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31.
32.
Clutton SM Townsend KM Goodhead DT Ansell JD Wright EG 《Cell death and differentiation》1996,3(1):141-148
Embryonal stem cells have been used to study the effects of environmentally relevant doses of radiation on cell death and differentation. The ES cells were found to have a greater than 60% chance of surviving the traversal of a single alpha-particle, the lowest possible dose of high linear energy transfer radiation a cell may receive. The ES cells appeared to possess the cell cycle checkpoints believed to prevent the transmission of the radiation damage. However, delayed effects were observed in the progeny. An increased incidence of apoptosis and haempoietic differentiation capacity was found to persist in the ES cell population over many cell divisions. Since both cell death and differentiation are known to play a key role in tissue kinetics, an ES cell model will provide a valuable and versatile cell system for studying the role of cell death and differentiation in the pathology of radiogenic diseases. 相似文献
33.
Richard J. Bold Jin Ishizuka Srinivasan Rajaraman †J. Regino Perez-Polo Courtney M. Townsend Jr. James C. Thompson 《Journal of neurochemistry》1995,64(6):2622-2628
Abstract: Carcinoid tumors are a group of neuroendocrine neoplasms distributed widely throughout the body but most commonly occurring in the gut. These tumors retain many characteristics of their neural crest origin, including secretion of neuroactive peptides and responsiveness to neurotrophic substances. Nerve growth factor (NGF), a neurotrophic protein involved in maintenance and differentiation of peripheral sympathetic and sensory neurons, regulates growth of several neural tumor cells by inducing a differentiated phenotype and subsequent inhibition of cell growth rate. We examined the actions of NGF in a functioning human pancreatic carcinoid cell line (termed BON). NGF has no effect on the cytoarchitecture or constitutive secretion of bioamines in this carcinoid cell line. NGF, however, stimulates the in vitro cellular proliferation of BON cells. BON cells possess mRNA for the NGF receptors (p75LNGFR and p140trkA ) and membrane-associated tyrosine kinase activity is increased in response to NGF. Both the mitogenic activity of NGF, as well as the receptor-linked tyrosine kinase activity, can be abrogated in BON cells by the trkA inhibitor K-252a and specific anti-NGF antibody. Our studies demonstrate that NGF is a mitogen for this carcinoid cell line without effect on cellular phenotype or cytoarchitecture. NGF may play a role in the development and progression of human carcinoid tumors. 相似文献
34.
Cloning of the mgtE Mg2+ transporter from Providencia stuartii and the distribution of mgtE in gram-negative and gram-positive bacteria. 总被引:1,自引:1,他引:0
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D E Townsend A J Esenwine J George rd D Bross M E Maguire R L Smith 《Journal of bacteriology》1995,177(18):5350-5354
The MM281 strain of Salmonella typhimurium possesses mutations in each of its three Mg2+ transport systems, requires 100 mM Mg2+ for growth, and was used to screen a genomic library from the gram-negative bacterium Providencia stuartii for clones that could restore the ability to grow without Mg2+ supplementation. The clones obtained also conferred sensitivity to Co2+, a phenotype similar to that seen with the S. typhimurium corA Mg2+ transport gene. The sequence of the cloned P. stuartii DNA revealed the presence of a single open reading frame, which was shown to express a protein with a gel molecular mass of 37 kDa in agreement with the deduced size of 34 kDa. Despite a phenotype similar to that of corA and the close phylogenetic relationship between P. stuartii and S. typhimurium, this new putative Mg2+ transporter lacks similarity to the CorA Mg2+ transporter and is instead homologous to MgtE, a newly discovered Mg2+ transport protein from the gram-positive bacterium Bacillus firmus OF4. The distribution of mgtE in bacteria was studied by Southern blot hybridization to PCR amplification products. In contrast to the ubiquity of the corA gene, which encodes the dominant constitutive Mg2+ influx system of bacteria, mgtE has a much more limited phylogenetic distribution. 相似文献
35.
Colin V. Beechey Simon T. Ball K. M. Stuart Townsend Janet Jones 《Mammalian genome》1997,8(4):236-240
Mouse Chromosome (Chr) 7 distal to band F3 on the physical map is known to be subject to imprinting, maternal duplication
(MatDp) of the region leading to a late embryonic lethality, while paternal duplication (PatDp) causes death in utero before
11.5 dpc. Using a new mouse reciprocal translocation T(7;11)65H to produce MatDp for distal Chr 7, we have mapped the region
subject to imprinting more precisely to bands 7F4/F5 on the cytogenetic map. Fluorescence in situ hybridization (FISH) studies
on mitotic and meiotic chromosomes of a T65H heterozygote show that the imprinted gene Igf2 is located in the same region. This was confirmed by the finding that embryos with MatDp of bands 7F4/F5 did not express
Igf2. We suggest that other members of the imprinted domain containing Igf2, namely Mash2, H19, Ins2, and p57
K1P2
, are also located in 7F4/F5 and that some or all of these genes may be responsible for the two imprinting lethalities seen
with MatDp and PatDp for this region.
Received: 13 October 1996 / Accepted: 8 December 1996 相似文献
36.
Characterization of humoral and CD4+ cellular responses after genetic immunization with retroviral vectors expressing different forms of the hepatitis B virus core and e antigens.
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M Sllberg K Townsend M Chen J O'Dea T Banks D J Jolly S M Chang W T Lee D R Milich 《Journal of virology》1997,71(7):5295-5303
The humoral and CD4+ cellular immune responses in mice following genetic immunization with three retroviral vectors encoding different forms of hepatitis B virus core antigen (HBcAg) and e antigen (HBeAg) were analyzed. The retroviral vectors induced expression of intracellular HBcAg (HBc[3A4]), secreted HBeAg (HBe[5A2]), or an intracellular HBcAg-neomycin phosphoryltransferase fusion protein (HBc-NEO[6A3]). Specific antibody levels and immunoglobulin G isotype restriction were highly dependent on both the host major histocompatibility complex and the transferred gene. Humoral and CD4+ cellular HBcAg and/or HBeAg (HBc/eAg)-specific immune responses following retroviral vector immunization were of a lower magnitude but followed the same characteristics compared with those after immunization with HBc/eAg in adjuvant. Two factors influenced the humoral responses. First, in vivo depletion of CD8+ cells in HBc-NEO[6A3]-immunized H-2k mice abrogated both HBcAg-specific antibodies and in vitro-detectable cytotoxic T lymphocytes. Second, priming of H-2b mice with an HBc/eAg-derived T-helper (Th) peptide in adjuvant prior to retroviral vector immunization greatly enhanced the HBc/eAg-specific humoral responses to all three vectors, suggesting that insufficient HBc/eAg-specific CD4+ Th-cell priming limits the humoral responses. In conclusion, direct injection of retroviral vectors seems to be effective in priming HBc/eAg-specific CD8+ but comparatively inefficient in priming CD4+ Th cells and subsequently specific antibodies. However, the limited HBc/eAg-specific CD4+ cell priming can effectively be circumvented by prior administration of a recombinant or synthetic form of HBc/eAg in adjuvant. 相似文献
37.
Pseudonitzschia pungens f.multiseries was cultured in 20-L polycarbonate carboys, 350-L fibreglass columns and 500-L plastic bags to determine the effects of medium enrichment and scale of culture on cell yield, production of cellular domoic acid and formation of fatty acids, particularly the potential tracer acid 16:4n-1. Cell concentrations were highest in seawater enriched with stock levels of nitrate and phosphate, but with double the stock level of silicate, at all scales of culture. Cellular toxin in 20, 350 and 500-L cultures averaged 0.32, 0.04 and 2.56 pg cell-1 and was independent of medium used. The order of magnitude difference in levels of cellular toxin was considered to reflect the varying levels of irradiance within the culture vessels. Support was given to this by the significant difference in content of total cellular fatty acids, due principally to the algal storage acid 16: 1n-7, which is known to be influenced by irradiance. Levels of cellular domoic acid correlated significantly with total fatty acids in 350 and 500-L cultures. Bag cultures producing significantly higher levels of cellular domoic acid provided lower relative proportions of 16:4n-1, which limited its use as a tracer for food-web studies. 相似文献
38.
39.
Steven G. Chrysant M.D.Ph.D. Susan M. Townsend B.S. Robert D. Lindeman M.D. Edward D. Frohlich M.D. 《Life sciences》1977,20(12):1953-1960
The possible effects of renal vasoconstriction from anesthesia and surgery on water excretion after hypotonic volume expansion (HVE) were studied in 18 well conditioned anesthetized dogs, with and without the infusion of phenoxybenzamine and acetylcholine into the renal artery of the cannulated kidney. In 6 dogs (Group 1 - Control) whose renal artery was infused with isosmotic saline, HVE resulted in a bilateral increase in GFR and UV (p < .05). ERPF, Cosm, CH2O, UNaV, UKV, RBF, RVR and MAP did not change significantly. In 6 other dogs (Group 2), whose cannulated kidney was infused with phenoxybenzamine 50 μg/min before and during HVE, GFR increased on the infused side while CH2O and UV increased bilaterally (p < .05). ERPF, Cosm, UNaV, UKV, RBF, RVR and MAP were not affected significantly. The addition of ADH, 2 mu/min into the phenoxybenzamine infusate, decreased ERPF, RBF and RVR bilaterally and CH2O on the infused side (p < .05). It had no effect upon GFR, Cosm, UNaV, UKV and MAP. In another 6 dogs, (Group 3), whose cannulated renal artery was infused with acetylcholine (20 μg/min) before and during HVE, CH2O, UV and RVR increased bilaterally (p < .05). ERPF and RBF decreased bilaterally (p < .05), whereas GFR, Cosm, UNaV and MAP were unaffected. UKV decreased on the infused side (p < .05). The addition of ADH (2 mu/min)_into the acetylcholine infusate, decreased CH2O bilaterally and increased Cosm and UKV on the control side (p < .05). It had no effect on ERPF, GFR, UV, UNaV, RBF, RVR and MAP. These observations suggest that anesthesia and surgery produce renal vasoconstriction and this together with increased ADH release, interfere with water excretion by the kidney. Previous renal vasodilation prevents these influences of anesthesia and surgery. 相似文献
40.
Summary Rare mutations that alter the substrate specificity of proline permease cluster in discrete regions of theputP gene, suggesting that they may replace amino acids at the active site of the enzyme. IfputP substrate specificity mutations directly alter the active site of proline permease, the mutants should show specific defects in the kinetics of proline transport. In order to test this prediction, we examined the kinetics of threeputP substrate specificity mutants. One class of mutation increases theK
m
over 120-fold but only decreases theV
max fourfold. SuchK
m
mutants may be specifically defective in substrate recognition, thus identifying an amino acid critical for substrate binding. Another class of mutation decreases theV
max 80-fold without changing theK
m
.V
max mutants appear to alter the rate of substrate translocation without affecting the substrate binding site. The last class of mutation alters both theK
m
andV
max of proline transport. These results indicate that substrate specificity mutations alter amino acids critical for Na+/proline symport. 相似文献