This Week in Science

Science  08 Nov 2013:
Vol. 342, Issue 6159, pp. 669
  1. Dissecting Hippo Interactions

    CREDIT: ARUNACHALAM VINAYAGAM AND YOUNG KWON

    The Hippo signaling pathway plays key roles in many processes, from cell proliferation and cell death to regulation of stem cells and cancer cells. Kwon et al. (p. 737, published 10 October) attempted to systematically identify all components of the pathway. A protein-protein interaction screen identified more than 200 interactions among approximately 150 proteins. A protein identified in the screen, Leash, restrained the activity of the transcriptional coactivator Yorkie, which regulates gene expression in response to Hippo signaling.

  2. Optomechanically Entangled

    Quantum entanglement allows engineered quantum systems to exceed classical information processing bounds. Palomaki et al. (p. 710, published online 3 October; see the Perspective by Hammerer) extend this quantum resource into the domain of micromechanical oscillators by demonstrating entanglement between a microwave field and a mechanical oscillator. The mechanical part of the entangled state could then be transferred to a second microwave field.

  3. Battery Breakdown

    Although a range of materials can be used for chemically storing electrical charge, many cannot be made into batteries that retain their capacity over many cycles. Failure may be because of secondary reactions, poisoning through the formation of surface coatings, or volumetric changes leading to fracture. Ebner et al. (p. 716, published online 17 October) studied this last scenario in an operating battery using synchrotron x-ray tomographic microscopy, tracking both the chemical changes in the battery and the resulting mechanical changes in a tin oxide model system, which is known to undergo large volume changes.

  4. Oxygen Control of Graphene Growth

    The growth of graphene on copper surfaces through the decomposition of hydrocarbons such as methane can result in a wide variety of crystal domain sizes and morphologies. Hao et al. (p. 720, published online 24 October; see the cover) found that the presence of surface oxygen could limit the number of nucleation sites and allowed centimeter-scale domains to grow through a diffusion-limited mechanism. The electrical conductivity of the graphene was comparable to that of exfoliated graphene.

  5. Which Side of the Moon?

    CREDIT: MILJKOVIĆ ET AL.

    The far- and nearsides of the Moon are geologically different. Using high-precision crustal thickness maps derived from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, Miljković et al. (p. 724) show that the distribution of lunar impact basins is also highly asymmetrical. Numerical simulations of impact basin formation coupled with three-dimensional simulations of the Moon's asymmetric thermal evolution suggest that lateral variations in temperature within the Moon's crust have a large effect on the final size of an impact basin.

  6. Lighting Up Immunity

    TH17 cells are CD4+ T helper cells that produce the proinflammatory cytokine interleukin-17. In the intestines, TH17 cells protect the host from fungal and bacterial infections, and their proinflammatory function is linked with autoimmune diseases including inflammatory bowel disease. Yu et al. (p. 727) show that the molecular circadian clock directly regulates the differentiation of TH17 cells in the intestine, which suggest that both nutrition and light are important environmental factors that directly regulate the immune response.

  7. Mitochondrial Fusion and Heart Development

    The role of mitochondria in fueling homeostatic cell processes is well appreciated, but whether and how they influence cell differentiation is much less clear. Using in vivo embryonic mouse models and mouse embryonic stem cell cultures, Kasahara et al. (p. 734, published online 3 October) found that an intact mitochondrial fusion pathway was essential for the cellular signaling that drives mesodermal cell differentiation into cardiomyocytes.

  8. Bridging the Titin Gap

    The muscle protein titin is a molecular spring that has been extensively studied by single-molecule unfolding experiments and by molecular simulation. However, experimental and simulated unfolding could not be compared directly because they differ by orders of magnitude in pulling velocity. Rico et al. (p. 741) developed high-speed force spectroscopy to pull titin molecules at speeds that reach the lower limits of molecular dynamics simulations. Bridging the gap between simulation and experiment clarified the mechanism of conformational changes in titin.

  9. DNA Differences

    The extent to which genetic variation affects an individual's phenotype has been difficult to predict because the majority of variation lies outside the coding regions of genes. Now, three studies examine the extent to which genetic variation affects the chromatin of individuals with diverse ancestry and genetic variation (see the Perspective by Furey and Sethupathy). Kasowski et al. (p. 750, published online 17 October) examined how genetic variation affects differences in chromatin states and their correlation to histone modifications, as well as more general DNA binding factors. Kilpinen et al. (p. 744, published online 17 October) document how genetic variation is linked to allelic specificity in transcription factor binding, histone modifications, and transcription. McVicker et al. (p. 747, published online 17 October) identified how quantitative trait loci affect histone modifications in Yoruban individuals and established which specific transcription factors affect such modifications.

  10. From Here to There

    CREDIT: NIETO ET AL.

    To form different tissues and organs, embryonic cells must migrate to new locations. Specific transcription factors, epigenetic and splicing programs, and microRNA regulatory networks regulate this process, which is known as the epithelial-to-mesenchymal transition (EMT). During EMT, considerable cellular plasticity is observed, and once activated at their new location, cells must again change into their new differentiated form. This “reverse” event is called the mesenchymal-to-epithelial transition (MET). Nieto (10.1126/science.1234850) reviews EMT and MET as observed during normal development and in the generation of cancer when cells leave the primary tumor and travel to other parts of the body forming metastases and secondary tumors.

  11. Pre-Initiation Complex in 3D

    The regulation of gene expression is critical for almost every aspect of biology. Transcription—generating an RNA copy of a gene—requires the assembly of a large pre-initiation complex (PIC) at every RNA polymerase II (pol II) promoter. Roughly 32 proteins—the subunits of pol II and the general transcription factors—form a PIC that can recognize a minimal TATA-box promoter, select a transcription start site, and synthesize a nascent transcript. Murakami et al. (10.1126/science.1238724, published online 26 September; see the Perspective by Malik and Roeder) determined the three-dimensional map of the Saccharomyces cerevisiae 30-subunit PIC using cryo-electron microscopy. The saddle-shaped TATA binding protein, the boot-shaped transcription factor IIA (TFIIA), and promoter DNA ∼27 bp downstream of the TATA-box could all be seen. Cross-linking and mass spectrometry was used to determine the spatial proximity of the 30 subunits, revealing that the PIC forms two lobes with TFIIF forming a bridge between them.

  12. Cold Thermoelectrics

    Thermoelectric effects—such as the creation of a voltage drop in response to a thermal gradient (known as the Seebeck effect)—can be used for a number of applications, including converting wasted heat into power. However, especially in solids that exhibit electronic interactions, this type of behavior is not well understood. Brantut et al. (p. 713, published online 24 October; see the Perspective by Heikkilä) studied the Seebeck effect in the very controllable setting of cold atomic gases. Two initially identical reservoirs of 6Li atoms were connected using a quasi–two-dimensional channel, and the particle current after heating one of the reservoirs was measured. The atoms moved from the warmer to the cooler reservoir, the extent of which fit with theoretical predictions as the disorder in the channel and its geometry were varied.

  13. Caulobacter Chromosome

    Chromosomal DNA must be highly compacted to fit within the tiny volume of the cell, while at the same time it must maintain a conformation that allows critical cellular processes access to the genome. Le et al. (p. 731, published online 24 October) analyzed the structure of the circular chromosome in the prokaryote Caulobacter crescentus by using chromosome conformation capture and deep-sequencing. Highly self-interacting regions (chromosomal interaction domains, or CIDs) were observed—similar to the topologically associated domains previously seen in eukaryotes. Supercoiling helped to establish CIDs, and CID boundaries were defined by highly expressed genes. CIDs appeared to be established during or shortly after DNA replication, and could potentially facilitate chromosomal segregation by preventing newly replicated chromosomes from becoming entangled.

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