Editors' Choice

Science  09 Nov 2012:
Vol. 338, Issue 6108, pp. 723
  1. Materials Science

    Factoring the Growth

    1. Marc S. Lavine
    CREDIT: KIRT L. ONTHANK/WIKIMEDIA COMMONS

    Many organisms, including diatoms, create very complex single-crystal mineral structures, whose shaping and patterning are regulated by a small number of proteins. It has been a challenge to decipher which proteins are fundamental to the process, and conversely, how close to the biological shapes one can get by growing the crystals in vitro using only a limited set of proteins. For sea urchins, the construction of the magnesian calcite endoskeleton is controlled by a single cell type—the primary mesenchyme cells (PMCs). Knapp et al. exploited this well-defined system to explore the role of recombinant vascular endothelial growth factor (rVEGF), which acts as a signaling molecule, on the shape and crystallography of the spicules that form when the PMCs are cultured in vitro. At low concentrations of rVEGF, linear spicules formed with growth parallel to the calcite c axis, but at much higher concentrations a triple branch point formed, with elongated arms growing parallel to the a-axis. Close to the branch point, the three arms were 120° apart, but these angles changed once the arms grew past 7 µm, which may explain why in sea urchins they are limited to 3 to 5 µm in size.

    J. Am. Chem. Soc. 10.1021/ja309024b (2012).

  2. Chemistry

    Click Your Nanoparticles

    1. Phil Szuromi

    Polymer nanoparticles are frequently tailored for particular applications by the type of functional groups displayed on their surface. Often the identification of the best functional group or groups can be an iterative process that can be slowed down by inefficient synthesis processes. Zhang et al. streamlined nanoparticle synthesis with diblock copolymers that were made by the ultrafast ring-opening polymerization of cyclic phospholane monomers. One monomer, bearing a 2-ethylbutyl group, forms a hydrophobic core, and the other, bearing a 3-butynyl group, has an alkyne functionality that allows for subsequent derivatization with a click reaction—photomediated, radical-mediated, thiol-yne chemistry. A variety of side chains—nonionic, anionic, cationic, and zwitterionic—could be added to the diblock copolymers. Introduction into water created micelles 13 to 21 nm in diameter with a polydispersity index below 1.2. The entire synthesis could be completed for the nonionic and anionic nanoparticles in two reaction vessels in 6 hours.

    J. Am. Chem. Soc. 10.1021/ja309037m (2012).

  3. Biomedicine

    Melanoma: Beyond the Light

    1. Paula A. Kiberstis

    Despite successful implementation of strategies that reduce exposure to ultraviolet radiation, the incidence of melanoma—the least common but most fatal form of skin cancer—continues to rise. This observation, together with the fact that melanomas can occur on non–sun-exposed skin, indicates that additional mechanisms independent of ultraviolet light contribute to tumorigenesis.

    CREDIT: ISTOCKPHOTO

    A new mechanistic clue has emerged from a mouse study designed to investigate why people with red hair and fair skin have the highest risk of developing melanoma. One distinguishing characteristic of these individuals is that they produce the red/yellow pigment pheomelanin. Mitra et al. found that genetically manipulated mice with pigmentation mimicking the human red-hair trait developed invasive melanoma at a higher rate than did mice with pigmentation mimicking dark-skinned humans, even in the absence of exposure to ultraviolet radiation. Selective ablation of pheomelanin synthesis by introduction of an albino allele protected the mice against melanoma. This suggests that pheomelanin itself plays a causal role in melanoma development, at least in mice, possibly by inducing oxidative damage to skin cells.

    Nature 10.1038/nature11624 (2012).

  4. Development

    Understanding the Niche

    1. Beverly A. Purnell

    Stem cells have the special ability to self-renew or undergo preprogrammed differentiation. The stem cell niche plays an important role in regulating this decision. If self-renewal proceeds uncontrollably, tumors can result. In the testes of Drosophila, a model used to understand niche–stem cell interactions, the niche is composed of the apical hub, which is important for the regulated division of its two stem cell populations: the germline stem cells (GSCs) and the cyst stem cells (CySCs). Prior studies had suggested that CySCs also serve as a niche to maintain GSCs; however, Lim and Fuller showed that after ablation of the CySCs and their progeny, early germ cells with GSC characteristics were still maintained. In particular, cells located near the apical hub were able to maintain the properties of GSCs in the absence of CySCs. Although the CySCs and cyst cells were not needed to maintain GSCs, they were necessary for their progression to the transit-amplifying stage, where the cells go through mitotic divisions before terminal differentiation. Hence, contrary to some prior conclusions, CySCs are not needed for GSC self-renewal but instead may provide signals to allow their progression through the transit-amplifying–stage divisions. This work highlights the intricate nature of the relationships between stem cells and the surrounding somatic cells.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1215516109 (2012).

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