Editors' Choice

Science  23 Apr 2010:
Vol. 328, Issue 5977, pp. 406
  1. Education

    Contextual Teaching

    1. Brad Wible
    CREDIT: © 2006 BY CONTRA COSTA TIMES

    Can integrated approaches to literacy instruction alleviate the disadvantages and poor performance of students in urban schools, and are there differential effects on students not native to the language of the school system? Lesaux et al. have developed a program to improve a foundational element of reading comprehension—vocabulary. The 18-week intervention involved sixth-grade teachers and 500 of their students, roughly three-quarters of whom were not native English speakers, from urban schools. The program differed from traditional instruction in several ways: (i) Rather than memorizing lists of words and definitions, students read passages from texts describing real-world events; (ii) rather than literature-based texts, students read expository, nonfiction text from a news magazine; (iii) academic words (such as evidence and method) that appear across a range of disciplines were emphasized; and (iv) students didn't just read, but also discussed and wrote passages. Multilevel modeling indicated that this regimen improved students' abilities to understand words in multiple forms (for instance, complex versus complexity) and in multiple contexts. Results on a measure of reading comprehension were promising, and this program was comparably effective for native and non-native English speakers. Two challenges must be met if such research is to contribute at scale: Interventions must be efficacious yet also easily implemented and maintained in mainstream classroom settings. Observation, surveys, and interviews revealed that program materials and training empowered teachers to implement the program with good fidelity.

    Reading Res. Quart. 45, 196 (2010).

  2. Biotechnology

    Positive Reinforcement

    1. Jake Yeston

    It's often easier, when formulating rules, to tell people what not to do. Positively encouraging desirable behavior requires all manner of subtle distinctions that simple prohibitions avert. A similar contrast arises in efforts to direct the behavior of bacteria. Advances in genetic engineering have recently enabled researchers to modulate the internal chemistry of organisms such as Escherichia coli in order to favor excess production of a particular metabolite of commercial interest—a strategy prized for its chemical efficiency and waste minimization relative to synthetic elaboration of petroleum feedstocks. The modulation is straightforward when it entails deleting genes that disrupt the path to the desired product; determining which genes may need a boost is rather more complicated, given the interconnected nature of the cell's network of metabolic reactions. Choi et al. have developed a method of simulating metabolic flux for the express purpose of predicting which genes ought to be amplified in order to optimize production of a particular target compound. They demonstrate the method by optimizing for lycopene production in E. coli. Though not every gene identified in the simulation proved beneficial to amplify in practice, the method showed significant promise, particularly in tandem with a more traditional gene knockout simulation.

    Appl. Environ. Microbiol. 76, 10.1128/AEM.00115-10 (2010).

  3. Astronomy

    Whence the Spirals?

    1. Maria Cruz
    CREDIT: BOB FRANKE

    Observations of the Milky Way and its nearest spiral neighbor, Andromeda, suggest that the outer stellar regions of these galaxies assembled by accretion of smaller, satellite galaxies. How common is this process in shaping such large spiral galaxies? Using the Subaru Telescope in Hawaii, Mouhcine et al. surveyed the outer regions of NGC 891, a spiral galaxy analogous to the Milky Way but located 30 million light-years away and thus well outside our immediate vicinity. The map of stars around this galaxy shows signs of tidal interactions and satellite disruption, including arc-like streams, one of which loops all the way around the galaxy. Together with observational evidence from other galaxies, this result suggests that accretion of small satellites may indeed be a common process in the formation of spiral galaxies. NGC 891 is also surrounded by a thick envelope of stars, which may have resulted from tidal disruption of several small satellite galaxies. This may also be a common property of large spiral galaxies.

    Astrophys. J. 714, L12 (2010).

  4. Plant Science

    Cell Wall Construction

    1. Pamela J. Hines
    CREDIT: JING-KE WENG

    Lignin, a heterogeneous polymer built from p-hydroxycinnamyl monomers, provides the stiffness in woody tissues of vascular plants. The resiliency of lignin may be useful to a tall tree, but it is an obstacle in the extraction of sugars from plant tissues that are used as biofuels. Angiosperms use a larger set of subunits—featuring monomers in which hydroxylation at both meta positions has occurred—to make lignin than do most plants in the lycophyte lineage, which diverged from the angiosperm lineage 400 million years ago. Weng et al. have identified a cytochrome P450 enzyme from the lycophyte Selaginella that bears limited similarity to angiosperm enzymes, and when the Selaginella enzyme was introduced into the angiosperm Arabidopsis, a new form of lignin was detected. These results suggest that the enzymatic diversity of the broader plant kingdom might be informative for taming recalcitrant biosynthetic pathways in potential biofuel crops.

    Plant Cell 22, 10.1105/tpc.109.073528 (2010).

  5. Evolution

    Three Little Unexpected Children

    1. Guy Riddihough

    The genetic code consists of triplets of nucleotides (codons) that are read by complementary triplets (anticodons) in amino acid–carrying tRNAs; for example, the codon CAU is read by an AUG-anticodon in tRNA charged with the amino acid histidine (His). Charting the evolution of the triplets is complicated because almost nothing is known of what came before. The stereochemical hypothesis suggests that codons or anticodons arose through specific recognition of their cognate animo acid. Johnson and Wang looked through the three-dimensional structures of ribosomes from four different species to see if any of the amino acids in the ribosomal proteins might be found in the vicinity of their respective codon or anticodons in the ribosomal RNAs. Although no amino acids were preferentially enriched near their contemporary codons, 11 amino acids were found close to their anticodons. It has been proposed that these 11 amino acids joined the primordial genetic code later on, perhaps during the concurrent evolution of a primitive translation system. Statistical analysis of 4 of the 11 amino acids suggests that they underwent reassignment; His was initially coded by four codons—CAU, CAC, CAA, and CAG—but CAA and CAG were subsequently ceded to the upstart glutamine.

    Proc. Natl. Acad. Sci. U.S.A. 107, 10.1073/pnas.1000704107 (2010).

  6. Education

    All Three R's in Science

    1. Melissa McCartney

    Writing and argumentation skills are critical to the successful scientist, yet they are often overlooked in science curricula. Do such abilities transfer well from classes in more literacy-focused disciplines? Part of a recent study by Adams et al. investigates whether undergraduate students revising scientific texts are able to recognize and address discrepancies in structure and argument or whether they focus mainly on spelling and grammar. The study assessed vocabulary, content knowledge, and verbal memory of 48 students in the first year of a psychology degree program. Students were asked to analyze scientific texts containing errors in three categories: language, structure (i.e., lack of conclusion), and argument (i.e., lack of evidence). The results showed that students were better able to identify errors of language and structure than of argument, and topic knowledge and verbal working memory seemed to be less important than verbal short-term memory. Although this study highlights the importance of teaching literacy skills specifically attuned to science classes, further research is needed to assess whether a lack of genre knowledge accounts for the lack of identification of argument errors.

    J. Res. Reading 33, 54 (2010).

  7. Development

    Moving In and Settling Down

    1. Beverly A. Purnell

    In stem cell–based therapeutic strategies aimed at restoring the function of neural tissue, the proliferation, differentiation, and migration of introduced neural precursor cells must be tightly controlled. Delaloy et al. have examined microRNA (miRNA) expression as human embryonic stem cells differentiated into postmitotic neurons in cell culture and found that miRNA-9 (miR-9) increased in human neural progenitor cells (hNPCs) before terminal differentiation. In a mouse model of stroke, miR-9 loss of function resulted in a decrease of cell proliferation and an increase in migration of hNPCs that had been transplanted into ischemic mouse brain. Hence, miR-9 appears to coordinate early hNPC proliferation and delay early hNPC migration, properties that will be of use in designing potential treatments for brain or spinal cord injury.

    Cell Stem Cell 6, 323 (2010).

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