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11.
Marco G. Alves Luís Rato Rui A. Carvalho Paula I. Moreira Sílvia Socorro Pedro F. Oliveira 《Cellular and molecular life sciences : CMLS》2013,70(5):777-793
Hormonal regulation is essential to spermatogenesis. Sertoli cells (SCs) have functions that reach far beyond the physical support of germ cells, as they are responsible for creating the adequate ionic and metabolic environment for germ cell development. Thus, much attention has been given to the metabolic functioning of SCs. During spermatogenesis, germ cells are provided with suitable metabolic substrates, in a set of events mediated by SCs. Multiple signaling cascades regulate SC function and several of these signaling pathways are hormone-dependent and cell-specific. Within the seminiferous tubules, only SCs possess receptors for some hormones rendering them major targets for the hormonal signaling that regulates spermatogenesis. Although the mechanisms by which SCs fulfill their own and germ cells metabolic needs are mostly studied in vitro, SC metabolism is unquestionably a regulation point for germ cell development and the hormonal control of these processes is required for a normal spermatogenesis. 相似文献
12.
Haigis KM Kendall KR Wang Y Cheung A Haigis MC Glickman JN Niwa-Kawakita M Sweet-Cordero A Sebolt-Leopold J Shannon KM Settleman J Giovannini M Jacks T 《Nature genetics》2008,40(5):600-608
Kras is commonly mutated in colon cancers, but mutations in Nras are rare. We have used genetically engineered mice to determine whether and how these related oncogenes regulate homeostasis and tumorigenesis in the colon. Expression of K-Ras(G12D) in the colonic epithelium stimulated hyperproliferation in a Mek-dependent manner. N-Ras(G12D) did not alter the growth properties of the epithelium, but was able to confer resistance to apoptosis. In the context of an Apc-mutant colonic tumor, activation of K-Ras led to defects in terminal differentiation and expansion of putative stem cells within the tumor epithelium. This K-Ras tumor phenotype was associated with attenuated signaling through the MAPK pathway, and human colon cancer cells expressing mutant K-Ras were hypersensitive to inhibition of Raf, but not Mek. These studies demonstrate clear phenotypic differences between mutant Kras and Nras, and suggest that the oncogenic phenotype of mutant K-Ras might be mediated by noncanonical signaling through Ras effector pathways. 相似文献
13.
A. di Marco F. Zunino P. Orezzi R. A. Gambetta 《Cellular and molecular life sciences : CMLS》1972,28(3):327-329
Riassunto Quale effetto dell'irradiazione UV è stato osservato un legame insolitamente forte tra daunomicina ed acidi nucleici, che suggerisce la possibilità della formazione di un legame covalente. 相似文献
14.
Résumé Les auteurs ont préparé avec une enzyme de la thiotaurine et de l'hypotaurine marquées par le et S35 ont démontré que ces deux composés peuvent échanger spontanément un atome de soufre en se transformant l'un dans l'autre. 相似文献
15.
Riassunto È stato dimostrato che la transulfurazione che consegue alla incubazione dei solfinati con zolfo ed un composto tiolico è dovuta in parte alla produzione di un polisolfuro organico, formato dal tiolo e zolfo, ed in parte al polisolfuro inorganico, formato dalla decomposizione di quello organico. L'entità della transulfurazione prodotta direttamente dal polisolfuro organico varia con il tipo di polisolfuro e dipende dalla sua stabilità nelle condizioni usate. 相似文献
16.
Release of chromatin protein HMGB1 by necrotic cells triggers inflammation 总被引:129,自引:0,他引:129
High mobility group 1 (HMGB1) protein is both a nuclear factor and a secreted protein. In the cell nucleus it acts as an architectural chromatin-binding factor that bends DNA and promotes protein assembly on specific DNA targets. Outside the cell, it binds with high affinity to RAGE (the receptor for advanced glycation end products) and is a potent mediator of inflammation. HMGB1 is secreted by activated monocytes and macrophages, and is passively released by necrotic or damaged cells. Here we report that Hmgb1(-/-) necrotic cells have a greatly reduced ability to promote inflammation, which proves that the release of HMGB1 can signal the demise of a cell to its neighbours. Apoptotic cells do not release HMGB1 even after undergoing secondary necrosis and partial autolysis, and thus fail to promote inflammation even if not cleared promptly by phagocytic cells. In apoptotic cells, HMGB1 is bound firmly to chromatin because of generalized underacetylation of histone and is released in the extracellular medium (promoting inflammation) if chromatin deacetylation is prevented. Thus, cells undergoing apoptosis are programmed to withhold the signal that is broadcast by cells that have been damaged or killed by trauma. 相似文献
17.
MicroRNAs (miRNAs) are produced by the Dicer1 enzyme; the role of Dicer1 in vertebrate development is unknown. Here we report target-selected inactivation of the dicer1 gene in zebrafish. We observed an initial build-up of miRNA levels, produced by maternal Dicer1, in homozygous dicer1 mutants, but miRNA accumulation stopped after a few days. This resulted in developmental arrest around day 10. These results indicate that miRNA-producing Dicer1 is essential for vertebrate development. 相似文献
18.
Bonatti E Ligi M Brunelli D Cipriani A Fabretti P Ferrante V Gasperini L Ottolini L 《Nature》2003,423(6939):499-505
A 20-Myr record of creation of oceanic lithosphere is exposed along a segment of the central Mid-Atlantic Ridge on an uplifted sliver of lithosphere. The degree of melting of the mantle that is upwelling below the ridge, estimated from the chemistry of the exposed mantle rocks, as well as crustal thickness inferred from gravity measurements, show oscillations of approximately 3-4 Myr superimposed on a longer-term steady increase with time. The time lag between oscillations of mantle melting and crustal thickness indicates that the mantle is upwelling at an average rate of approximately 25 mm x yr(-1), but this appears to vary through time. Slow-spreading lithosphere seems to form through dynamic pulses of mantle upwelling and melting, leading not only to along-axis segmentation but also to across-axis structural variability. Also, the central Mid-Atlantic Ridge appears to have become steadily hotter over the past 20 Myr, possibly owing to north-south mantle flow. 相似文献
19.
Recent financial research has provided evidence on the predictability of asset returns. In this paper we consider the results contained in Pesaran and Timmerman (1995), which provided evidence on predictability of excess returns in the US stock market over the sample 1959–1992. We show that the extension of the sample to the nineties weakens considerably the statistical and economic significance of the predictability of stock returns based on earlier data. We propose an extension of their framework, based on the explicit consideration of model uncertainty under rich parameterizations for the predictive models. We propose a novel methodology to deal with model uncertainty based on ‘thick’ modelling, i.e. on considering a multiplicity of predictive models rather than a single predictive model. We show that portfolio allocations based on a thick modelling strategy systematically outperform thin modelling. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
20.
本书介绍了意大利比萨大学一个团队的开发项目——CDMA移动终端接受器.以及从中获取的经验,为通信理论到VLSI实现建立了一座桥梁,呈现了从最初系统设计到最终硬件测试所需要的电信和电子相关知识,主要目的是为通信电路的设计提供理论和实践上的支持。书中介绍的知识和技术可以运用到更一般的无线调制解调器的构架设计和实现。 相似文献