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291.
Selenium is critical in livestock nutrition; forage can be either potentially deficient or toxic in this element. Selenium is accumulated in excessive amounts by a relatively few species of plants. Several of these plants, termed indicator species, occur in the western Great Basin; however, selenium toxicity is not a problem in Nevada for domestic livestock. The detection of marginal dietary deficiencies of selenium is of much greater economic importance to the livestock industry than an excess of this element. Selenium occurs as a trace element in the composition of various minerals. Selenium levels are very low in volcanic rocks of recent origin. Accumulations of this element require concentration through secondary dispersion and subsequent sedimentation. Therefore, excesses of selenium are usually associated with siltstone, sandstone, or other sedimentary rocks. Selenium is usually found in soils as selenate, a water-soluble mineral. The selenium concentration of plants is directly related to the selenate concentration in soil. In soils low in selenate, the ability of plants to accumulate selenium is similar. In soils with high levels of selenate, indicator species accumulate 10 times as much selenium as other species. The foliage of most indicator plants is generally avoided by grazing animals. Deficiencies in dietary selenium are associated with the occurrence of white muscle disease, retained placentas, and general unthriftiness of animals. Insufficient dietary selenium can be overcome through injection, intraluminal pellets, or supplementation with salt mixtures. 相似文献
292.
Andrew J. Quantock Robert D. Young Tomoya O. Akama 《Cellular and molecular life sciences : CMLS》2010,67(6):891-906
Keratan sulphate (KS) is the predominant glycosaminoglycan (GAG) in the cornea of the eye, where it exists in proteoglycan
(PG) form. KS-PGs have long been thought to play a pivotal role in the establishment and maintenance of the array of regularly-spaced
and uniformly-thin collagen fibrils which make up the corneal stroma. This characteristic arrangement of fibrils allows light
to pass through the cornea. Indeed, perturbations to the synthesis of KS-PG core proteins in genetically altered mice lead
to structural matrix alterations and corneal opacification. Similarly, mutations in enzymes responsible for the sulphation
of KS-GAG chains are causative for the inherited human disease, macular corneal dystrophy, which is manifested clinically
by progressive corneal cloudiness starting in young adulthood. 相似文献
293.
Keshet I Schlesinger Y Farkash S Rand E Hecht M Segal E Pikarski E Young RA Niveleau A Cedar H Simon I 《Nature genetics》2006,38(2):149-153
DNA methylation has a role in the regulation of gene expression during normal mammalian development but can also mediate epigenetic silencing of CpG island genes in cancer and other diseases. Many individual genes (including tumor suppressors) have been shown to undergo de novo methylation in specific tumor types, but the biological logic inherent in this process is not understood. To decipher this mechanism, we have adopted a new approach for detecting CpG island DNA methylation that can be used together with microarray technology. Genome-wide analysis by this technique demonstrated that tumor-specific methylated genes belong to distinct functional categories, have common sequence motifs in their promoters and are found in clusters on chromosomes. In addition, many are already repressed in normal cells. These results are consistent with the hypothesis that cancer-related de novo methylation may come about through an instructive mechanism. 相似文献
294.
295.
Kato N Takeuchi F Tabara Y Kelly TN Go MJ Sim X Tay WT Chen CH Zhang Y Yamamoto K Katsuya T Yokota M Kim YJ Ong RT Nabika T Gu D Chang LC Kokubo Y Huang W Ohnaka K Yamori Y Nakashima E Jaquish CE Lee JY Seielstad M Isono M Hixson JE Chen YT Miki T Zhou X Sugiyama T Jeon JP Liu JJ Takayanagi R Kim SS Aung T Sung YJ Zhang X Wong TY Han BG Kobayashi S Ogihara T Zhu D Iwai N Wu JY Teo YY Tai ES Cho YS He J 《Nature genetics》2011,43(6):531-538
We conducted a meta-analysis of genome-wide association studies of systolic (SBP) and diastolic (DBP) blood pressure in 19,608 subjects of east Asian ancestry from the AGEN-BP consortium followed up with de novo genotyping (n = 10,518) and further replication (n = 20,247) in east Asian samples. We identified genome-wide significant (P < 5 × 10(-8)) associations with SBP or DBP, which included variants at four new loci (ST7L-CAPZA1, FIGN-GRB14, ENPEP and NPR3) and a newly discovered variant near TBX3. Among the five newly discovered variants, we obtained significant replication in the independent samples for all of these loci except NPR3. We also confirmed seven loci previously identified in populations of European descent. Moreover, at 12q24.13 near ALDH2, we observed strong association signals (P = 7.9 × 10(-31) and P = 1.3 × 10(-35) for SBP and DBP, respectively) with ethnic specificity. These findings provide new insights into blood pressure regulation and potential targets for intervention. 相似文献
296.
This paper describes in detail a flexible approach to nonstationary time series analysis based on a Dynamic Harmonic Regression (DHR) model of the Unobserved Components (UC) type, formulated within a stochastic state space setting. The model is particularly useful for adaptive seasonal adjustment, signal extraction and interpolation over gaps, as well as forecasting or backcasting. The Kalman Filter and Fixed Interval Smoothing algorithms are exploited for estimating the various components, with the Noise Variance Ratio and other hyperparameters in the stochastic state space model estimated by a novel optimization method in the frequency domain. Unlike other approaches of this general type, which normally exploit Maximum Likelihood methods, this optimization procedure is based on a cost function defined in terms of the difference between the logarithmic pseudo‐spectrum of the DHR model and the logarithmic autoregressive spectrum of the time series. The cost function not only seems to yield improved convergence characteristics when compared with the alternative ML cost function, but it also has much reduced numerical requirements. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
297.
Eunah Kim Joon Hyun Kim Keunhee Seo Ka Young Hong Seon Woo A. An Junyoung Kwon Seung-Jae V. Lee Sung Key Jang 《Cellular and molecular life sciences : CMLS》2018,75(23):4287-4300
The initiator tRNA (Met-tRNA i Met ) at the P site of the small ribosomal subunit plays an important role in the recognition of an mRNA start codon. In bacteria, the initiator tRNA carrier, IF2, facilitates the positioning of Met-tRNA i Met on the small ribosomal subunit. Eukarya contain the Met-tRNA i Met carrier, eIF2 (unrelated to IF2), whose carrier activity is inhibited under stress conditions by the phosphorylation of its α-subunit by stress-activated eIF2α kinases. The stress-resistant initiator tRNA carrier, eIF2A, was recently uncovered and shown to load Met-tRNA i Met on the 40S ribosomal subunit associated with a stress-resistant mRNA under stress conditions. Here, we report that eIF2A interacts and functionally cooperates with eIF5B (a homolog of IF2), and we describe the functional domains of eIF2A that are required for its binding of Met-tRNA i Met , eIF5B, and a stress-resistant mRNA. The results indicate that the eukaryotic eIF5B–eIF2A complex functionally mimics the bacterial IF2 containing ribosome-, GTP-, and initiator tRNA-binding domains in a single polypeptide. 相似文献
298.
New hypothesis of insulin secretion 总被引:77,自引:0,他引:77
299.
Molecular cloning of cDNA for murine interleukin-3 总被引:51,自引:0,他引:51
M C Fung A J Hapel S Ymer D R Cohen R M Johnson H D Campbell I G Young 《Nature》1984,307(5948):233-237
The cDNA sequence for murine interleukin-3, one of the colony stimulating factors that regulate haematopoiesis, codes for a polypeptide of 166 amino acids including a putative signal peptide. The predicted amino acid sequence indicates that formation of mature interleukin-3 involves proteolytic removal of not only the signal peptide but additional amino-terminal amino acids. 相似文献
300.
Martin R. Young 《Journal of forecasting》1996,15(5):355-367
Akaike's BAYSEA approach to seasonal decomposition is designed to capture the respective merits of several pre-existing adjustment techniques. BAYSEA is computationally efficient, requires only weak assumptions about the data-generating process, and is based on solid inferential (namely, Bayesian) foundations. We present a model similar to that used in BAYSEA, but based on a double exponential rather than a Gaussian error model. The resulting procedure has the advantages of Akaike's method, but in addition is resistant to outliers. The optimal decomposition is obtained rapidly using a sparse linear programming code. Confidence bands and predictive intervals can be obtained using Gibbs sampling. 相似文献