Editors' Choice

Science  22 Aug 2014:
Vol. 345, Issue 6199, pp. 887
  1. Neuroscience

    Tissue mimics brain's cortical layers

    1. EU

    Brainlike tissue is a practical test bed


    They may look like Play-Doh, but these colorful spongy rings are alive and may one day even learn. Tang-Schomer et al. engineered the rings to mimic the structure and function of the six layers of human cortical brain tissue. The researchers coaxed the neurons to grow around a matrix of silk proteins immersed in collagen gel. The cells cling to the structure as they branch out and connect, forming 3D networks resembling real neural circuits, the authors say. The team hopes to keep the neuronal sponge alive for 6 months, longer than any previous model, to study how its neural networks respond to insults such as disease or traumatic injury, and perhaps to see if its activity is altered by experience, a form of learning.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1324214111.(2014).

  2. Cancer Treatment

    How to boost cancer immunotherapy

    1. Paula A. Kiberstis

    Why does our immune system protect us so well against infection but not against cancer? In part, this is because cancer cells use clever ways to escape immune responses designed to destroy them. A therapeutic strategy called “immune checkpoint blockade” thwarts these escape tactics and renders cancer cells vulnerable to immune attack. Although remarkably effective, only a subset of patients respond to it. Seeking possible explanations for this limited response, Kim et al. identified a specific immune cell population that interferes with the therapy in mouse tumor models. When the authors coadministered drugs that reduced the levels of these cells (called myeloid-derived suppressor cells), the efficacy of immune checkpoint blockade therapy greatly improved.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1410626111 (2014).

  3. Education

    Students produce assessment materials

    1. Melissa McCartney

    If teaching someone else is the best way to learn, what will students gain from writing their own test questions? Every week, as part of an introductory undergraduate physics class, Bates et al. required students to contribute one original test question, answer five others, and critique an additional three. The researchers used Bloom's taxonomy criteria for cognitive level and quality of explanation—a standard scale—to rate the questions. Seventy-five percent of questions produced by first-year students were of high quality, with a large portion of the questions constituting true problems, as opposed to simple multiple choice questions. Overall, involving students in the summative assessment strategy for their own course increased both engagement and learning.

    Phys. Rev. ST Phys. Educ. Res. 10.1103/PhysRevSTPER.10.020105 (2014).

  4. Environmental Science

    How much methane from landfills?

    1. Julia Fahrenkamp-Uppenbrink

    Landfill sites emit substantial amounts of the greenhouse gas methane, but how much of the methane in the atmosphere comes from such sites? Scientists have measured widely varying fluxes, so estimates have been highly uncertain. Xu et al. measured methane emissions from a landfill site in Lincoln, Nebraska, from June to December 2010. They found that emissions varied widely from one day to the next, depending on the air pressure: The higher the air pressure, the lower the emissions. They conclude that measurements must be taken for at least 10 days to obtain a good estimate of annual methane emissions from landfill sites. This conclusion also could apply to other environmental sources of methane, such as wetlands and peatlands.

    Methane emission varies daily at landfills


    Global Biogeochem. Cy. 10.1002/2013GB004571 (2014).

  5. Stem Cell Number

    Counting human intestinal stem cells

    1. Beverly A. Purnell

    The cells that line the intestine, called intestinal epithelial cells, turn over, meaning that old ones die and new ones take their place. Stem cells located at the base of fingerlike structures called intestinal crypts support this high rate of turnover. Baker et al. investigated how this process works using human cells. The authors traced the lineage of cells in human intestinal crypts by counting naturally occurring mitochondrial DNA mutations. They identified five to six stem cells per crypt, which itself divides about once every 30 to 40 years. People who had a mutation in the APC gene, common in colon cancer, had more stem cells, and their crypts divided at a faster rate.

    Cell Rep. 10.1016/j.celrep.2014.07.019 (2014).

  6. Mycobacteria

    Bacteria scrimp and save themselves

    1. Caroline Ash

    Proteasomes are large protein complexes that degrade cellular proteins. Although widely conserved in mammals, only some bacteria species have machinery resembling the mammalian system (called Pup in bacteria). But why? In Mycobacterium tuberculosis, Pup contributes to virulence. Elharar et al. now report that in order to survive starvation, non-virulent mycobacteria need Pup too. If nitrogen supplies are low (nitrogen is key for mycobacteria growth), the Pup machinery will chew up some of the bacterium's own proteins to recycle amino acids. This diverts amino acids into maintaining basic metabolism until, hopefully, living conditions improve.

    EMBO J. 10.15252/embj.201387076 (2014).

  7. Astrophysics

    Giants in the outer halo of the Milky Way

    1. Margaret M. Moerchen

    Most stars in the Milky Way reside in the familiar spiral disk structure and probably formed in place. Stars in the galaxy's much larger and far sparser spherical halo, on the other hand, are unlikely to have formed where the gas density is so low. Too few halo stars are known, however, for scientists to model their origins. Bochanski et al. examined the motion and brightness of some candidate stars, and identified two that are the most distant members of our galaxy yet found, more than 30 times farther from the galactic center than the Sun. These observations should help tell whether these stars were captured from dwarf galaxies or ejected from the Milky Way disk.

    Astrophys. J. Lett. 10.1088/2041-8205/790/1/L5 (2014).

  8. Animal Communication

    Bat calls shaped by sexual selection

    1. Sacha Vignieri

    Frequency matters in bat calls


    Animals use a variety of signals to communicate, especially during mating. Bats, however, face an unusual problem. Using visual signals is challenging because they are nocturnal; and because they use calls to locate food, food demands constrain how these calls can evolve. Peuchmaille et al. now report that sexual selection shapes the calls of Meheley's horseshoe bats. They found that the frequency of males' calls indicated their size and that females preferred the higher-frequency calls emitted by larger males. Furthermore, these larger males sired more offspring. Higherfrequency calls may make these bats less efficient at tracking food, which suggests that the calls evolved in response to countervailing constraints.

    PLOS One 10.1371/journal.pone.0103452 (2014).