Editors' Choice

Science  13 Feb 2009:
Vol. 323, Issue 5916, pp. 854

    Focusing on Flowers

    1. Laura M. Zahn

    Transcription factors play many important roles in flowering plants, including the spatial and temporal regulation of highly conserved events in floral development. Urbanus et al. have mapped the localization of four such factors—AGAMOUS, SEPALLATA3, APETALA1, and FRUITFUL-that contain MADS domains and are associated with floral organ development in Arabidopsis. Their results show that gene expression patterns, as assessed by mRNA, are not fully correlated with protein expression, suggesting that these transcription factors are acting in a non-cell-autonomous manner. Furthermore, these data support the view that information gained via protein localization can be used in concert with mRNA measurements in analyzing developmental trajectories. — LMZ

    BMC Plant Biol. 9, 5 (2009).


    Postponing Senescence

    1. Beverly A. Purnell

    Although aging affects us all, concerns about reproductive aging generally refer to females. But females have not cornered this market: Reproductive aging in men is evidenced by decreased fertility that correlates with decreased testosterone and sperm motility. Likewise, rodent studies reveal compromised reproduction with advancing age, and rodent male reproductive success has been shown, in some studies, to be affected by environmental factors such as the presence of females or social isolation.

    Schmidt et al. have documented a fertility effect on male mice aging either in isolation or in cohabitation with females. Naïve females were bred with 16- to 32-month old males in cohorts spaced 2 months apart. A significant effect was seen: Males separated from females were less fertile by 26 months, and this correlated with the onset of abnormal spermatogenesis. On the other hand, fertility was not affected in males up to 32 months if they had been housed with females. Hence, reproductive aging is delayed when females are present, and this delay represents a 20% extension of the normal period of fertility. Nevertheless, when fertility begins to decrease, it does so at the same rate regardless of social environment. These data on male reproductive aging may influence the management of livestock and endangered species as well as provoking discussion about human fertility. — BAP

    Biol. Reprod. 80, 10.1095/biolreprod.108.073619 (2009).


    Sulfur in Oil ...

    1. Julia Fahrenkamp-Uppenbrink

    Before crude oil can be used as a fuel or chemical feedstock, it must first be separated into different fractions, which are typically classified according to their viscosity. These must then be cleaned up; for example, to remove sulfur. Heavier fractions often contain more sulfur in the form of polycyclic aromatic sulfur heterocycles, which are difficult to remove with existing catalytic processes. To improve these processes, it is important to sift out knowledge about the molecular structures containing the sulfur from the highly complex overall mixture. Panda et al. have used a range of different ionization techniques, in conjunction with chromatography and mass spectrometry, to characterize the types and classes of sulfur-containing polyaromatic molecules in a crude oil fraction. Each ionization technique favors some molecules but discriminates against others, thus providing different windows for studying the system. Use of any one technique in isolation might therefore bias the results, but used in conjunction, they can elucidate the complex composition of crude oil and may inform the development of better sulfur-removal processes. — JFU

    Angew. Chem. Int. Ed. 48, 10.1002/anie.200803403 (2009).


    ... and Sulfur on Mars

    1. Brooks Hanson

    Recent observations from satellites and the rovers shows that Mars has abundant sulfate minerals on its surface and that acidic alteration is widespread (carbonate minerals are rare). This is in marked contrast to the composition of even older rocks on Earth and the generally low sulfur content of Earth's crust. Gaillard and Scaillet show that these differences reflect the nature of each planet's internal and atmospheric evolution. Because of the lower overall pressure on Mars and its different core size and composition, the Martian mantle probably contains considerably more iron than Earth's. As a result, magmas derived from the mantle on Mars are several times richer in sulfur. Furthermore, low atmospheric pressure favors efficient degassing of this sulfur. The authors argue that thus as the atmosphere of Mars was lost to space, with pressure dropping from initial high values, its composition changed from water- and CO2-rich to sulfate-rich. This evolution can explain the observed history in which neutral hydrothermal alteration is superseded by widespread acidic alteration, and there is sufficient sulfur to cover the surface thickly in sulfate minerals. — BH

    Earth Planet. Sci. Lett. 10.1016/j.epsl.2008.12.028 (2009).


    Precision Prescription

    1. Paula A. Kiberstis

    Physicians have long recognized that a therapeutic drug eliciting the desired response in one patient (maximal efficacy for the disorder being treated, with minimal side effects) may achieve only a suboptimal response in another patient. Because genetic differences can contribute to variation across individuals in drug responsiveness, there is growing interest in the idea that gene-based or pharmacogenomic tests might allow a better matching of drugs and drug dosages to individual patients.

    Progress along these lines is described by three independent groups that have studied the drug clopidogrel, an inhibitor of blood clots that is commonly prescribed for patients after a heart attack in order to reduce the chance of subsequent coronary events. Clopidogrel is a pro-drug and is inactive until it is metabolized in the liver by cytochrome P450 enzymes, including CYP2C19. In two large studies involving 1500 to 2200 clopidogrel-treated patients who were monitored for 12 to 15 months, Mega et al. and Simon et al. found that individuals who carried one or two variant alleles of CYP2C19 that confer loss of enzyme function were 1.5 to 3.5 times more likely to die or experience cardiovascular-related complications than patients who carried high-functioning alleles. Collet et al. reported broadly similar results in a smaller study of 250 clopidogrel-treated patients who had suffered a heart attack at a young age. The consistency of the outcomes seen in these studies is promising and may set the stage for a prospective clinical trial designed to assess whether CYP2C19 genotyping would add a new chapter to the physician's pharmacopoeia. — PAK

    New Engl. J. Med. 360, 354; 363 (2009); Lancet 373, 309 (2009).


    Journey to the Center of the Cell

    1. Helen Pickersgill

    The levels of epithelial cell adhesion molecule (EpCAM) are up-regulated in various human carcinomas, suggesting that it may play a role in tumor cell proliferation. EpCAM is a transmembrane glycoprotein found at the plasma membrane and is thought to function primarily in cell adhesion. Maetzel et al. found that EpCAM was subject to proteolytic cleavage by the proteases TACE and presenilin-2. The clipped-off intracellular domain (EpICD) was released from the membrane and moved into the nucleus, where it formed a DNA-bound complex with Lef-1 and β-catenin, which is a downstream effector of the Wnt pathway that is known to be involved in cell renewal and is commonly deregulated in cancer. Both EpCAM and EpICD were able to induce tumor formation in immunodeficient mice, and human colon carcinoma cells contained nuclear EpICD whereas normal colon cells did not. These results suggest that regulated intramembrane proteolysis may mediate an EpCAM signaling cascade from the cell membrane to the nucleus. — HP*

    Nat. Cell Biol. 11, 162 (2009).

    • *Helen Pickersgill is a locum editor in Science's editorial department.


    A Colloidal Erector Set

    1. Marc S. Lavine

    Colloidal particles are often used as analogs to atoms for studying the glassy behavior and crystallization of solids. Just as atoms bond together to form molecules with a range of bond types and strengths, Kraft et al. brought colloidal particles together with variations in the bonding motifs. Specifically, they used cross-linked polystyrene particles that were swollen with styrene monomer, causing the monomer to phase-separate and form a protrusion on the surface of the particle. Through variations in the swelling ratio of the particle or the hydrophilicity of the particle surface, the expelled monomer could be tuned to either fully coat the particle or to form an aspherical protrusion at only one place on the surface. When these colloidal particles in solution interacted with each other, the liquid protrusions merged and could be subsequently polymerized, bonding the particles together. The overall shape depended on the ratio of monomer to particle. — MSL

    J. Am. Chem. Soc. 131, 10.1021/ja8079803 (2009).