Microfluidic systems: high radial acceleration in microvortices

Microfluidic systems can conveniently be used for rapid analysis of biological samples. Here we describe a single re-circulating flow, or microvortex, that can generate a maximum fluid rotational velocity of up to 12 m s(-1) and a corresponding radial acceleration in excess of 10(6)g. Such microvortices may be exploited in centrifugal microdevices to investigate the effects of high radial acceleration on biological and chemical processes.     

A gravitationally lensed quasar with quadruple images separated by 14.62 arcseconds

Gravitational lensing is a powerful tool for the study of the distribution of dark matter in the Universe. The cold-dark-matter model of the formation of large-scale structures (that is, clusters of galaxies and even larger assemblies) predicts the existence of quasars gravitationally lensed by concentrations of dark matter so massive that the quasar images would be split by over 7 arcsec. Numerous searches for large-separation lensed quasars have, however, been unsuccessful. All of the roughly 70 lensed quasars known, including the first lensed quasar discovered, have smaller separations that can be explained in terms of galaxy-scale concentrations of baryonic matter. Although gravitationally lensed galaxies with large separations are known, quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. Here we report the discovery of a lensed quasar, SDSS J1004 + 4112, which has a maximum separation between the components of 14.62 arcsec. Such a large separation means that the lensing object must be dominated by dark matter. Our results are fully consistent with theoretical expectations based on the cold-dark-matter model.     

Somatic integration and long-term transgene expression in normal and haemophilic mice using a DNA transposon system

The development of non-viral gene-transfer technologies that can support stable chromosomal integration and persistent gene expression in vivo is desirable. Here we describe the successful use of transposon technology for the nonhomologous insertion of foreign genes into the genomes of adult mammals using naked DNA. We show that the Sleeping Beauty transposase can efficiently insert transposon DNA into the mouse genome in approximately 5-6% of transfected mouse liver cells. Chromosomal transposition resulted in long-term expression (>5 months) of human blood coagulation factor IX at levels that were therapeutic in a mouse model of haemophilia B. Our results establish DNA-mediated transposition as a new genetic tool for mammals, and provide new strategies to improve existing non-viral and viral vectors for human gene therapy applications.     

CpG methylation is maintained in human cancer cells lacking DNMT1

Hypermethylation is associated with the silencing of tumour susceptibility genes in several forms of cancer; however, the mechanisms responsible for this aberrant methylation are poorly understood. The prototypic DNA methyltransferase, DNMT1, has been widely assumed to be responsible for most of the methylation of the human genome, including the abnormal methylation found in cancers. To test this hypothesis, we disrupted the DNMT1 gene through homologous recombination in human colorectal carcinoma cells. Here we show that cells lacking DNMT1 exhibited markedly decreased cellular DNA methyltransferase activity, but there was only a 20% decrease in overall genomic methylation. Although juxtacentromeric satellites became significantly demethylated, most of the loci that we analysed, including the tumour suppressor gene p16INK4a, remained fully methylated and silenced. These results indicate that DNMT1 has an unsuspected degree of regional specificity in human cells and that methylating activities other than DNMT1 can maintain the methylation of most of the genome.     

丰富的自然资源与宏伟的开拓前景——论海南省的开发战略

海南岛是我国第二大岛,资源丰富,在党的十一届三中全会以来,发展很快.现在国家把海南岛建成海南省,对它实行比其他经济特区更特殊、更开放、更优惠、更灵活的政策,将成为我国最开放的省和最大的经济特区。使富饶转化为富裕、内向转化为外向,在国际大循环中加快经济的发展.     

Lipolytic response of ‘diabetic’ mice (db/db) to isoproterenol and propranolol in vivo

Summary The genetically diabetic and obesedb/db mice responded lipolytically to isoproterenol and propranolol similarly to normal mice in vivo. However, considering the large amount of triglyceride in adb/db mouse, we conclude that the in vivo response ofdb/db adipose tissue is deficient in magnitude.     

CENP-E is a putative kinetochore motor that accumulates just before mitosis.

The mechanics of chromosome movement, mitotic spindle assembly and spindle elongation have long been central questions of cell biology. After attachment in prometaphase of a microtubule from one pole, duplicated chromosome pairs travel towards the pole in a rapid but discontinuous motion. This is followed by a slower congression towards the midplate as the chromosome pair orients with each kinetochore attached to the microtubules from the nearest pole. The pairs disjoin at anaphase and translocate to opposite poles and the interpolar distance increases. Here we identify CENP-E as a kinesin-like motor protein (M(r) 312,000) that accumulates in the G2 phase of the cell cycle. CENP-E associates with kinetochores during congression, relocates to the spindle midzone at anaphase, and is quantitatively discarded at the end of the cell division. CENP-E is likely to be one of the motors responsible for mammalian chromosome movement and/or spindle elongation.