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251.
Laura Riboni Hortensia D'Albora Emilia Carlevaro R. Dominguez 《Cellular and molecular life sciences : CMLS》1969,25(7):754-755
Résumé Des greffons d'ovaire de rat impubère placés dans la chambre antérieure de l'il du mâle castré, après traitement avec 0,5 mg de dipropionate d'stradiol ou avec deux doses de 1 mg de progestérone, ont montré une évidente ovulation. On interprète ce fait comme dû á l'action des hormones injectées dans le système nerveux central et qui favorisent le mécanisme de l'ovulation. 相似文献
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The sensing mechanisms of chemotactic bacteria allow them to respond sensitively to stimuli. Escherichia coli, for example, respond to changes in chemoattractant concentration of less than 10% over a range spanning six orders of magnitude. Sensitivity over this range depends on a nonlinear relationship between ligand concentration and output response. At low ligand concentrations, substantial amplification of the chemotactic signal is required; however, the mechanism responsible for this amplification remains unclear. Here we demonstrate that inter-receptor communication within a lattice acts to amplify and integrate sensory information. Synthetic multivalent ligands that interact through the low-abundance, galactose-sensing receptor Trg stabilize large clusters of chemoreceptors and markedly enhance signal output from these enforced clusters. On treatment with multivalent ligands, the response to the attractant serine is amplified by at least 100-fold. This amplification requires a full complement of chemoreceptors; deletion of the aspartate (Tar) or dipeptide (Tap) receptors diminishes the amplification of the serine response. These results demonstrate that the entire array is involved in sensing. This mode of information exchange has general implications for the processing of signals by cellular receptors. 相似文献
254.
Laura Foá-Tomasi F. Costanzo Gabriella Campadelli-Fiume 《Cellular and molecular life sciences : CMLS》1976,32(1):45-46
Summary The inhibition of RNA synthesis by -amanitin on vitro cultured cells is very slow. The action of various analogues of the toxin was tested and some of them proved more effective. Moreover pretreatment of cell cultures with DEAE-dextran greatly enhanced the effect of -amanitin.Acknowledgments. We thank ProfessorTh. Wieland and Dr.H. Faulstich (Max-Planck-Institut, Heidelberg) for the generous gift of amanitins. This investigation was supported by grant No. 74.00637.65 from C.N.R. (Roma). 相似文献
255.
Summary The locomotor activity of ovariectomized, adult golden hamsters was monitored under constant dim illumination. Thiourea treatment lengthened the period () of locomotor activity of thyroidectomized hamsters in comparison to pre-operative s and in comparison to the s of control hamsters. The results confirm hormonal modulation of the circadian system.Acknowledgments. This study was supported by grant HD-02982. L.J.B. was the recipient of a N.I.M.H. Traineeship (T32-MH-15860-01). We thank D. Frost, J. Budd, B. Ries, M. Darragh and J. Schutz for technical assistance. We are grateful to Drs I. Zucker and L. L. Rosenberg for guidance and helpful comments throughout this study. 相似文献
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Stochastic and genetic factors influence tissue-specific decline in ageing C. elegans 总被引:6,自引:0,他引:6
Herndon LA Schmeissner PJ Dudaronek JM Brown PA Listner KM Sakano Y Paupard MC Hall DH Driscoll M 《Nature》2002,419(6909):808-814
The nematode Caenorhabditis elegans is an important model for studying the genetics of ageing, with over 50 life-extension mutations known so far. However, little is known about the pathobiology of ageing in this species, limiting attempts to connect genotype with senescent phenotype. Using ultrastructural analysis and visualization of specific cell types with green fluorescent protein, we examined cell integrity in different tissues as the animal ages. We report remarkable preservation of the nervous system, even in advanced old age, in contrast to a gradual, progressive deterioration of muscle, resembling human sarcopenia. The age-1(hx546) mutation, which extends lifespan by 60-100%, delayed some, but not all, cellular biomarkers of ageing. Strikingly, we found strong evidence that stochastic as well as genetic factors are significant in C. elegans ageing, with extensive variability both among same-age animals and between cells of the same type within individuals. 相似文献
259.
Epiparasitic plants specialized on arbuscular mycorrhizal fungi 总被引:21,自引:0,他引:21
Bidartondo MI Redecker D Hijri I Wiemken A Bruns TD Domínguez L Sérsic A Leake JR Read DJ 《Nature》2002,419(6905):389-392
Over 400 non-photosynthetic species from 10 families of vascular plants obtain their carbon from fungi and are thus defined as myco-heterotrophs. Many of these plants are epiparasitic on green plants from which they obtain carbon by 'cheating' shared mycorrhizal fungi. Epiparasitic plants examined to date depend on ectomycorrhizal fungi for carbon transfer and exhibit exceptional specificity for these fungi, but for most myco-heterotrophs neither the identity of the fungi nor the sources of their carbon are known. Because many myco-heterotrophs grow in forests dominated by plants associated with arbuscular mycorrhizal fungi (AMF; phylum Glomeromycota), we proposed that epiparasitism would occur also between plants linked by AMF. On a global scale AMF form the most widespread mycorrhizae, thus the ability of plants to cheat this symbiosis would be highly significant. We analysed mycorrhizae from three populations of Arachnitis uniflora (Corsiaceae, Monocotyledonae), five Voyria species and one Voyriella species (Gentianaceae, Dicotyledonae), and neighbouring green plants. Here we show that non-photosynthetic plants associate with AMF and can display the characteristic specificity of epiparasites. This suggests that AMF mediate significant inter-plant carbon transfer in nature. 相似文献
260.
Transcriptional co-activator PGC-1 alpha drives the formation of slow-twitch muscle fibres 总被引:62,自引:0,他引:62
Lin J Wu H Tarr PT Zhang CY Wu Z Boss O Michael LF Puigserver P Isotani E Olson EN Lowell BB Bassel-Duby R Spiegelman BM 《Nature》2002,418(6899):797-801