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991.
Higgins KJ Liu S Abdelrahim M Vanderlaag K Liu X Porter W Metz R Safe S 《Molecular endocrinology (Baltimore, Md.)》2008,22(2):388-402
17beta-Estradiol (E2) induces and represses gene expression in breast cancer cells; however, the mechanisms of gene repression are not well understood. In this study, we show that E2 decreases vascular endothelial growth factor receptor 2 (VEGFR2) mRNA levels in MCF-7 cells, and this gene was used as a model for investigating pathways associated with E2-dependent gene repression. Deletion analysis of the VEGFR2 promoter indicates that the proximal GC-rich motifs at -58 and -44 are critical for the E2-dependent decreased response in MCF-7 cells. Mutation or deletion of these GC-rich elements results in loss of hormone responsiveness and shows that the -60 to -37 region of the VEGFR2 promoter is critical for both basal and hormone-dependent decreased VEGFR2 expression in MCF-7 cells. Western blot, immunofluorescent staining, RNA interference, and EMSAs support a role for Sp proteins in hormone-dependent down-regulation of VEGFR2 in MCF-7 cells, primarily through estrogen receptor (ER)alpha/Sp1 and ERalpha/Sp3 interactions with the VEGFR2 promoter. Using chromatin immuno-precipitation and transient transfection/RNA interference assays we show that the ERalpha/Sp protein-promoter interactions are accompanied by recruitment of the co-repressors SMRT (silencing mediator of retinoid and thyroid hormone receptor) and NCoR (nuclear receptor corepressor) to the promoter and that SMRT and NCoR knockdown reverse E2-mediated down-regulation of VEGFR2 expression in MCF-7 cells. This study illustrates that both SMRT and NCoR are involved in E2-dependent repression of VEGFR2 in MCF-7 cells. 相似文献
992.
Genetic characterization of the Drosophila jaguar322 mutant reveals that complete myosin VI loss of function is not lethal 下载免费PDF全文
Myosin VI is an actin-based motor that has been implicated in many cellular processes. Studies in vertebrates have demonstrated that animals lacking this ubiquitously expressed myosin are viable. However in Drosophila, myosin VI loss of function has been thought to be lethal. We show here that complete loss of myosin VI is not lethal in flies and that the previously reported lethality of the null mutation (jar322) is most likely due to deletion of a neighboring gene. Maternally provided myosin VI does not account for the survival of myosin VI null animals. Mutant animals are recovered at a lower than expected Mendelian frequency, suggesting that myosin VI participates in processes which contribute to normal development, but its participation is not essential. 相似文献
993.
Androgens act on the CNS to affect motor function through interaction with a widespread distribution of intracellular androgen receptors (AR). This review highlights our work on androgens and process outgrowth in motoneurons, both in vitro and in vivo. The actions of androgens on motoneurons involve the generation of novel neuronal interactions that are mediated by the induction of androgen-dependent neurite or axonal outgrowth. Here, we summarize the experimental evidence for the androgenic regulation of the extension and regeneration of motoneuron neurites in vitro using cultured immortalized motoneurons, and axons in vivo using the hamster facial nerve crush paradigm. We place particular emphasis on the relevance of these effects to SBMA and peripheral nerve injuries. 相似文献
994.
Elizabeth A. Farley Kathryn E. Sieving Thomas A. Contreras 《Journal of Ornithology》2008,149(3):451-468
We developed sampling methods to characterize the participation of bird species in foraging flocks led by the Eastern Tufted
Titmouse (Baeolophus bicolor) in North-central Florida during winter, because standard field methods, developed primarily for permanent resident Neotropical
flocks, were intractable in our system. During January–February 2004 and November 2004–March 2005, we observed 55 mixed-species
flocks, recorded 40 potential flocking species [mean of 12.4 species (SD = 3.8; range 3–20), 26.3 individuals (SD = 12.2;
range 8–60), and 3.1 titmice (SD = 1.4; range 1–7), per flock]. Twenty-six species were observed frequently enough (>10% of
observations) to be included in analyses. We paired 60-min flock observations with 10-min point counts conducted in locations
used by flocks, but after flocks had moved more than 100 m away. This method yielded a measure of flocking propensity: the
ratio of the number of individuals observed in the flock versus during the point count for each species. We used regression
tree (RT) analysis to classify species into groupings according to their levels of flock participation, and to investigate
relationships between flocking propensity and various environmental and social factors that we measured. Our analysis identified
three clear species groups; “Nuclear/Regular Associate” (12 spp.; high/moderate), “Occasional Associate” (four spp.; moderate/low),
and “Non-joiner/Accidental” (ten spp.; low/no flocking propensity). Groupings were similar to schemes produced via more time-intensive
field methods. In order to contextualize grouping categories, we conducted a review of flocking group definitions and relevant
autecological information (e.g., interspecific sociality) about our study species. We found this method to be useful for geographically
extensive sampling of species’ participation in mixed-species flocks, despite high inter-flock variability in species composition
and limited labor. 相似文献
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997.
Many species of rhizobial bacteria can invade their plant hosts and induce development of symbiotic nitrogen-fixing nodules only if they are able to produce an acidic exopolysaccharide (EPS) with certain structural and molecular weight characteristics.1–3 Sinorhizobium meliloti that produces the functional form of the exopolysaccharide succinoglycan induces formation of invasion structures called infection threads in the root hair cells of its plant hosts alfalfa and Medicago truncatula. However, S. meliloti mutants that cannot produce succinoglycan are not able to induce infection thread formation, resulting in an early arrest of nodule development and in nitrogen starvation of the plant. Mounting evidence has suggested that succinoglycan acts as a signal to these host plants to permit the entry of S. meliloti. Now, our microarray screen and functional category analysis of differentially-expressed genes show that M. truncatula plants inoculated with wild type S. meliloti receive a signal to increase their translation capacity, alter their metabolic activity and prepare for invasion, while those inoculated with a succinoglycan-deficient mutant do not receive this signal, and also more strongly express plant defense genes.Key words: nitrogen fixation, nodule, succinoglycan, microarray, legume, rhizobial bacteria, Sinorhizobium meliloti, Medicago truncatula, infection thread, root hair 相似文献
998.
Kathryn E. Stoner Karla A. O.-Salazar Roxana C. R.-Fernández Mauricio Quesada 《Biodiversity and Conservation》2003,12(2):357-373
We estimate fluctuations in population size and sex ratio, documentbreeding behavior and reproduction, and determine the diet of a population ofthe lesser long-nosed bat, Leptonycteris curasoae, in anisland cave in Chamela Bay, Jalisco, Mexico, with monthly sampling during anannual cycle (October 1999–October 2000). Based on the area of thecave's ceiling and wall covered with L. curasoae inrelation to the potential roost area without them, in 1999 the abundanceincreased from 80% in October to 100% in November and December. In 2000 thepopulation decreased to 80% in January, 50% in February, 30% in March, 20% inApril, 10% in May, 5% in June and July, and less than 1% in August. Thepopulation rapidly increased to 60% in September and to 80% in October.Throughout the year there were significantly more males than females; however,there was significant heterogeneity over months. In September–Novemberthere were more females, but in December–August there were more malespresent. The majority of pregnant and lactating females were observed fromDecember to March and in July, while males were reproductive fromSeptember–January and in May–June. Breeding activity was observed inthe cave in November–December. Twenty-six species of plants were consumedduring the year, based on pollen identification from fecal samples. Bombacaceousspecies were the most important component of the diet from January to May andCactaceae were most important in June–September. Peak abundance and reproductive activitycoincided with peak flower resource availability, which occurred between Octoberand January and in June–July. The year-round presence and reproductiveactivity of L. curasoae at this site throughout the yeardemonstrate that many individuals are annual residents in this area and indicatethe importance of this roosting site. In order to develop a successfulconservation program for L. curasoae, in addition toprotecting migratory corridors and northern maternity roosts, it is equallyimportant to identify and protect areas that function as breeding colonies andyear-round sanctuaries for resident populations in the south. 相似文献
999.
Kathryn M. Johnson Lara Swenson Anthony W. Opipari Jr. Rolf Reuter Nawid Zarrabi Carol A. Fierke Michael Börsch Gary D. Glick 《Biopolymers》2009,91(10):830-840
The mitochondrial F1Fo‐ATPase performs the terminal step of oxidative phosphorylation. Small molecules that modulate this enzyme have been invaluable in helping decipher F1Fo‐ATPase structure, function, and mechanism. Aurovertin is an antibiotic that binds to the β subunits in the F1 domain and inhibits F1Fo‐ATPase‐catalyzed ATP synthesis in preference to ATP hydrolysis. Despite extensive study and the existence of crystallographic data, the molecular basis of the differential inhibition and kinetic mechanism of inhibition of ATP synthesis by aurovertin has not been resolved. To address these questions, we conducted a series of experiments in both bovine heart mitochondria and E. coli membrane F1Fo‐ATPase. Aurovertin is a mixed, noncompetitive inhibitor of both ATP hydrolysis and synthesis with lower Ki values for synthesis. At low substrate concentrations, inhibition is cooperative suggesting a stoichiometry of two aurovertin per F1Fo‐ATPase. Furthermore, aurovertin does not completely inhibit the ATP hydrolytic activity at saturating concentrations. Single‐molecule experiments provide evidence that the residual rate of ATP hydrolysis seen in the presence of saturating concentrations of aurovertin results from a decrease in the binding change mechanism by hindering catalytic site interactions. The results from these studies should further the understanding of how the F1Fo‐ATPase catalyzes ATP synthesis and hydrolysis. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 830–840, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com 相似文献
1000.