Induction of tumors in mice by genomic hypomethylation   总被引：1，自引：0，他引：1  

Gaudet F  Hodgson JG  Eden A  Jackson-Grusby L  Dausman J  Gray JW  Leonhardt H  Jaenisch R 《Science (New York, N.Y.)》2003,300(5618):489-492

Genome-wide DNA hypomethylation occurs in many human cancers, but whether this epigenetic change is a cause or consequence of tumorigenesis has been unclear. To explore this phenomenon, we generated mice carrying a hypomorphic DNA methyltransferase 1 (Dnmt1) allele, which reduces Dnmt1 expression to 10% of wild-type levels and results in substantial genome-wide hypomethylation in all tissues. The mutant mice were runted at birth, and at 4 to 8 months of age they developed aggressive T cell lymphomas that displayed a high frequency of chromosome 15 trisomy. These results indicate that DNA hypomethylation plays a causal role in tumor formation, possibly by promoting chromosomal instability.  相似文献   

Deciphering the reaction dynamics underlying optimal control laser fields     

Daniel C  Full J  González L  Lupulescu C  Manz J  Merli A  Vajda S  Wöste L 《Science (New York, N.Y.)》2003,299(5606):536-539

Femtosecond high-resolution pump-probe experiments have been used together with theoretical ab initio quantum calculations and wave packet dynamics simulations to decode an optimal femtosecond pulse that is generated from adaptive learning algorithms. This pulse is designed to maximize the yield of the organometallic ion CpMn(CO)3 while hindering the competing fragmentation. The sequential excitation and ionization of the target ion are accomplished by an optimized field consisting of two dominant subpulses with optimal frequencies and time delays.  相似文献   

Genome research. A tussle over the rules for DNA data sharing     

Roberts L 《Science (New York, N.Y.)》2002,298(5597):1312-1313

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HST and VLT investigations of the fragments of comet C/1999 S4 (LINEAR)     

Weaver HA  Sekanina Z  Toth I  Delahodde CE  Hainaut OR  Lamy PL  Bauer JM  A'Hearn MF  Arpigny C  Combi MR  Davies JK  Feldman PD  Festou MC  Hook R  Jorda L  Keesey MS  Lisse CM  Marsden BG  Meech KJ  Tozzi GP  West R 《Science (New York, N.Y.)》2001,292(5520):1329-1333

At least 16 fragments were detected in images of comet C/1999 S4 (LINEAR) taken on 5 August 2000 with the Hubble Space Telescope (HST) and on 6 August with the Very Large Telescope (VLT). Photometric analysis of the fragments indicates that the largest ones have effective spherical diameters of about 100 meters, which implies that the total mass in the observed fragments was about 2 x 10(9) kilograms. The comet's dust tail, which was the most prominent optical feature in August, was produced during a major fragmentation event, whose activity peaked on UT 22.8 +/- 0.2 July 2000. The mass of small particles (diameters less than about 230 micrometers) in the tail was about 4 x 10(8) kilograms, which is comparable to the mass contained in a large fragment and to the total mass lost from water sublimation after 21 July 2000 (about 3 x 10(8) kilograms). HST spectroscopic observations during 5 and 6 July 2000 demonstrate that the nucleus contained little carbon monoxide ice (ratio of carbon monoxide to water is less than or equal to 0.4%), which suggests that this volatile species did not play a role in the fragmentation of C/1999 S4 (LINEAR).  相似文献   

Principles for the buffering of genetic variation     

Hartman JL  Garvik B  Hartwell L 《Science (New York, N.Y.)》2001,291(5506):1001-1004

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Specific mutations induced by triplex-forming oligonucleotides in mice     

Vasquez KM  Narayanan L  Glazer PM 《Science (New York, N.Y.)》2000,290(5491):530-533

Triplex-forming oligonucleotides (TFOs) recognize and bind to specific duplex DNA sequences and have been used extensively to modify gene function in cells. Although germ line mutations can be incorporated by means of embryonic stem cell technology, little progress has been made toward introducing mutations in somatic cells of living organisms. Here we demonstrate that TFOs can induce mutations at specific genomic sites in somatic cells of adult mice. Mutation detection was facilitated by the use of transgenic mice bearing chromosomal copies of the supF and cII reporter genes. Mice treated with a supF-targeted TFO displayed about fivefold greater mutation frequencies in the supF gene compared with mice treated with a scrambled sequence control oligomer. No mutagenesis was detected in the control gene (cII) with either oligonucleotide. These results demonstrate that site-specific, TFO-directed genome modification can be accomplished in intact animals.  相似文献   

SCIENCE CAREERS: Geoscientists in High Demand in the Oil Industry     

Laursen L 《Science (New York, N.Y.)》2008,321(5890):857-859

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Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry     

Trotter JA  Williams IS  Barnes CR  Lécuyer C  Nicoll RS 《Science (New York, N.Y.)》2008,321(5888):550-554

The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth's history. Previous temperature estimates of up to approximately 70 degrees C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician-Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.  相似文献   

Body-centered cubic iron-nickel alloy in Earth's core   总被引：1，自引：0，他引：1  

Dubrovinsky L  Dubrovinskaia N  Narygina O  Kantor I  Kuznetzov A  Prakapenka VB  Vitos L  Johansson B  Mikhaylushkin AS  Simak SI  Abrikosov IA 《Science (New York, N.Y.)》2007,316(5833):1880-1883

Cosmochemical, geochemical, and geophysical studies provide evidence that Earth's core contains iron with substantial (5 to 15%) amounts of nickel. The iron-nickel alloy Fe(0.9)Ni(0.1) has been studied in situ by means of angle-dispersive x-ray diffraction in internally heated diamond anvil cells (DACs), and its resistance has been measured as a function of pressure and temperature. At pressures above 225 gigapascals and temperatures over 3400 kelvin, Fe(0.9)Ni(0.1) adopts a body-centered cubic structure. Our experimental and theoretical results not only support the interpretation of shockwave data on pure iron as showing a solid-solid phase transition above about 200 gigapascals, but also suggest that iron alloys with geochemically reasonable compositions (that is, with substantial nickel, sulfur, or silicon content) adopt the bcc structure in Earth's inner core.  相似文献   

The structure of ferrihydrite, a nanocrystalline material   总被引：2，自引：0，他引：2  

Michel FM  Ehm L  Antao SM  Lee PL  Chupas PJ  Liu G  Strongin DR  Schoonen MA  Phillips BL  Parise JB 《Science (New York, N.Y.)》2007,316(5832):1726-1729

Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, the nanocrystallinity of this iron oxyhydroxide has hampered accurate structure determination by traditional methods that rely on long-range order. We uncovered the atomic arrangement by real-space modeling of the pair distribution function (PDF) derived from direct Fourier transformation of the total x-ray scattering. The PDF for ferrihydrite synthesized with the use of different routes is consistent with a single phase (hexagonal space group P6(3)mc; a = approximately 5.95 angstroms, c = approximately 9.06 angstroms). In its ideal form, this structure contains 20% tetrahedrally and 80% octahedrally coordinated iron and has a basic structural motif closely related to the Baker-Figgis delta-Keggin cluster. Real-space fitting indicates structural relaxation with decreasing particle size and also suggests that second-order effects such as internal strain, stacking faults, and particle shape contribute to the PDFs.  相似文献