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991.
The replicative lifespan of normal somatic cells is restricted by the erosion of telomeres, which are protective caps at the
ends of linear chromosomes. The loss of telomeres induces antiproliferative signals that eventually lead to cellular senescence.
The enzyme complex telomerase can maintain telomeres, but its expression is confined to highly proliferative cells such as
stem cells and tumor cells. The immense regenerative capacity of the hematopoietic system is provided by a distinct type of
adult stem cell: hematopoietic stem cells (HSCs). Although blood cells have to be produced continuously throughout life, the
HSC pool seems not to be spared by aging processes. Indeed, limited expression of telomerase is not sufficient to prevent
telomere shortening in these cells, which is thought ultimately to limit their proliferative capacity. In this review, we
discuss the relevance of telomere maintenance for the hematopoietic stem cell compartment and consider potential functions
of telomerase in this context. We also present possible clinical applications of telomere manipulation in HSCs and new insights
affecting the aging of the hematopoietic stem cell pool and replicative exhaustion.
This work was supported by European Community Grant LSHC-CT-2004-502943 (MOL CANCER MED). 相似文献
992.
Chi Zhang Hanqin Tian Shufen Pan Mingliang Liu Graeme Lockaby Erik B. Schilling John Stanturf 《Ecosystems》2008,11(8):1211-1222
Forest regrowth after cropland abandonment and urban sprawl are two counteracting processes that have influenced carbon (C)
sequestration in the southeastern United States in recent decades. In this study, we examined patterns of land-use/land-cover
change and their effect on ecosystem C storage in three west Georgia counties (Muscogee, Harris, and Meriwether) that form
a rural–urban gradient. Using time series Landsat imagery data including MSS for 1974, TM for 1983 and 1991, and ETM for 2002,
we estimate that from 1974 to 2002, urban land use in the area has increased more than 380% (that is, 184 km2). Most newly urbanized land (63%) has been converted from forestland. Conversely, cropland and pasture area has decreased
by over 59% (that is, 380 km2). Most of the cropland area was converted to forest. As a result, the net change in forest area was small over the past 29
years. Based on Landsat imagery and agricultural census records, we reconstructed an annual gridded data set of land-cover
change for the three counties for the period 1850 to 2002. These data sets were then used as input to the Terrestrial Ecosystem
Model (TEM) to simulate land-use effects on C fluxes and storage for the study area. Simulated results suggest that C uptake
by forest regrowth (approximately 23.0 g C m−2 y−1) was slightly greater than the amount of C released due to deforestation (approximately 18.4 g C m−2 y−1), thus making the three counties a weak C sink. However, the relative importance of different deforestation processes in
this area changed significantly through time. Although agricultural deforestation was generally the most important C-release
process, the amount of C release attributable to urbanization has increased over time. Since 1990, urbanization has accounted
for 29% of total C loss from the study area. We conclude that balancing urban development and forest protection is critically
important for C management and policy making in the southeastern United States. 相似文献
993.
Mohd Zeeshan Ansari Jyoti Sharma Rajesh S Gokhale Debasisa Mohanty 《BMC bioinformatics》2008,9(1):454
Background
Secondary metabolites biosynthesized by polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) family of enzymes constitute several classes of therapeutically important natural products like erythromycin, rapamycin, cyclosporine etc. In view of their relevance for natural product based drug discovery, identification of novel secondary metabolite natural products by genome mining has been an area of active research. A number of different tailoring enzymes catalyze a variety of chemical modifications to the polyketide or nonribosomal peptide backbone of these secondary metabolites to enhance their structural diversity. Therefore, development of powerful bioinformatics methods for identification of these tailoring enzymes and assignment of their substrate specificity is crucial for deciphering novel secondary metabolites by genome mining. 相似文献994.
The production of recombinant proteins in plants is an active area of research and many different high-value proteins have
now been produced in plants. Tobacco leaves have many advantages for recombinant protein production particularly since they
allow field production without seeds, flowers or pollen and therefore provide for contained production. Despite these biosafety
advantages recombinant protein accumulation in leaves still needs to be improved. Elastin-like polypeptides are repeats of
the amino acids “VPGXG” that undergo a temperature dependant phase transition and have utility in the purification of recombinant
proteins but can also enhance the accumulation of recombinant proteins they are fused to. We have used a 11.3 kDa elastin-like
polypeptide as a fusion partner for three different target proteins, human interleukin-10, murine interleukin-4 and the native
major ampullate spidroin protein 2 gene from the spider Nephila clavipes. In both transient analyses and stable transformants the concentrations of the fusion proteins were at least an order of
magnitude higher for all of the fusion proteins when compared to the target protein alone. Therefore, fusions with a small
ELP tag can be used to significantly enhance the accumulation of a range of different recombinant proteins in plant leaves.
An erratum to this article can be found at 相似文献
995.
Factors influencing the spatial distribution of forest plant species in hedgerows of North-western Germany 总被引:2,自引:0,他引:2
In North-western Germany woodland fragmentation has caused a decline in many forest plant species. Hedgerows partly offer
a similar environment as forests and have been identified as potential habitats for forest plants in various studies from
North America and Western Europe. The objective of this study was to examine whether this applies also to Central Europe and
which variables affect the spatial distribution and abundance of forest plant species in hedgerows on a local scale. Three
hedgerow networks north of the city of Bremen, Germany, were selected as study areas and divided into totally 515 hedgerow
segments. In each segment we recorded all vascular plants and a large number of explanatory variables relating to structure,
spatial configuration, environment and management. Averaged across species there was a predominant effect of environmental
factors on the occurrence of forest species in the hedgerows, followed by spatial configuration and management. Hedgerow structure
was found to be less important. In general, forest species were favored by low nutrient and light availability as well as
high connectivity with other hedgerows or forest; they avoided hedgerows with a west-easterly orientation and an adjacent
land use in the form of fields or grasslands. Forest species found and not found in hedgerows did not differ in their environmental
preferences or life history traits. The number of threatened forest species in the hedgerows, however, was lower than expected
with respect to their overall proportion to the total number of forest species in the region. 相似文献
996.
João Marcelo Alvarenga Braga 《Kew Bulletin》2008,63(2):309-314
Summary
Calathea dryadica and Calathea reginae are described, circumscribed and illustrated. These new species are probably endemic to the Atlantic Forest of Rio de Janeiro
State in Southeast Brazil and are considered critically endangered because of the restricted geographic area of occurrence,
sometimes enclosed by densely urbanised areas. 相似文献
997.
998.
Sher Hayat Khan Deming Zhao Syed Zahid Ali Shah Mohammad Farooque Hassan Ting Zhu Zhiqi Song Xiangmei Zhou Lifeng Yang 《Cellular and molecular neurobiology》2017,37(4):717-728
Transmissible spongiform encephalopathies (TSEs) are caused by the accumulation of the abnormal prion protein scrapie (PrPSc). Prion protein aggregation, misfolding, and cytotoxicity in the brain are the major causes of neuronal dysfunction and ultimate neurodegeneration in all TSEs. Parkin, an E3 ubiquitin ligase, has been studied extensively in all major protein misfolding aggregating diseases, especially Parkinson’s disease and Alzheimer’s disease, but the role of parkin in TSEs remains unknown. Here we investigated the role of parkin in a prion disease cell model in which neuroblastoma2a (N2a) cells were treated with prion peptide PrP106–126. We observed a gradual decrease in the soluble parkin level upon treatment with PrP106–126 in a time-dependent manner. Furthermore, endogenous parkin colocalized with FITC-tagged prion fragment106–126. Overexpression of parkin in N2a cells via transfection repressed apoptosis by enhancing autophagy. Parkin-overexpressing cells also showed reductions in apoptotic BAX translocation to the mitochondria and cytochrome c release to the cytosol, which ultimately inhibited activation of proapoptotic caspases. Taken together, our findings reveal a parkin-mediated cytoprotective mechanism against PrP106–126 toxicity, which is a novel potential therapeutic target for treating prion diseases. 相似文献
999.
Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi,
especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on
the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous
forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production
of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching
data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty
acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2ω6,9 was used as an indicator to estimate
the total fungal biomass. Higher N deposition (20 kg N ha−1 y−1 compared with 10 kg N ha−1 y−1) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the
PLFA 16:1ω5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively
correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1ω9, a17:0 and 18:1ω7, while
some were negatively affected by pH, such as i15:0, 16:1ω7t, 10Me17:0 and cy19:0. In addition, N deposition had an effect
on the PLFAs 16:1ω7c and 16:1ω9 (negatively) and cy19:0 (positively). The production of EM mycelia is probably more sensitive
to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2ω6,9. Low amounts of EM mycelia covaried
with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at
increased N input. 相似文献
1000.
从红茶菌液中筛选获得一株产细菌纤维素的菌株BC-41,经生理生化分析和分子生物学鉴定,现证实该菌株为中间葡糖酸醋杆菌(Gluconacetobacter intermedius)。对该菌株所产生的细菌纤维素进行了物理特性的表征和分析,获得以下数据:BC-41所产的纤维素纯度达到91.32%,湿纤维素膜含水率达99.16%,每克干纤维素膜能吸水28.59 g;扫描电子显微镜观察,显示该纤维素具有网状结构,且纤维束宽度分布在40-100 nm之间;X射线衍射分析,证实该纤维素的晶型为纤维素I型,结晶指数为48.8%;通过黏度测定法,得出该纤维素的平均聚合度达2 100。 相似文献