Evolution of block copolymer lithography to highly ordered square arrays     

Tang C  Lennon EM  Fredrickson GH  Kramer EJ  Hawker CJ 《Science (New York, N.Y.)》2008,322(5900):429-432

The manufacture of smaller, faster, more efficient microelectronic components is a major scientific and technological challenge, driven in part by a constant need for smaller lithographically defined features and patterns. Traditional self-assembling approaches based on block copolymer lithography spontaneously yield nanometer-sized hexagonal structures, but these features are not consistent with the industry-standard rectilinear coordinate system. We present a modular and hierarchical self-assembly strategy, combining supramolecular assembly of hydrogen-bonding units with controlled phase separation of diblock copolymers, for the generation of nanoscale square patterns. These square arrays will enable simplified addressability and circuit interconnection in integrated circuit manufacturing and nanotechnology.  相似文献   

Ice flow direction change in interior West Antarctica     

Siegert MJ  Welch B  Morse D  Vieli A  Blankenship DD  Joughin I  King EC  Vieli GJ  Payne AJ  Jacobel R 《Science (New York, N.Y.)》2004,305(5692):1948-1951

Upstream of Byrd Station (West Antarctica), ice-penetrating radar data reveal a distinctive fold structure within the ice, in which isochronous layers are unusually deep. The fold has an axis more than 50 kilometers long, which is aligned up to 45 degrees to the ice flow direction. Although explanations for the fold's formation under the present flow are problematic, it can be explained if flow was parallel to the fold axis approximately 1500 years ago. This flow change may be associated with ice stream alterations nearer the margin. If this is true, central West Antarctica may respond to future alterations more than previously thought.  相似文献   

Advanced cardiac morphogenesis does not require heart tube fusion     

Li S  Zhou D  Lu MM  Morrisey EE 《Science (New York, N.Y.)》2004,305(5690):1619-1622

The bilateral cardiac mesoderm migrates from the lateral region of the embryo to the ventral midline, where it fuses to form the primitive heart tube. It is generally accepted that migration and fusion are essential for subsequent stages of cardiac morphogenesis. We present evidence that, in Foxp4 mutant embryonic mice, each bilateral heart-forming region is capable of developing into a highly differentiated four-chambered mammalian heart in the absence of midline fusion. These data demonstrate that left-right chamber specification, cardiac looping, septation, cardiac myocyte differentiation, and endocardial cushion formation are preprogrammed in the precardiac mesoderm and do not require midline positional identity or heart tube fusion.  相似文献   

Virology. 1918 and all that     

Holmes EC 《Science (New York, N.Y.)》2004,303(5665):1787-1788

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Essential role of Fkbp6 in male fertility and homologous chromosome pairing in meiosis     

Crackower MA  Kolas NK  Noguchi J  Sarao R  Kikuchi K  Kaneko H  Kobayashi E  Kawai Y  Kozieradzki I  Landers R  Mo R  Hui CC  Nieves E  Cohen PE  Osborne LR  Wada T  Kunieda T  Moens PB  Penninger JM 《Science (New York, N.Y.)》2003,300(5623):1291-1295

Meiosis is a critical stage of gametogenesis in which alignment and synapsis of chromosomal pairs occur, allowing for the recombination of maternal and paternal genomes. Here we show that FK506 binding protein (Fkbp6) localizes to meiotic chromosome cores and regions of homologous chromosome synapsis. Targeted inactivation of Fkbp6 in mice results in aspermic males and the absence of normal pachytene spermatocytes. Moreover, we identified the deletion of Fkbp6 exon 8 as the causative mutation in spontaneously male sterile as/as mutant rats. Loss of Fkbp6 results in abnormal pairing and misalignments between homologous chromosomes, nonhomologous partner switches, and autosynapsis of X chromosome cores in meiotic spermatocytes. Fertility and meiosis are normal in Fkbp6 mutant females. Thus, Fkbp6 is a component of the synaptonemal complex essential for sex-specific fertility and for the fidelity of homologous chromosome pairing in meiosis.  相似文献   

Human-specific gain of function in a developmental enhancer     

Prabhakar S  Visel A  Akiyama JA  Shoukry M  Lewis KD  Holt A  Plajzer-Frick I  Morrison H  Fitzpatrick DR  Afzal V  Pennacchio LA  Rubin EM  Noonan JP 《Science (New York, N.Y.)》2008,321(5894):1346-1350

Changes in gene regulation are thought to have contributed to the evolution of human development. However, in vivo evidence for uniquely human developmental regulatory function has remained elusive. In transgenic mice, a conserved noncoding sequence (HACNS1) that evolved extremely rapidly in humans acted as an enhancer of gene expression that has gained a strong limb expression domain relative to the orthologous elements from chimpanzee and rhesus macaque. This gain of function was consistent across two developmental stages in the mouse and included the presumptive anterior wrist and proximal thumb. In vivo analyses with synthetic enhancers, in which human-specific substitutions were introduced into the chimpanzee enhancer sequence or reverted in the human enhancer to the ancestral state, indicated that 13 substitutions clustered in an 81-base pair module otherwise highly constrained among terrestrial vertebrates were sufficient to confer the human-specific limb expression domain.  相似文献   

Hybrid speciation in experimental populations of yeast     

Greig D  Louis EJ  Borts RH  Travisano M 《Science (New York, N.Y.)》2002,298(5599):1773-1775

Most models of speciation require gradual change and geographic or ecological isolation for new species to arise. Homoploid hybrid speciation occurred readily between Saccharomyces cerevisiae and Saccharomyces paradoxus. Hybrids had high self-fertility (about 82%), low fertility when backcrossed to either parental species (about 7.5%), and vigorous growth under different thermal environments that favored one or the other of the parental species. Extensive karyotypic changes (tetrasomy) were observed in the hybrids, although genic incompatibilities accounted for 50% of the variation in self-fertility.  相似文献   

Physics. Precision, not power     

Eyler EE 《Science (New York, N.Y.)》2011,333(6039):164-165

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Comment on "A bacterium that can grow by using arsenic instead of phosphorus"     

Cotner JB  Hall EK 《Science (New York, N.Y.)》2011,332(6034):1149; author reply 1149

Wolfe-Simon et al. (Research Articles, 3 June 2011, p. 1163; published online 2 December 2010) reported that bacterium GFAJ-1 can substitute arsenic for phosphorus in its macromolecules, including DNA and proteins. If such arseno-DNA exists, then much of the past century of work with arsenate and phosphate chemistry, as well as much of what we think we know about metabolism, will need rewriting.  相似文献   

Experimental evidence supports a sex-specific selective sieve in mitochondrial genome evolution     

Innocenti P  Morrow EH  Dowling DK 《Science (New York, N.Y.)》2011,332(6031):845-848

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