This Week in Science

Science  25 Nov 2011:
Vol. 334, Issue 6059, pp. 1029
  1. Animal Life on Earth


    The fossil record reveals that animals diversified greatly about 540 million years ago during the beginning of the Cambrian, but the deeper origins of this event have remained enigmatic since Darwin's time. Based on recent fossil finds and improved dating, Erwin et al. (p. 1091) present a molecular estimate of relations and origination times of early animals. The major animal clades appear to have diverged tens of millions of years before the Cambrian, and the last common animal ancestor may have lived about 800 million years ago. Diversification probably involved new forms of gene regulation when environmental changes at the beginning of the Cambrian allowed the emergence of new ecosystems.

  2. Endoplasmic Reticulum in the Spotlight

    The endoplasmic reticulum (ER) is the entry portal for newly synthesized membrane and secretory proteins and, as such, represents a key lynchpin in the way a cell communicates with the outside world (see the cover). Smith et al. (p. 1086) review how the cell monitors the folding of proteins within the ER and disposes of those that are misfolded, in a tightly regulated process termed ER-associated degradation (ERAD). However, sometimes ERAD is not enough and, in order to deal with misfolded proteins in the ER, the cell needs to enlist additional players. Walter and Ron (p. 1081) review the unfolded protein response (UPR) pathway that is stimulated when normal ER qualitycontrol pathways like ERAD are overwhelmed, and unfolded or misfolded proteins begin to accumulate within the ER.

  3. Alternative Amination

    Amines are generally known for their reactivity at the nitrogen center. McNally et al. (p. 1114) have discovered a more unusual mode of reactivity whereby alkyl (C-H) groups, adjacent to the nitrogen, bond to aryl rings by effective displacement of a cyano leaving group. This coupling of alkyl amines with cyanoarenes was uncovered in the course of a protocol screening the potential reactivity of a wide range of unusual reagent combinations.

  4. Galactic Superbubble

    Cosmic rays are energetic subatomic particles that bombard Earth from space. They are generally thought to be accelerated in the shocks driven by the explosion of massive stars. An alternative scenario involves acceleration within superbubbles—regions of space filled with hot and tenuous gas, which are carved around stellar associations by strong stellar winds originating from massive stars and multiple stellar explosions. Ackermann et al. (p. 1103; see the Perspective by Binns) present gamma-ray images obtained with the Fermi Large Area Telescope of a region in our Galaxy, characterized by intense star formation. The gamma-ray emission exceeds galactic gamma-ray background, suggesting the presence of freshly accelerated cosmic rays within a superbubble.

  5. Elementally Polar


    Chemists had long ago distinguished polar molecules like HF from nonpolar molecules like N2: Certain elements attract electrons more forcefully than others, leading to asymmetric behavior in an electric field when they are bound to one another. Li et al. (p. 1110) studied a recently discovered metastable partnership between a rubidium (Rb) atom in its ground state and another Rb atom with its valence electron-excited to a high-energy Rydberg state. Somewhat counterintuitively, this molecule manifests intrinsic polarity, even though it is composed of a single element.

  6. Ancient Fisheries

    Early humans exploited coastal marine resources early and often, but—even though they must have conducted open ocean voyages by 50,000 years ago (to get to Australia, for example)—evidence of significant offshore fishing has been sparse. O'Connor et al. (p. 1117) now describe deposits containing bones of a wide variety of deep-sea species and fishing gear from a shelter in East Timor beginning about 42,000 years ago. Overall, fish make up the majority of the animal remains at the shelter, and about half of the fish are pelagic species, such as tuna. Although it is not clear how the fishing was conducted, especially early, some bone fishhooks are found in the younger deposits.

  7. Biased Biodiversity?

    The fossil record provides the basis for reconstructing trends in biodiversity throughout Earth's history. But do the sedimentary rocks that exist today provide a broad enough representation over various geologic time periods, or is there an inherent sampling bias imparted during preservation that overprints biodiversity trends? To address this question, Hannisdal and Peters (p. 1121; see the Perspective by Crampton) looked at how various environmental factors—including sea level, ocean chemistry, and climate—correlated with biodiversity records of marine invertebrates throughout the Phanerozoic (the last 530 million years). It seems that the fossil record has indeed been affected over geologic time by external environmental pressures.

  8. Applying Brainpower to Mouse Obesity

    Neuronal replacement therapy—the idea that donor neurons can repair a brain injured by trauma or neurodegenerative disease—continues to attract considerable interest. Such therapy is fraught with challenges, however, because its success requires that donor neurons differentiate and form synaptic connections with appropriate neurons in the host. Czupryn et al. (p. 1133) transplanted immature neurons from the hypothalamus of wild-type donor mice into the hypothalamus of mutant mice that were morbidly obese because of a genetic deficiency of the receptor for leptin, a metabolic hormone that signals in the hypothalamus. The donor neurons differentiated into four distinct neuronal types that formed functional synapses, resulting in restoration of hypothalamic leptin signaling and partial reversal of obesity and metabolic defects in the recipient mice.

  9. Primed for Death

    Decades after their introduction into the clinic, cytotoxic chemotherapeutic drugs continue to be the mainstay of cancer patient care. Why chemotherapeutic drugs are effective in some tumors and not others is not fully understood. Ni Chonghaile et al. (p. 1129, published online 27 October; see the Perspective by Reed) hypothesized that differences in chemotherapeutic response may be due to pretreatment differences in the readiness of tumor cells to undergo apoptosis (a form of cell death), a measurable property that they call “mitochondrial priming.” Consistent with this idea, patients with highly primed cancers were found to have a superior clinical response to chemotherapy. In vitro manipulations that increased mitochondrial priming in tumor cells enhanced their sensitivity to chemotherapy.

  10. Go with the Flow

    Polarization in Caenorhabditis elegans zygotes is a prime example of coupling between pattern-forming biochemical networks and the mechanical processes for enacting morphologic change. However, despite 20 years of research on the partitioning-defective (PAR) polarity proteins, we still do not understand the underlying mechanistic basis of this mechanochemical coupling or PAR polarization. Through quantitative experiments and modeling, Goehring et al. (p. 1137, published online 20 October) show that passive advection by actively generated fluid flow is sufficient to drive asymmetry of PAR proteins and thereby can act as a trigger for pattern formation.

  11. Getting Rid of Mr. Mitochondrion


    In most multicellular organisms, mitochondria—the so-called powerhouses of the cell—come exclusively from the oocyte. However, how sperm-derived paternal mitochondria disappear selectively from the cytoplasm during embryogenesis is unclear (see the Perspective by Levine and Elazar). Sato and Sato (p. 1141, published online 13 October) and Al Rawi et al. (p. 1144, published online 27 October) found that autophagy in Caenorhabditis elegans is induced by the penetrated sperm immediately after fertilization. Autophagy selectively eliminated the paternal mitochondria in embryos and was required for maternal inheritance of mitochondria. Furthermore, examination of mouse embryos revealed a conserved mechanism among these species.

  12. Riding the Wave

    Humans have spread to occupy most of the world, but the genetic consequences of this demographic expansion are not known. Moreau et al. (p. 1148, published online 3 November) examined the expansion of colonies in Quebec from 1686 to 1960, on the basis of church registries. Individuals on the wave front had significantly higher fitness (reproductive success) than those within the core of the population. Women on the wave front married on average 1 year earlier than those in the core, extending their reproductive potential, and wave front families would have experienced greater availability of land for offspring, relative to those within the core.

  13. The Stressed Brain

    Animal experiments have shown that stressors trigger a neurochemical cascade that leads to the release of stress-related neuromodulators. These modulators change the cognitive state of the brain by altering the connectivity of large-scale neuronal populations. In human test subjects, Hermans et al. (p. 1151) compared a neutral paradigm with the effects of an acute stressor on functional brain activity and simultaneous changes in subjective reports of emotionality and physiological measures of neuroendocrine and autonomic activity. Robust stressor-related changes in functional neuronal activity and connectivity within a so called salience network of brain areas were observed, which correlated with increased reports of negative emotionality by the participants, as well as with increases of cortisol and alpha amylase in their saliva.

  14. Piercing the Viral Armor

    A protective shield of glycans is a strategy that viruses use to escape antibody recognition. However, recently, broadly neutralizing antibodies to HIV have been identified that appear to bind directly to the glycan coat of its envelope protein, gp120. Pejchal et al. (p. 1097, published online 13 October) report the structure of the antigen-binding region of the potent and broadly neutralizing antibody, PGT 128, bound to a glycosylated gp120 outer domain. The antibody penetrates the glycan shield by binding to two highly conserved glycans and to a portion of the protein surface. The contact with two glycan chains explains the antibody's high affinity for a large glycan epitope.

  15. Newly Minted Pulsar

    Globular clusters are compact groups of hundreds of thousands to millions of stars. About 200 are known to orbit our Galaxy; a few are known to emit γ-rays. This emission is thought to originate from the population of millisecond pulsars that inhabits these clusters; however, these pulsars have only been detected at radio wavelengths. Freire et al. (p. 1107, published online 3 November) report the detection of an individual pulsar in a globular cluster at γ-ray wavelengths and show that the cluster's γ-ray emission is dominated by that single pulsar. This pulsar is much more luminous than previously detected millisecond pulsars, suggesting that it is the youngest yet to be detected.

  16. Between a Rock and a Hard Place

    Studies of the influence of climate change on organisms often focus on single effects; for example, the influence of temperature increases on a species range. Harley (p. 1124; see the Perspective by Nogués-Bravo and Rahbek) looked at the influence of increased temperature on the interaction between a predator (the sea star Pisaster ochraceus) and its prey (mussels and other marine invertebrates) in the intertidal zone, across both space and time. As temperature increased, the vertical extent of mussel beds above the high tide line decreased owing to thermal stress. This reduced the amount of predator-free space available and led to range contraction and even local extinction at some sites. When predation pressure was experimentally reduced, prey species were able to occupy extralimital sites and species richness was increased.

  17. Biased Toward Females

    Many species have life histories in which, locally, one or a few mated females contribute broods from which mated daughters disperse. These species are often characterized by extreme female-biased sex ratios, as expected, on the basis of theoretical studies of Local Mate Competition (LMC). Macke et al. (p. 1127, published online 3 November) studied sex ratios in the spider mite Tetranychus urticae, a classical example for sex-ratio adjustment in response to LMC. Starting from the same base population, independent populations were evolved under three intensities of LMC for 2 years and showed sex ratios within each selection line that fit perfectly with theoretical predictions.

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