G. dama mhorr, and G. dorcas. DNA fragmentation in sperm was greatly elevated in captive populations of the former two species, which are highly inbred, and DNA damage increased with age. In addition, there was evidence of abnormal sperm structure as well as decreased sperm motility. In a related study, the same authors examined offspring survival rates in G. cuvieri and found that an increase in sperm DNA fragmentation had a large impact on the mortality rate of progeny. Furthermore, when primiparous females mated with males who displayed high levels of sperm DNA fragmentation, the offspring suffered high mortality. Multiparous mothers, however, seemed able to produce viable offspring, possibly because their oocytes could better repair the damaged DNA. Understanding the limitations of inbreeding may assist in designing reproductive programs for endangered species.

    Biol. Reprod. 81, 10.1095/biolreprod.110.084798 (2010); Proc. R. Soc. London Ser. B 277, 10.1098/rspb.2010.0333 (2010).

  2. Biomedicine

    Tuberous Twosome

    1. Helen Pickersgill

    Genetic mutations can lead to the uncontrolled growth of cells; many of these mutations either activate oncogenes or inactivate tumor suppressor genes. However, it has become apparent that inhibiting mutated proteins via small-molecule drugs is nontrivial, and rescuing inactivated tumor suppressors, such as retinoblastoma (Rb), is equally challenging. To tackle these problems, cancer biologists have turned to synthetic lethality, which refers to the interaction between two genes when disrupting the activity of both together causes a cell to die, whereas inactivation of either gene alone has no significant effect.

    Li et al. have used a genetic screen in Drosophila to identify genes that interact in a synthetic lethal manner with Rb. They identified the homolog of tuberous sclerosis complex 2 (TSC2), whose inactivation, along with that of Rb, induced cell death both in Drosophila and in human cancer cells growing in culture and in mouse xenografts. Lethality was due in part to an increase in oxidative stress. The capacity to identify genes that are deadly only within the context of a cancer cell could yield targeted therapeutics that would leave normal cells largely unaffected and thereby reduce the toxic side effects characteristic of many chemotherapeutic agents in use in the clinic.

    Cancer Cell 17, 469 (2010).

  3. Materials Science

    Directing Fibers

    1. Phil Szuromi

    In electrospinning, droplets of liquid polymer solution are charged to a high voltage relative to a metal collector plate. The strong field creates a jet that solidifies to a nanofiber as solvent evaporates. However, the final product is typically a random mat of fibers because of instabilities in the jet motion. Kim et al. show that the collection of electrospun fibers on a sharp tip can control the deposition. Like long cylinders of clay coiling to form a pot, the nanofibers coil onto the electrode tip to form a hollow cylinder about 3 µm wide and 40 µm tall in about 1 s. Badrossamay et al. abandon the use of electrical fields altogether and use a rotating nozzle, which combines pressure and centrifugal forces to create a jet. Aligned fibers of a biodegradable polymer thus prepared were used as a scaffold for rat cardiomyocytes, which developed into beating multicellular tissue.

    Nano Lett. 10, 10.1021/nl100824d; 10.1021/nl101355x (2010).

  4. Ocean Science

    Ross Revisited

    1. Nicholas S. Wigginton
    CREDIT: WOODWORTH ET AL., J. GEOPHYS. RES. 115 (2010)

    Nowadays, satellite altimetry is the preferred means of monitoring sea level with high precision. Correlating modern records with historical measurements, in order to construct a record of long-term sea-level change, therefore depends on the reliability of pre-satellite data. In this context, Woodworth et al. reexamined tidal gauge measurements collected in 1842 in the Falkland Islands by the British explorer James Clark Ross. Based on his diligently kept records and adjustments for air pressure variations and glacial isostatic rebound, the authors estimate the long-term rate of sea-level change between 1842 and the mid-1980s to be +0.75 ± 0.35 mm per year. New measurements based on the same benchmark Ross installed at Port Louis, as well as additional measurements taken with permanent pressure-based tide gauges at nearby Port Stanley over the past 25 years, suggest that the rate of sea-level rise increased to +2.5 ± 0.58 mm per year since 1992. This accelerated rate of sea-level rise agrees with similar trends observed by satellite data in other ocean basins around the world. The data of Ross and his colleagues also provide historical value in reflecting how sampling took place—an especially important contribution because many of Ross' notes—including his original journal documenting his methods—have been missing for over 20 years.

    J. Geophys. Res. 115, 10.1029/2010JC006113 (2010).

  5. Cell Biology

    Making a Move

    1. Stella M. Hurtley
    CREDIT: BRIAN STRAMER

    Hemocytes—macrophage- like cells found in insects—migrate from their birthplace in the head to distribute themselves throughout the whole organism. Stramer et al. examined this migration using high-resolution in vivo imaging of hemocytes expressing fluorescently tagged actin and tubulin. Dynamic rearrangements of the actin (green) and microtubule (red) cytoskeleton were observed as the cells migrated through the Drosophila embryo. In particular, during periods of persistent migration toward a wound, microtubules would form a bundle pointing toward the cell's destination within the forward-moving lamellae of the cell. Proteins known to play a role in directed migration in other systems were also required for hemocyte migration in vivo. If two migrating hemocytes met, after a brief pause during which the microtubule bundles appeared to align, the cells would repel each other, disassembling their microtubule bundles and then reassembling them to move away. This process of contact repulsion presumably helps to generate an even distribution of hemocytes.

    J. Cell Biol. 189, 681 (2010).

  6. Physics

    Keeping Light Around

    1. Jelena Stajic

    Bose-Einstein condensation (BEC) is a phenomenon in which an equilibrium population of bosons (particles of integer spin) slump down to their lowest energy state under conditions of low temperature and high density. The bosons that undergo this transition include cold gases of 87Rb, superconducting electron pairs, and interacting He atoms in their superfluid phase. However, the most ubiquitous bosons, photons, are predicted not to exhibit BEC because their number is usually not conserved and their chemical potential, consequently, vanishes at all temperatures. Klaers et al. now realize a two-dimensional thermalized gas of photons confined in a parabolic potential, with a conserved particle number and a quadratic dispersion—a system equivalent to a gas of massive atoms and expected to undergo BEC under favorable conditions. They achieve this scenario by trapping photons in a curved-mirror optical microcavity filled with dye molecules. The photons are absorbed and emitted repeatedly by the dye molecules, which are pumped by a laser; the pumping ensures that the number of excited dye molecules is constant, in turn ensuring that the photon number is conserved too. The thermalization of the photon gas at the dye solution temperature is confirmed through comparison of measured spectra with theoretical predictions.

    Nat. Phys. 6, 10.1038/nphys1680 (2010).

  7. Psychology

    The Side-Effect Effect

    1. Gilbert Chin

    A robust phenomenon established empirically during the past decade is the tendency of observers to regard morally bad consequences (such as harm to the environment) that occur as a secondary effect of actions taken by an agent (such as a corporate CEO) in the course of achieving the primary effect—an increase in revenue—as having been committed intentionally. In contrast, morally good consequences in a similar scenario are judged as being incidental. A number of explanations for this asymmetry (also known as the Knobe effect) have been put forth; most prominent, perhaps, is the proposal that the moral valence of the side effect alters the observer's inference about the agent's mental state; that is, whether the CEO acted with intent. Uttich and Lombrozo bring to bear a series of vignettes in which the type of social norm (moral versus conventional), the kind of behavior (norm-conforming versus norm-violating), and the outcome valence (helpful versus harmful) were varied independently. Their results support a “rational scientist” framework, so that the observer's computation of the agent's state of mind weights actions that flout commonly accepted rules of behavior as being more informative and hence diagnostic of intentionality than conformist ones.

    Cognition 116, 87 (2010).

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