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排序方式: 共有139条查询结果,搜索用时 15 毫秒
1.
Ultrastructural features of egg development in oviparae of the vetch aphid, Megoura viciae buckton 总被引:1,自引:0,他引:1
In the ovaries of the oviparous morph of the aphid, Megoura viciae, resting oocytes are located in the basal region of each germarium. During previtellogenic egg development, electron-dense spheres appear in the ooplasm. During vitellogenesis a brush border develops at the oolemma, and numerous protein and lipid-like spheres accumulate in the egg cytoplasm. Follicle cells are of two morphologically distinct types, termed 'type 1' and 'type 2' follicle cells. Unlike the more numerous 'type 1' cell, 'type 2' cells do not become patent. The acellular tunica propria exterior to follicle cell apices remains intact throughout egg development. During late vitellogenesis symbiont invasion of eggs takes place via 'receptor' cells encircling the pedicel at the posterior egg pole. These cells shrink and/or degenerate to create intercellular spaces that facilitate symbiont transmission. The end of vitellogenesis is marked by vitelline membrane formation and secretion of the chorionic layers, at which time the next egg in the ovariole undergoes final stages of previtellogenic growth and enters vitellogenesis. 相似文献
2.
K Abrahamsen H L Kong A Mastrangeli D Brough A Lizonova R G Crystal E Falck-Pedersen 《Journal of virology》1997,71(11):8946-8951
A strategy for constructing replication-defective adenovirus vectors from non-subgroup C viruses has been successfully demonstrated with adenovirus type 7 strain a (Ad7a) as the prototype. An E1A-deleted Ad7a reporter virus expressing the chloramphenicol acetyltransferase (CAT) gene from the cytomegalovirus promoter enhancer was constructed with DNA fragments isolated from Ad7a, an Ad7a recombination reporter plasmid, and the 293 cell line. The Ad7a-CAT virus particle transduces A549 cells as efficiently as Ad5-based vectors. Intravenous infections in a murine model indicate that the Ad7a-CAT virus infects a variety of tissues, with maximal levels of CAT gene expression found in the liver. The duration of Ad7a-CAT transgene expression in the liver was maximally maintained 2 weeks postinfection, with a decline to baseline activity by the week 4 postinfection. Ad7a-CAT represents the first example of a non-subgroup C E1A- adenovirus gene transfer vector. 相似文献
3.
Justin S. LaFountaine Leena Kumari Prasad Chris Brough Dave A. Miller James W. McGinity Robert O. WilliamsIII 《AAPS PharmSciTech》2016,17(1):120-132
Thermal processing technologies continue to gain interest in pharmaceutical manufacturing. However, the types and grades of polymers that can be utilized in common thermal processing technologies, such as hot-melt extrusion (HME), are often limited by thermal or rheological factors. The objectives of the present study were to compare and contrast two thermal processing methods, HME and KinetiSol® Dispersing (KSD), and investigate the influence of polymer type, polymer molecular weight, and drug loading on the ability to produce amorphous solid dispersions (ASDs) containing the model compound griseofulvin (GRIS). Dispersions were analyzed by a variety of imaging, solid-state, thermal, and solution-state techniques. Dispersions were prepared by both HME and KSD using polyvinylpyrrolidone (PVP) K17 or hydroxypropyl methylcellulose (HPMC) E5. Dispersions were only prepared by KSD using higher molecular weight grades of HPMC and PVP, as these could not be extruded under the conditions selected. Powder X-ray diffraction (PXRD) analysis showed that dispersions prepared by HME were amorphous at 10% and 20% drug load; however, it showed significant crystallinity at 40% drug load. PXRD analysis of KSD samples showed all formulations and drug loads to be amorphous with the exception of trace crystallinity seen in PVP K17 and PVP K30 samples at 40% drug load. These results were further supported by other analytical techniques. KSD produced amorphous dispersions at higher drug loads than could be prepared by HME, as well as with higher molecular weight polymers that were not processable by HME, due to its higher rate of shear and torque output. 相似文献
4.
Wu S Sangerman J Li M Brough GH Goodman SR Stevens T 《The Journal of cell biology》2001,154(6):1225-1233
Mechanism(s) underlying activation of store-operated Ca2+ entry currents, ISOC, remain incompletely understood. F-actin configuration is an important determinant of channel function, although the nature of interaction between the cytoskeleton and ISOC channels is unknown. We examined whether the spectrin membrane skeleton couples Ca2+ store depletion to Ca2+ entry. Thapsigargin activated an endothelial cell ISOC (-45 pA at -80 mV) that reversed at +40 mV, was inwardly rectifying when Ca2+ was the charge carrier, and was inhibited by La3+ (50 microM). Disruption of the spectrin-protein 4.1 interaction at residues A207-V445 of betaSpIISigma1 decreased the thapsigargin-induced global cytosolic Ca2+ response by 50% and selectively abolished the endothelial cell ISOC, without altering activation of a nonselective current through cyclic nucleotide-gated channels. In contrast, disruption of the spectrin-actin interaction at residues A47-K186 of betaSpIISigma1 did not decrease the thapsigargin-induced global cytosolic Ca2+ response or inhibit ISOC. Results indicate that the spectrin-protein 4.1 interaction selectively controls ISOC, indicating that physical coupling between calcium release and calcium entry is reliant upon the spectrin membrane skeleton. 相似文献
5.
Xie H Patching SG Gallagher MP Litherland GJ Brough AR Venter H Yao SY Ng AM Young JD Herbert RB Henderson PJ Baldwin SA 《Molecular membrane biology》2004,21(5):323-336
NupG from Escherichia coli is the archetype of a family of nucleoside transporters found in several eubacterial groups and has distant homologues in eukaryotes, including man. To facilitate investigation of its molecular mechanism, we developed methods for expressing an oligohistidine-tagged form of NupG both at high levels (>20% of the inner membrane protein) in E. coli and in Xenopus laevis oocytes. In E. coli recombinant NupG transported purine (adenosine) and pyrimidine (uridine) nucleosides with apparent K(m) values of approximately 20-30 microM and transport was energized primarily by the membrane potential component of the proton motive force. Competition experiments in E. coli and measurements of uptake in oocytes confirmed that NupG was a broad-specificity transporter of purine and pyrimidine nucleosides. Importantly, using high-level expression in E. coli and magic-angle spinning cross-polarization solid-state nuclear magnetic resonance, we have for the first time been able directly to measure the binding of the permeant ([1'-(13)C]uridine) to the protein and to assess its relative mobility within the binding site, under non-energized conditions. Purification of over-expressed NupG to near homogeneity by metal chelate affinity chromatography, with retention of transport function in reconstitution assays, was also achieved. Fourier transform infrared and circular dichroism spectroscopy provided further evidence that the purified protein retained its 3D conformation and was predominantly alpha-helical in nature, consistent with a proposed structure containing 12 transmembrane helices. These findings open the way to elucidating the molecular mechanism of transport in this key family of membrane transporters. 相似文献
6.
One of the most complex issues in the cloud computing environment is the problem of resource allocation so that, on one hand, the cloud provider expects the most profitability and, on the other hand, users also expect to have the best resources at their disposal considering the budget constraints and time. In most previous work conducted, heuristic and evolutionary approaches have been used to solve this problem. Nevertheless, since the nature of this environment is based on economic methods, using such methods can decrease response time and reducing the complexity of the problem. In this paper, an auction-based method is proposed which determines the auction winner by applying game theory mechanism and holding a repetitive game with incomplete information in a non-cooperative environment. In this method, users calculate suitable price bid with their objective function during several round and repetitions and send it to the auctioneer; and the auctioneer chooses the winning player based the suggested utility function. In the proposed method, the end point of the game is the Nash equilibrium point where players are no longer inclined to alter their bid for that resource and the final bid also satisfies the auctioneer’s utility function. To prove the response space convexity, the Lagrange method is used and the proposed model is simulated in the cloudsim and the results are compared with previous work. At the end, it is concluded that this method converges to a response in a shorter time, provides the lowest service level agreement violations and the most utility to the provider. 相似文献
7.
Rescue and production of vaccine and therapeutic adenovirus vectors expressing inhibitory transgenes
Gall JG Lizonova A EttyReddy D McVey D Zuber M Kovesdi I Aughtman B King CR Brough DE 《Molecular biotechnology》2007,35(3):263-273
Expression of certain transgenes from an adenovirus vector can be deleterious to its own replication. This can result in the
inhibition of virus rescue, reduced viral yields, or, in the worst case, make it impossible to construct a vector expressing
the inhibiting transgene product. A gene regulation system based on the tet operon was used to allow the rescue and efficient growth of adenovectors that express transgenes to high levels. A key advantage
to this system is that repression of transgene expression is mediated by the packaging cell line, thus, expression of regulatory
products from the adenovector are not required. This provides a simple, broadly applicable system wherein transgene repression
is constitutive during vector rescue and growth and there is no effect on adenovector-mediated expression of gene products
in transduced cells. Several high-level expression vectors based on first- and second-generation adenovectors were rescued
and produced to high titer that otherwise could not be grown. Yields of adenovectors expressing inhibitory transgene products
were increased, and the overgrowth of cultures by adenovectors with nonfunctional expression cassettes was prevented. The
gene regulation system is a significant advancement for the development of adenovirus vectors for vaccine and other gene transfer
applications. 相似文献
8.
Annemarie MM Vlaar Angela EP Bouwmans Marinus JPG van Kroonenburgh Werner H Mess Selma C Tromp Piet GWM Wuisman Alfons GH Kessels Ania Winogrodzka Wim EJ Weber 《BMC neurology》2007,7(1):28
Background
Parkinson's disease (PD) is the second most common neurodegenerative disorder. As there is no definitive diagnostic test, its diagnosis is based on clinical criteria. Recently transcranial duplex scanning (TCD) of the substantia nigra in the brainstem has been proposed as an instrument to diagnose PD. We and others have found that TCD scanning of substantia nigra duplex is a relatively accurate diagnostic instrument in patients with parkinsonian symptoms. However, all studies on TCD so far have involved well-defined, later-stage PD patients, which will obviously lead to an overestimate of the diagnostic accuracy of TCD. 相似文献9.
Background
The ability to regulate transgene expression has many applications, mostly concerning the analysis of gene function. Desirable induction characteristics, such as low un-induced expression, high induced expression and limited cellular heterogeneity, can be seriously impaired by chromosomal position effects at the site of transgene integration. Many clones may therefore need to be screened before one with optimal induction characteristics is identified. Furthermore, such screens must be repeated for each new transgene investigated, and comparisons between clones with different transgenes is complicated by their different integration sites. 相似文献10.
Annerieke C van Groenestijn Ingrid GL van de Port Carin D Schröder Marcel WM Post Hepke F Grupstra Esther T Kruitwagen Harmen van der Linde Reinout O van Vliet Margreet GH van de Weerd Leonard H van den Berg Eline Lindeman 《BMC neurology》2011,11(1):1-11