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排序方式: 共有247条查询结果,搜索用时 31 毫秒
91.
92.
Background
Comparative genomic data among organisms allow the reconstruction of their phylogenies and evolutionary time scales. Molecular timings have been recently used to suggest that environmental global change have shaped the evolutionary history of diverse terrestrial organisms. Living xenarthrans (armadillos, anteaters and sloths) constitute an ideal model for studying the influence of past environmental changes on species diversification. Indeed, extant xenarthran species are relicts from an evolutionary radiation enhanced by their isolation in South America during the Tertiary era, a period for which major climate variations and tectonic events are relatively well documented. 相似文献93.
JP Herv s J. Martí -Clú a A. Mu oz-Garcí a MC Santa-Cruz 《Biotechnic & histochemistry》2002,77(1):27-35
We have optimised an indirect immunoperoxidase technique demonstrating bromodeoxyuridine (BrdU) incorporation into dividing cells for cerebellar tissue sections of four-day-old rats injected with this marker. This permits confident identification of granule-cell precursors engaged in DNA synthesis in the external granular layer of the developing cerebellum. Preservation of BrdU immunoreactivity is attained using methanol/acetic acid fixation and different pretreatments before immunostaining, while unlabeled nuclei can be recognized clearly after Feulgen or hematoxylin counterstaining. We established conditions to ensure satisfactory BrdU uptake without affecting cell-cycle progression during the postlabeling time period. The dose of BrdU employed provides saturation S-phase labeling from at least 1 h after BrdU delivery. Various kinetic parameters and phase durations have been determined in experiments involving a single injection or cumulative labeling sequences, and the cycle time was calculated based on two models of generative behavior: steady-state and exponential growth. The working hypothesis of steadystate kinetics can be adopted successfully if the existence of neuroblasts with different proliferation rates is taken into account. 相似文献
94.
A J Van Oosterhout D Van Heuven-Nolsen S F De Boer J H Thijssen F P Nijkamp 《Life sciences》1989,44(1):57-65
Bacterial endotoxin induced a 38% decrease in the number of beta-adrenergic binding sites (Bmax) on splenic lymphocytes, four days after intraperitoneal administration to guinea pigs. No change in the affinity (Kd) for [125-I]-cyanopindolol ([125-I]-CYP) binding was observed. Incubation of guinea pig splenocytes in vitro with different concentrations of bacterial endotoxin for 24 hours resulted in an increased incorporation of [3H]-thymidine, a parameter for lymphocyte activation. Activation of splenic lymphocytes with the optimal endotoxin concentration of 100 micrograms/ml for 24 hours induced a 27% decrease in the Bmax whereas the Kd for [125-I]-CYP binding was not changed. Based on these findings, we speculate that activation of lymphocytes with endotoxin in vitro and in vivo is associated with a reduction in the number of beta-adrenergic binding sites on these cells. Anterior hypothalamic (AHA) lesions protected against the endotoxin-induced reduction in the number of beta-adrenergic binding sites on lymphocytes. The protective effect of these lesions could not be related to alterations in the plasma levels of cortisol, triiodothyronine (T3), thyroxine (T4), adrenaline and noradrenaline or to splenic noradrenaline content. Since AHA lesions have been shown to inhibit several lymphocyte functions, it is suggested that these lesions prevent lymphocyte activation after in vivo endotoxin administration and through this abrogate the reduction of the beta-adrenergic binding sites. 相似文献
95.
Castagnone-Sereno P; Semblat JP; Leroy F; Abad P 《Molecular biology and evolution》1998,15(9):1115-1122
A highly abundant satellite DNA comprising 20% of the Meloidogyne fallax
(Nematoda, Tylenchida) genome was cloned and sequenced. The satellite
monomer is 173 bp long and has a high A + T content of 72.3%, with frequent
runs of A's and T's. The sequence variability of the monomers is 2.7%,
mainly due to random distribution of single-point mutations. A search for
evidence of internal repeated subunits in the monomer sequence revealed a
6-bp motif (AAATTT) for which five degenerated repeats, differing by just a
single base pair, could be identified. Pairwise comparison of the M. fallax
satellite with those from the sympatric species Meloidogyne chitwoodi and
Meloidogyne hapla revealed a high sequence similarity (68.39%) with one
satellite DNA subfamily in M. chitwoodi, which indicated an unexpected
close relationship between them. Given the high copy number and the extreme
sequence homogeneity among monomeric units, it may be assumed that the
satellite DNA of M. fallax could have evolved through some recent and
extensive amplification burst in the nematode genome. In this case, its
relatively short life would not yet have allowed the accumulation of random
mutations in independent amplified repeats. Considering the morphological
resemblance between the two species and their ability to produce
interspecific fertile hybrids under controlled conditions, these results
indicate that M. fallax may share a common ancestor with M. chitwoodi, from
which it could have diverged recently. All these data suggest that M.
fallax could be the result of a recent speciation process and show that
Meloidogyne satellite DNAs may be of interest to resolve phylogenetic
relationships among closely related species from this genus.
相似文献
96.
The excretion of metabolites of cortisol and aldosterone in male patients on haemodialysis treatment
A single intravenous injection of 14C-cortisol and 3H-aldosterone was given to four male uraemic patients on haemodialysis (HD) treatment. The excretion of radioactivity was measured during two weeks in urine, HD fluid and faeces. In two patients, who were injected just before dialysis, large amounts of radioactivity were eliminated in the HD fluid (38 % and 56 % for 3H, 45 % and 57 % for 14C) and minor amounts were found in the urine (< 5 %); in the faeces respectively 32 % and 30 % of 3H and 18 % and 26 % of 14C were excreted. Two patients who were injected immediately after dialysis (and who also had a somewhat better kidney function) excreted larger amounts of radioactivity in the urine (10 % and 24 % for 3H, 13 % and 41 % for 14C) and in the faeces (44 % and 62 % for 3H, 29 % and 37 % for14C), while in the HD fluid respectively 18 % and 4 % of 3H and 30 % and 12 % of 14C was eliminated. The plasma radioactivity just before and just after dialysis showed a very good correlation (r = 0.96 to 0.99, p < 0.001) with the radioactivity eliminated in the first and last hour of HD treatment. Between HD treatments, the radioactivity in plasma did not change or decreased only very little. This finding suggests that metabolites of Cortisol and aldosterone to be excreted in the faeces, are very quickly removed from the circulation. 相似文献
97.
98.
Tim?Lu Christine?M?Costello Peter?JP?Croucher Robert?H?sler Günther?Deuschl Stefan?SchreiberEmail author 《BMC bioinformatics》2005,6(1):37
Background
Normalization is the process of removing non-biological sources of variation between array experiments. Recent investigations of data in gene expression databases for varying organisms and tissues have shown that the majority of expressed genes exhibit a power-law distribution with an exponent close to -1 (i.e. obey Zipf's law). Based on the observation that our single channel and two channel microarray data sets also followed a power-law distribution, we were motivated to develop a normalization method based on this law, and examine how it compares with existing published techniques. A computationally simple and intuitively appealing technique based on this observation is presented. 相似文献99.
Summary In order to improve the ultrastructural preservation of the female gametophyte ofPetunia x hybrida andBrassica napus we tested several cryofixation techniques and compared the results with those of conventional chemical fixation methods. Ovules fixed with glutaraldehyde and osmium tetroxide in the presence or absence of potassium ferrocyanide showed poor cell morphological and ultrastructural preservation. In ovules cryo-fixed by plunging into liquid propane, the cell morphology was well preserved. However, at the ultrastructural level structure-distorting ice crystals were detected in all tissues. Due to the large size of the ovules, cryofixation by plunging in liquid propane is not adequate for ultrastructural studies. In contrast,P. x hybrida andB. napus ovules cryo-fixed by high pressure freezing showed improved cell morphological as well as ultrastructural preservation of the embryo sac and the surrounding integumentary tissues. The contrast of the cellular membranes after freeze substitution with 2% osmium tetroxide and 0.1% uranyl acetate in dry acetone was high. At the ultrastructural level, the most prominent improvements were: straight plasma membranes which were appressed to the cell walls; turgid appearing organelles with smooth surface contours; minimal extraction of cytoplasmic and extracellular substances. In contrast to the chemically fixed ovules, in high pressure frozen ovules numerous microtubules and multivesicular bodies could be distinguished. 相似文献
100.