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991.
The habitat and nature of early life 总被引:21,自引:0,他引:21
Earth is over 4,500 million years old. Massive bombardment of the planet took place for the first 500-700 million years, and the largest impacts would have been capable of sterilizing the planet. Probably until 4,000 million years ago or later, occasional impacts might have heated the ocean over 100 degrees C. Life on Earth dates from before about 3,800 million years ago, and is likely to have gone through one or more hot-ocean 'bottlenecks'. Only hyperthermophiles (organisms optimally living in water at 80-110 degrees C) would have survived. It is possible that early life diversified near hydrothermal vents, but hypotheses that life first occupied other pre-bottleneck habitats are tenable (including transfer from Mars on ejecta from impacts there). Early hyperthermophile life, probably near hydrothermal systems, may have been non-photosynthetic, and many housekeeping proteins and biochemical processes may have an original hydrothermal heritage. The development of anoxygenic and then oxygenic photosynthesis would have allowed life to escape the hydrothermal setting. By about 3,500 million years ago, most of the principal biochemical pathways that sustain the modern biosphere had evolved, and were global in scope. 相似文献
992.
Involvement of chemokine receptors in breast cancer metastasis 总被引:344,自引:0,他引:344
Müller A Homey B Soto H Ge N Catron D Buchanan ME McClanahan T Murphy E Yuan W Wagner SN Barrera JL Mohar A Verástegui E Zlotnik A 《Nature》2001,410(6824):50-56
Breast cancer is characterized by a distinct metastatic pattern involving the regional lymph nodes, bone marrow, lung and liver. Tumour cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokines and their receptors. Here we report that the chemokine receptors CXCR4 and CCR7 are highly expressed in human breast cancer cells, malignant breast tumours and metastases. Their respective ligands CXCL12/SDF-1alpha and CCL21/6Ckine exhibit peak levels of expression in organs representing the first destinations of breast cancer metastasis. In breast cancer cells, signalling through CXCR4 or CCR7 mediates actin polymerization and pseudopodia formation, and subsequently induces chemotactic and invasive responses. In vivo, neutralizing the interactions of CXCL12/CXCR4 significantly impairs metastasis of breast cancer cells to regional lymph nodes and lung. Malignant melanoma, which has a similar metastatic pattern as breast cancer but also a high incidence of skin metastases, shows high expression levels of CCR10 in addition to CXCR4 and CCR7. Our findings indicate that chemokines and their receptors have a critical role in determining the metastatic destination of tumour cells. 相似文献
993.
Synaesthesia is an unusual perceptual phenomenon in which events in one sensory modality induce vivid sensations in another. Individuals may 'taste' shapes, 'hear' colours, or 'feel' sounds. Synaesthesia was first described over a century ago, but little is known about its underlying causes or its effects on cognition. Most reports have been anecdotal or have focused on isolated unusual cases. Here we report an investigation of 15 individuals with colour-graphemic synaesthesia, each of whom experiences idiosyncratic but highly consistent colours for letters and digits. Using a colour-form interference paradigm, we show that induced synaesthetic experiences cannot be consciously suppressed even when detrimental to task performance. In contrast, if letters and digits are presented briefly and masked, so that they are processed but unavailable for overt report, the synaesthesia is eliminated. These results show that synaesthetic experiences can be prevented despite substantial processing of the sensory stimuli that otherwise trigger them. We conclude that automatic binding of colour and alphanumeric form in synaesthesia arises after initial processes of letter and digit recognition are complete. 相似文献
994.
The electrical resistance of a conductor is intimately related to the relaxation of the momentum of charge carriers. In a simple model, the accelerating force exerted on electrons by an applied electric field is balanced by a frictional force arising from their frequent collisions with obstacles such as impurities, grain boundaries or other deviations from a perfect crystalline order. Thus, in the absence of any scattering, the electrical resistance should vanish altogether. Here, we observe such vanishing four-terminal resistance in a single-mode ballistic quantum wire. This result contrasts the value of the standard two-probe resistance measurements of h/2e2 approximately 13 kOmega. The measurements are conducted in the highly controlled geometry afforded by epitaxial growth onto the cleaved edge of a high-quality GaAs/AlGaAs heterostructure. Two weakly invasive voltage probes are attached to the central section of a ballistic quantum wire to measure the inherent resistance of this clean one-dimensional conductor. 相似文献
995.
从我国发病的玉米材料中提取水稻黑条矮缩病毒,抽提病毒RNA,利用RT-PCR等手段,获得了病毒基因组第九组分(S9)cDNA克隆。序列分析结果表明:S9全长1900bp,含有2个不重叠的ORF,编码蛋白的分子质量分别为39.9,24.2ku,与日本株S9核苷酸序列同源性为89%,与意大利株MRDV S8同源性为86%。 相似文献
996.
N Matsunami B Smith L Ballard M W Lensch M Robertson H Albertsen C O Hanemann H W Müller T D Bird R White 《Nature genetics》1992,1(3):176-179
Charcot-Marie-Tooth disease 1A (CMT1A) is a hereditary demyelinating peripheral neuropathy, associated with a DNA duplication on chromosome 17p11.2. A related disorder in the mouse, trembler (Tr), maps to mouse chromosome 11 which has syntenic homology to human chromosome 17p. Recently, the peripheral myelin protein-22 (pmp-22) gene was identified as the likely Tr locus. We have constructed a partial yeast artificial chromosome contig spanning the CMT1A gene region and mapped the PMP-22 gene to the duplicated region. These observations further implicate PMP-22 as a candidate gene for CMT1A, and suggest that over-expression of this gene may be one mechanism that produces the CMT1A phenotype. 相似文献
997.
A radiation hybrid map of the rat genome containing 5,255 markers. 总被引:17,自引:0,他引:17
T K Watanabe M T Bihoreau L C McCarthy S L Kiguwa H Hishigaki A Tsuji J Browne Y Yamasaki A Mizoguchi-Miyakita K Oga T Ono S Okuno N Kanemoto E Takahashi K Tomita H Hayashi M Adachi C Webber M Davis S Kiel C Knights A Smith R Critcher J Miller T Thangarajah P J Day J R Hudson Y Irie T Takagi Y Nakamura P N Goodfellow G M Lathrop A Tanigami M R James 《Nature genetics》1999,22(1):27-36
A whole-genome radiation hybrid (RH) panel was used to construct a high-resolution map of the rat genome based on microsatellite and gene markers. These include 3,019 new microsatellite markers described here for the first time and 1,714 microsatellite markers with known genetic locations, allowing comparison and integration of maps from different sources. A robust RH framework map containing 1,030 positions ordered with odds of at least 1,000:1 has been defined as a tool for mapping these markers, and for future RH mapping in the rat. More than 500 genes which have been mapped in mouse and/or human were localized with respect to the rat RH framework, allowing the construction of detailed rat-mouse and rat-human comparative maps and illustrating the power of the RH approach for comparative mapping. 相似文献
998.
Dobbins SE Broderick P Melin B Feychting M Johansen C Andersson U Brännström T Schramm J Olver B Lloyd A Ma YP Hosking FJ Lönn S Ahlbom A Henriksson R Schoemaker MJ Hepworth SJ Hoffmann P Mühleisen TW Nöthen MM Moebus S Eisele L Kosteljanetz M Muir K Swerdlow A Simon M Houlston RS 《Nature genetics》2011,43(9):825-827
To identify susceptibility loci for meningioma, we conducted a genome-wide association study of 859 affected individuals (cases) and 704 controls with validation in two independent sample sets totaling 774 cases and 1,764 controls. We identified a new susceptibility locus for meningioma at 10p12.31 (MLLT10, rs11012732, odds ratio = 1.46, P(combined) = 1.88 × 10(-14)). This finding advances our understanding of the genetic basis of meningioma development. 相似文献
999.
Zusammenfassung In kombinierter histochemischer und biochemischer Untersuchung werden Dopamin-, Noradrenalin-und 5-Hydroxytryptamin-Neurone nach Entfernung von Cortex cerebri und Cerebellum studiert. Es ergibt sich, dass die Noradrenalin-Nerventerminale, welche Cortex cerebri und Cerebellum innervieren, vermutlich von feinen Axonen her stammen, deren Zellkörper mindestens zum Teil in der Formatio reticularis der Medulla oblongata gelegen sind. Die Noradrenalin-und 5-Hydroxytryptamin-Axone, die nach dem Cortex cerebri ziehen, passieren vermutlich zur Hauptsache das Cingulum. 相似文献
1000.
A new rapid micromethod for protein separation under a radial electric field is described. As many as 12 rabbit serum samples could be separated in 4--6 min. 相似文献