Materials science. Sweet, hairy, soft, and slippery     

Lee S  Spencer ND 《Science (New York, N.Y.)》2008,319(5863):575-576

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Synthetic clonal reproduction through seeds     

Marimuthu MP  Jolivet S  Ravi M  Pereira L  Davda JN  Cromer L  Wang L  Nogué F  Chan SW  Siddiqi I  Mercier R 《Science (New York, N.Y.)》2011,331(6019):876

Cloning through seeds has potential revolutionary applications in agriculture, because it would allow vigorous hybrids to be propagated indefinitely. However, asexual seed formation or apomixis, avoiding meiosis and fertilization, is not found in the major food crops. To develop de novo synthesis of apomixis, we crossed Arabidopsis MiMe and dyad mutants that produce diploid clonal gametes to a strain whose chromosomes are engineered to be eliminated after fertilization. Up to 34% of the progeny were clones of their parent, demonstrating the conversion of clonal female or male gametes into seeds. We also show that first-generation cloned plants can be cloned again. Clonal reproduction through seeds can therefore be achieved in a sexual plant by manipulating two to four conserved genes.  相似文献   

Four climate cycles of recurring deep and surface water destabilizations on the Iberian margin     

Martrat B  Grimalt JO  Shackleton NJ  de Abreu L  Hutterli MA  Stocker TF 《Science (New York, N.Y.)》2007,317(5837):502-507

Centennial climate variability over the last ice age exhibits clear bipolar behavior. High-resolution analyses of marine sediment cores from the Iberian margin trace a number of associated changes simultaneously. Proxies of sea surface temperature and water mass distribution, as well as relative biomarker content, demonstrate that this typical north-south coupling was pervasive for the cold phases of climate during the past 420,000 years. Cold episodes after relatively warm and largely ice-free periods occurred when the predominance of deep water formation changed from northern to southern sources. These results reinforce the connection between rapid climate changes at Mediterranean latitudes and century-to-millennial variability in northern and southern polar regions.  相似文献   

Transgenerational epigenetic instability is a source of novel methylation variants     

Schmitz RJ  Schultz MD  Lewsey MG  O'Malley RC  Urich MA  Libiger O  Schork NJ  Ecker JR 《Science (New York, N.Y.)》2011,334(6054):369-373

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Relationship between clinical signs and transmission of an infectious disease and the implications for control     

Charleston B  Bankowski BM  Gubbins S  Chase-Topping ME  Schley D  Howey R  Barnett PV  Gibson D  Juleff ND  Woolhouse ME 《Science (New York, N.Y.)》2011,332(6030):726-729

Control of many infectious diseases relies on the detection of clinical cases and the isolation, removal, or treatment of cases and their contacts. The success of such "reactive" strategies is influenced by the fraction of transmission occurring before signs appear. We performed experimental studies of foot-and-mouth disease transmission in cattle and estimated this fraction at less than half the value expected from detecting virus in body fluids, the standard proxy measure of infectiousness. This is because the infectious period is shorter (mean 1.7 days) than currently realized, and animals are not infectious until, on average, 0.5 days after clinical signs appear. These results imply that controversial preemptive control measures may be unnecessary; instead, efforts should be directed at early detection of infection and rapid intervention.  相似文献   

Ordered and dynamic assembly of single spliceosomes     

Hoskins AA  Friedman LJ  Gallagher SS  Crawford DJ  Anderson EG  Wombacher R  Ramirez N  Cornish VW  Gelles J  Moore MJ 《Science (New York, N.Y.)》2011,331(6022):1289-1295

The spliceosome is the complex macromolecular machine responsible for removing introns from precursors to messenger RNAs (pre-mRNAs). We combined yeast genetic engineering, chemical biology, and multiwavelength fluorescence microscopy to follow assembly of single spliceosomes in real time in whole-cell extracts. We find that individual spliceosomal subcomplexes associate with pre-mRNA sequentially via an ordered pathway to yield functional spliceosomes and that association of every subcomplex is reversible. Further, early subcomplex binding events do not fully commit a pre-mRNA to splicing; rather, commitment increases as assembly proceeds. These findings have important implications for the regulation of alternative splicing. This experimental strategy should prove widely useful for mechanistic analysis of other macromolecular machines in environments approaching the complexity of living cells.  相似文献   

The genome of the diatom Thalassiosira pseudonana: ecology, evolution, and metabolism     

Armbrust EV  Berges JA  Bowler C  Green BR  Martinez D  Putnam NH  Zhou S  Allen AE  Apt KE  Bechner M  Brzezinski MA  Chaal BK  Chiovitti A  Davis AK  Demarest MS  Detter JC  Glavina T  Goodstein D  Hadi MZ  Hellsten U  Hildebrand M  Jenkins BD  Jurka J  Kapitonov VV  Kröger N  Lau WW  Lane TW  Larimer FW  Lippmeier JC  Lucas S  Medina M  Montsant A  Obornik M  Parker MS  Palenik B  Pazour GJ  Richardson PM  Rynearson TA  Saito MA  Schwartz DC  Thamatrakoln K  Valentin K  Vardi A  Wilkerson FP  Rokhsar DS 《Science (New York, N.Y.)》2004,306(5693):79-86

Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for approximately 20% of global carbon fixation. We report the 34 million-base pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand-base pair mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, use of a range of nitrogenous compounds, and a complete urea cycle, all attributes that allow diatoms to prosper in aquatic environments.  相似文献   

Naturally occurring antibodies reactive with sperm proteins: apparent deficiency in AIDS sera   总被引：3，自引：0，他引：3  

T C Rodman  J Laurence  F H Pruslin  N Chiorazzi  R Winston 《Science (New York, N.Y.)》1985,228(4704):1211-1215

A set of naturally occurring immunoglobulin M (IgM) antibodies that are reactive with a defined subset of proteins in the acrosomal cap region of human sperm has been identified. These antibodies are present in a broad spectrum of human sera from males and females, 1 day to 40 years of age, and are absent or markedly deficient in a large proportion of sera from individuals with the acquired immune deficiency syndrome (AIDS) or at risk for AIDS. The subset of proteins with which the IgM antibodies are reactive includes a factor (or factors) capable of inhibiting lectin-induced T-lymphocyte proliferation. The prevalence of the sperm-reactive IgM antibodies indicates that they are not elicited by sperm. Further, immunoreactivity of the sperm proteins resulting in depletion of specific circulating IgM antibodies, or other interactions between the sperm proteins and elements of the immune system, may be a factor in the suppressed state of the immune system in AIDS.  相似文献   

Bioaccumulation of melamine in catfish muscle following continuous, low-dose, oral administration     

Andersen WC  Turnipseed SB  Karbiwnyk CM  Evans E  Hasbrouck N  Mayer TD  Gieseker CM  Nochetto C  Stine CB  Reimschuessel R 《Journal of agricultural and food chemistry》2011,59(7):3111-3117

In this study, catfish muscle was analyzed for melamine (MEL) and cyanuric acid (CYA) residues following experimental feeding with low doses of MEL and MEL and CYA (MEL+CYA) and with the insoluble melamine-cyanurate complex (MEL=CYA). Catfish were daily fed 0.1 mg/kg BW of MEL for 15, 28, or 42 days, 0.1 mg/kg BW of MEL+CYA for 28 days, 2.5 mg/kg BW of MEL+CYA for 14 days, or 400 mg/kg BW of MEL=CYA for 3 days. Residues in the tissue were determined by LC-MS/MS. MEL was extracted with acidic acetonitrile, followed by defatting with dichloromethane, and isolated with cation exchange solid phase extraction (SPE). For CYA analysis, fish were extracted with dilute acetic acid, defatted with hexane, and cleaned up with a graphitic carbon SPE. Catfish fed 0.1 mg/kg BW of MEL reached a maximum muscle residue concentration of 0.33 ± 0.04 mg/kg (ppm) after 28 days of continuous feeding. The same concentration was found for MEL+CYA feeding at the 0.1 mg/kg BW level for 28 days. Feeding at 2.5 mg/kg BW of MEL+CYA yielded muscle concentrations above the 2.5 mg/kg level of concern for most of the study fish. Finally, catfish fed high levels of the MEL=CYA complex (400 mg/kg BW) accumulated relatively little MEL in the muscle (0.14 ± 0.07 mg/kg) and, unlike treatment with MEL+CYA, did not form renal melamine-cyanurate crystals. Appreciable concentrations of CYA were not detected in any of the muscles tested. These studies provide data to model the bioaccumulation of triazine residues into edible fish tissue as a result of the continuous consumption of adulterated feed.  相似文献   

Earthworm indicators as tools for soil monitoring,characterization and risk assessment. An example from the national Bioindicator programme (France)     

Guénola Pérès  Franck Vandenbulcke  Muriel Guernion  Mickaël Hedde  Thierry Beguiristain  Francis Douay  Sabine Houot  Denis Piron  Antoine Richard  Antonio Bispo  Cécile Grand  Laurence Galsomies  Daniel Cluzeau 《Pedobiologia》2011

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