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排序方式: 共有248条查询结果,搜索用时 15 毫秒
51.
52.
I J Gonzalez-Robayna T N Alliston P Buse G L Firestone J S Richards 《Molecular endocrinology (Baltimore, Md.)》1999,13(8):1318-1337
The responsiveness of granulosa cells to FSH (cAMP) changes as these cells switch from the proliferative stage in growing follicles to the terminally differentiated, nonproliferating stage after LH-induced luteinization. To analyze this transition, two well characterized culture systems were used. 1) Granulosa cells isolated from immature rats were cultured in serum-free medium, a system that permits analysis of dynamic, short-term responses to hormones/cAMP. 2) Granulosa cells from preovulatory (PO) follicles that have been exposed in vivo to surge concentrations of hCG (PO/ hCG) were cultured in medium containing 1% FBS, a system that permits analyses of cells that have undergo irreversible, long-term changes associated with luteinization. To analyze the biochemical basis for the switch in cAMP responsiveness, the localization of A-kinase pathway components was related to the expression of two cAMP target genes, aromatase (CYP19) and serum-and glucocorticoid-induced kinase (Sgk). Components of the A-kinase pathway were analyzed by Western blotting and indirect immunofluorescence using specific antibodies to the C subunit, RIIalpha/beta subunits, CREB (cAMP-regulatory element binding protein), phospho-CREB, CBP (CREB binding protein), and Sgk. Cellular levels of C subunit and CREB were similar in all cell types and hormone treatments. CREB and CBP were nuclear; RIIalpha/beta was restricted to a cytoplasmic basket-like structure. Addition of FSH to immature granulosa cells caused rapid nuclear import of C subunit within 1 h. Nuclear C subunit decreased by 6 h after FSH but could be rapidly reimported to the nucleus by the addition of forskolin at 6, 24, or 48 h. Nuclear C subunit was associated with the rapid but transient increases in phospho-CREB. FSH induced Sgk in a biphasic manner in which the protein was nuclear at 1 h and cytoplasmic at 48 h. Aromatase mRNA was only expressed at 24-48 h after FSH, a pattern that was not altered by phosphodiesterases or phosphatases. In the luteinized (PO/hCG) granulosa cells, immunoreactive C subunit was localized in a punctate pattern in the nucleus as well as to a cytoplasmic basket-like structure, a distribution pattern not altered by forskolin. Aromatase, Sgk, and phospho-CREB were expressed at elevated levels in a non-forskolin-responsive manner. Most notable, both phospho-CREB and Sgk were preferentially localized in a punctate pattern within the cytoplasm and not altered by forskolin. Collectively, these data indicate that when granulosa cells differentiate to luteal cells the subcellular localization (nuclear vs. cytoplasmic) of A-kinase pathway components changes markedly. Thus, either the mechanisms of nuclear import and export or the presence of distinct docking sites (and functions ?) dictate where A-kinase, phospho-CREB and Sgk are localized in granulosa cells compared with the terminally differentiated luteal cells. 相似文献
53.
Maria J. Cardoso Mark D. B. Eldridge Meri Oakwood Brooke Rankmore William B. Sherwin Karen B. Firestone 《Conservation Genetics》2009,10(6):1719-1733
Translocation is a strategy commonly used to maximize the persistence of threatened species, but it may sometimes lead to undesirable genetic consequences. The northern quoll (Dasyurus hallucatus) is a carnivorous marsupial that is critically endangered in Australia’s Northern Territory due to rapid population declines in areas recently colonized by the exotic cane toad Chaunus [Bufo] marinus. In 2003, 64 quolls were translocated to two offshore islands to establish insurance populations and reduce the species’ risk of extinction. In this study, we assessed genetic diversity at five microsatellite loci in the translocated populations, two endemic islands and three mainland populations. In the short-term (three generations), the translocated populations showed a slight but non-significant reduction in genetic diversity (A = 4.1–4.2; H e = 0.56–0.59) compared to the mainland source populations (A = 5.0–8.4; H e = 0.56–0.71). In comparison, high genetic erosion was observed in the endemic island populations (A = 1.5–2.9; H e = 0.11–0.34). Genetic bottlenecks were detected on both endemic islands and in one mainland population, indicating recent reductions in population size. Our results are consistent with previous studies describing greater losses of genetic diversity on islands compared to mainland populations. Divergence from ancestral allele frequencies in the translocated populations also suggests effects due to founder events. This study, although short-term, highlights the importance of continued monitoring for detecting changes in genetic diversity over time and makes a significant contribution to our understanding of the effects of founder events on island populations. 相似文献
54.
Kristen M. DeAngelis Whendee L. Silver Andrew W. Thompson Mary K. Firestone 《Environmental microbiology》2010,12(12):3137-3149
Rapidly fluctuating environmental conditions can significantly stress organisms, particularly when fluctuations cross thresholds of normal physiological tolerance. Redox potential fluctuations are common in humid tropical soils, and microbial community acclimation or avoidance strategies for survival will in turn shape microbial community diversity and biogeochemistry. To assess the extent to which indigenous bacterial and archaeal communities are adapted to changing in redox potential, soils were incubated under static anoxic, static oxic or fluctuating redox potential conditions, and the standing (DNA‐based) and active (RNA‐based) communities and biogeochemistry were determined. Fluctuating redox potential conditions permitted simultaneous CO2 respiration, methanogenesis, N2O production and iron reduction. Exposure to static anaerobic conditions significantly changed community composition, while 4‐day redox potential fluctuations did not. Using RNA : DNA ratios as a measure of activity, 285 taxa were more active under fluctuating than static conditions, compared with three taxa that were more active under static compared with fluctuating conditions. These data suggest an indigenous microbial community adapted to fluctuating redox potential. 相似文献
55.
Guma MK Abdeldaim Kristoffer Strålin Jens Korsgaard Jonas Blomberg Christina Welinder-Olsson Björn Herrmann 《BMC microbiology》2010,10(1):310
Background
Streptococcus pneumoniae and Haemophilus influenzae cause pneumonia and as Neisseria meningitidis they are important agents of meningitis. Although several PCR methods have been described for these bacteria the specificity is an underestimated problem. Here we present a quantitative multiplex real-time PCR (qmPCR) for detection of S. pneumoniae (9802 gene fragment), H. influenzae (omp P6 gene) and N. meningitidis (ctrA gene). The method was evaluated on bronchoalveolar lavage (BAL) samples from 156 adults with lower respiratory tract infection (LRTI) and 31 controls, and on 87 cerebrospinal fluid (CSF) samples from meningitis patients. 相似文献56.
King HD Yurgaitis D Willner D Firestone RA Yang MB Lasch SJ Hellström KE Trail PA 《Bioconjugate chemistry》1999,10(2):279-288
Immunoconjugates of monoclonal antibody BR96 and Doxorubicin have been prepared using a novel series of branched hydrazone linkers. Since each linker bound to the mAb carries two DOX molecules, the DOX/mAb molar ratios of these conjugates were approximately 16, twice that of those previously prepared with single-chain hydrazone linkers. The conjugates were stable at a physiological pH of 7, but released DOX rapidly at lysosomal pH 5. The branched series of BR96 conjugates demonstrated antigen-specific cytotoxicity, and were more potent in vitro than the single-chain conjugate on both a DOX (4-14-fold) and mAb (7-23-fold) basis. The results suggest that, by using the branched linker methodology, it is possible to significantly reduce the amount of mAb required to achieve antigen-specific cytotoxic activity. In this paper, the synthesis and in vitro biology of branched chain immunoconjugates are described. 相似文献
57.
Buse P Tran SH Luther E Phu PT Aponte GW Firestone GL 《The Journal of biological chemistry》1999,274(11):7253-7263
58.
Guan Y Rubenstein NM Failor KL Woo PL Firestone GL 《Molecular endocrinology (Baltimore, Md.)》2004,18(1):214-227
59.
60.
Using simulated data, we compared five methods of phylogenetic tree
estimation: parsimony, compatibility, maximum likelihood, Fitch-
Margoliash, and neighbor joining. For each combination of substitution
rates and sequence length, 100 data sets were generated for each of 50
trees, for a total of 5,000 replications per condition. Accuracy was
measured by two measures of the distance between the true tree and the
estimate of the tree, one measure sensitive to accuracy of branch lengths
and the other not. The distance-matrix methods (Fitch- Margoliash and
neighbor joining) performed best when they were constrained from estimating
negative branch lengths; all comparisons with other methods used this
constraint. Parsimony and compatibility had similar results, with
compatibility generally inferior; Fitch- Margoliash and neighbor joining
had similar results, with neighbor joining generally slightly inferior.
Maximum likelihood was the most successful method overall, although for
short sequences Fitch- Margoliash and neighbor joining were sometimes
better. Bias of the estimates was inferred by measuring whether the
independent estimates of a tree for different data sets were closer to the
true tree than to each other. Parsimony and compatibility had particular
difficulty with inaccuracy and bias when substitution rates varied among
different branches. When rates of evolution varied among different sites,
all methods showed signs of inaccuracy and bias.
相似文献