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101.
Mycorrhizal weathering of apatite as an important calcium source in base-poor forest ecosystems 总被引:15,自引:0,他引:15
Blum JD Klaue A Nezat CA Driscoll CT Johnson CE Siccama TG Eagar C Fahey TJ Likens GE 《Nature》2002,417(6890):729-731
The depletion of calcium in forest ecosystems of the northeastern USA is thought to be a consequence of acidic deposition and to be at present restricting the recovery of forest and aquatic systems now that acidic deposition itself is declining. This depletion of calcium has been inferred from studies showing that sources of calcium in forest ecosystems namely, atmospheric deposition and mineral weathering of silicate rocks such as plagioclase, a calcium-sodium silicate do not match calcium outputs observed in forest streams. It is therefore thought that calcium is being lost from exchangeable and organically bound calcium in forest soils. Here we investigate the sources of calcium in the Hubbard Brook experimental forest, through analysis of calcium and strontium abundances and strontium isotope ratios within various soil, vegetation and hydrological pools. We show that the dissolution of apatite (calcium phosphate) represents a source of calcium that is comparable in size to known inputs from atmospheric sources and silicate weathering. Moreover, apatite-derived calcium was utilized largely by ectomycorrhizal tree species, suggesting that mycorrhizae may weather apatite and absorb the released ions directly, without the ions entering the exchangeable soil pool. Therefore, it seems that apatite weathering can compensate for some of the calcium lost from base-poor ecosystems, and should be considered when estimating soil acidification impacts and calcium cycling. 相似文献
102.
103.
R. Joel Rahn 《上海理工大学学报》1988,(1)
In previous work, the analysis of the effects of aggregating simple dynamic systems has been studied by applying methods developed for thermodynamic systems in order to take account of stochastic effects. This approach is based on the Master Equation for the probability density of the contents of a vector of system levels. The goal of these studies is to determine the dynamic characteristics of systems composed of a population of sub-systems with the same dynamic structure while accounting for novel behavior that is introduced by the process of aggregating the sub-systems into the larger system. 相似文献
104.
Selective killing of HIV-infected cells by recombinant human CD4-Pseudomonas exotoxin hybrid protein 总被引:40,自引:0,他引:40
V K Chaudhary T Mizukami T R Fuerst D J FitzGerald B Moss I Pastan E A Berger 《Nature》1988,335(6188):369-372
It is projected that in the absence of effective therapy, most individuals infected with human immunodeficiency virus (HIV) will develop acquired immune deficiency syndrome (AIDS) and ultimately succumb to a combination of opportunistic microbial infections, malignancies and direct pathogenic effects of the virus. Anti-viral agents, immunomodulators, and inhibitors of specific HIV functions are being tested as potential treatments to alleviate the high morbidity and mortality. An alternative therapeutic concept involves the development of cytotoxic agents that are targeted to kill HIV-infected cells. Here we describe the purification and characterization of a recombinant protein produced in Escherichia coli that contains the HIV-binding portion of the human CD4 molecule linked to active regions of Pseudomonas exotoxin A. This hybrid protein displays selective toxicity toward cells expressing the HIV envelope glycoprotein and thus represents a promising novel therapeutic agent for the treatment of AIDS. 相似文献
105.
106.
The DNA sequence and comparative analysis of human chromosome 5 总被引:1,自引:0,他引:1
Schmutz J Martin J Terry A Couronne O Grimwood J Lowry S Gordon LA Scott D Xie G Huang W Hellsten U Tran-Gyamfi M She X Prabhakar S Aerts A Altherr M Bajorek E Black S Branscomb E Caoile C Challacombe JF Chan YM Denys M Detter JC Escobar J Flowers D Fotopulos D Glavina T Gomez M Gonzales E Goodstein D Grigoriev I Groza M Hammon N Hawkins T Haydu L Israni S Jett J Kadner K Kimball H Kobayashi A Lopez F Lou Y Martinez D Medina C Morgan J Nandkeshwar R Noonan JP Pitluck S Pollard M Predki P 《Nature》2004,431(7006):268-274
Chromosome 5 is one of the largest human chromosomes and contains numerous intrachromosomal duplications, yet it has one of the lowest gene densities. This is partially explained by numerous gene-poor regions that display a remarkable degree of noncoding conservation with non-mammalian vertebrates, suggesting that they are functionally constrained. In total, we compiled 177.7 million base pairs of highly accurate finished sequence containing 923 manually curated protein-coding genes including the protocadherin and interleukin gene families. We also completely sequenced versions of the large chromosome-5-specific internal duplications. These duplications are very recent evolutionary events and probably have a mechanistic role in human physiological variation, as deletions in these regions are the cause of debilitating disorders including spinal muscular atrophy. 相似文献
107.
Orosz JA McClintock JE Narayan R Bailyn CD Hartman JD Macri L Liu J Pietsch W Remillard RA Shporer A Mazeh T 《Nature》2007,449(7164):872-875
Stellar-mass black holes are found in X-ray-emitting binary systems, where their mass can be determined from the dynamics of their companion stars. Models of stellar evolution have difficulty producing black holes in close binaries with masses more than ten times that of the Sun (>10; ref. 4), which is consistent with the fact that the most massive stellar black holes known so far all have masses within one standard deviation of 10. Here we report a mass of (15.65 +/- 1.45) for the black hole in the recently discovered system M 33 X-7, which is located in the nearby galaxy Messier 33 (M 33) and is the only known black hole that is in an eclipsing binary. To produce such a massive black hole, the progenitor star must have retained much of its outer envelope until after helium fusion in the core was completed. On the other hand, in order for the black hole to be in its present 3.45-day orbit about its (70.0 +/- 6.9) companion, there must have been a 'common envelope' phase of evolution in which a significant amount of mass was lost from the system. We find that the common envelope phase could not have occurred in M 33 X-7 unless the amount of mass lost from the progenitor during its evolution was an order of magnitude less than what is usually assumed in evolutionary models of massive stars. 相似文献
108.
de Bakker PI Burtt NP Graham RR Guiducci C Yelensky R Drake JA Bersaglieri T Penney KL Butler J Young S Onofrio RC Lyon HN Stram DO Haiman CA Freedman ML Zhu X Cooper R Groop L Kolonel LN Henderson BE Daly MJ Hirschhorn JN Altshuler D 《Nature genetics》2006,38(11):1298-1303
A general question for linkage disequilibrium-based association studies is how power to detect an association is compromised when tag SNPs are chosen from data in one population sample and then deployed in another sample. Specifically, it is important to know how well tags picked from the HapMap DNA samples capture the variation in other samples. To address this, we collected dense data uniformly across the four HapMap population samples and eleven other population samples. We picked tag SNPs using genotype data we collected in the HapMap samples and then evaluated the effective coverage of these tags in comparison to the entire set of common variants observed in the other samples. We simulated case-control association studies in the non-HapMap samples under a disease model of modest risk, and we observed little loss in power. These results demonstrate that the HapMap DNA samples can be used to select tags for genome-wide association studies in many samples around the world. 相似文献
109.
Arking DE Pfeufer A Post W Kao WH Newton-Cheh C Ikeda M West K Kashuk C Akyol M Perz S Jalilzadeh S Illig T Gieger C Guo CY Larson MG Wichmann HE Marbán E O'Donnell CJ Hirschhorn JN Kääb S Spooner PM Meitinger T Chakravarti A 《Nature genetics》2006,38(6):644-651
Extremes of the electrocardiographic QT interval, a measure of cardiac repolarization, are associated with increased cardiovascular mortality. We identified a common genetic variant influencing this quantitative trait through a genome-wide association study on 200 subjects at the extremes of a population-based QT interval distribution of 3,966 subjects from the KORA cohort in Germany, with follow-up screening of selected markers in the remainder of the cohort. We validated statistically significant findings in two independent samples of 2,646 subjects from Germany and 1,805 subjects from the US Framingham Heart Study. This genome-wide study identified NOS1AP (CAPON), a regulator of neuronal nitric oxide synthase, as a new target that modulates cardiac repolarization. Approximately 60% of subjects of European ancestry carry at least one minor allele of the NOS1AP genetic variant, which explains up to 1.5% of QT interval variation. 相似文献
110.
Homozygous mutation of AURKC yields large-headed polyploid spermatozoa and causes male infertility 总被引:1,自引:0,他引:1
Dieterich K Soto Rifo R Faure AK Hennebicq S Ben Amar B Zahi M Perrin J Martinez D Sèle B Jouk PS Ohlmann T Rousseaux S Lunardi J Ray PF 《Nature genetics》2007,39(5):661-665
The World Health Organization conservatively estimates that 80 million people suffer from infertility worldwide. Male factors are believed to be responsible for 20-50% of all infertility cases, but microdeletions of the Y chromosome are the only genetic defects altering human spermatogenesis that have been reported repeatedly. We focused our work on infertile men with a normal somatic karyotype but typical spermatozoa mainly characterized by large heads, a variable number of tails and an increased chromosomal content (OMIM 243060). We performed a genome-wide microsatellite scan on ten infertile men presenting this characteristic phenotype. In all of these men, we identified a common region of homozygosity harboring the aurora kinase C gene (AURKC) with a single nucleotide deletion in the AURKC coding sequence. In addition, we show that this founder mutation results in premature termination of translation, yielding a truncated protein that lacks the kinase domain. We conclude that the absence of AURKC causes male infertility owing to the production of large-headed multiflagellar polyploid spermatozoa. 相似文献