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排序方式: 共有395条查询结果,搜索用时 15 毫秒
1.
Glen R. Needham Rosemarie Rosell Lewis Greenwald 《Experimental & applied acarology》1990,10(2):83-104
We describe the ultrastructure of type-I salivary-gland acini in two argasid and two ixodid species. The basic cell types in the agranular or type-I acini, and their associations, are very similar in argasids and ixodids; therefore, we propose an anatomical nomenclature for cells in the type-I acinus based on the adult ixodidsAmblyomma americanum andDermacentor variabilis, and the argasid adultArgas (Persicargas) arboreus and on nymphalOrnithodoros moubata. Four cell types were present in all specimens: one central lamellate cell, a variable number of peripheral lamellate cells, a variable number of peritubular cells depending on the species, and one circumlumenal cell. The lamellate cells had infolded basal plasma membranes that presented an amplified surface area to the hemolymph. These cells most likely secreted the fluid involved in water vapor uptake by ticks. ForAmblyomma americanum females, abundant K+-dependent, ouabain-sensitive Na+, K+-ATPase complexes were located on the infolded basal plasma membranes of the lamellate cells. Apical membranes of the lamellate cells, and plasma membranes of other cell types in the acinus had little or no evidence of Na+, K+-ATPase activity. Only the central lamellate cell extended from the hemolymph of the acinus to its lumen; peripheral cells did not contact the lumen. Except when the ticks were rehydrating, lipid inclusions were common features in the lamellate cells of the ixodids. Lipid inclusions were not seen in argasid type I acini; however, glycogen deposits were common. To determine if acinar cells respond to the changing hydration state of the tick, unfed femaleA. americanum were subjected to dehydration/rehydrating conditions. During rehydration, mitochondria in the lamellate cells changed from a matrix of medium electron-density and intermembrane space (orthodox configuration) to a matrix of greater density and larger intermembrane space (condensed configuration). The orthodox configuration was consistently observed in control and dehydrating ticks. The condensed configuration was the norm for mitochondria in lamellate cells of rehydrating ticks. Lipid inclusions were depleted in the rehydrating ticks compared to control or dehydrating ticks. Acini appeared to be reverting to the control or desiccated state when ticks were returned to low humidity, suggesting that these changes were cyclical. Nymphs ofO. moubata subjected to the same dehydration/rehydrating conditions showed no obvious ultrastructural changes. 相似文献
2.
LCR/MEL: a versatile system for high-level expression of heterologous proteins in erythroid cells. 总被引:11,自引:0,他引:11 下载免费PDF全文
M Needham C Gooding K Hudson M Antoniou F Grosveld M Hollis 《Nucleic acids research》1992,20(5):997-1003
We have used the human globin locus control region (LCR) to assemble an expression system capable of high-level, integration position-independent expression of heterologous genes and cDNAs in murine erythroleukaemia (MEL) cells. The cDNAs are inserted between the human beta-globin promoter and the second intron of the human beta-globin gene, and this expression cassette is then placed downstream of the LCR and transfected into MEL cells. The cDNAs are expressed at levels similar to those of the murine beta-globin in the induced MEL cells. Heterologous genomic sequences can also be expressed at similar levels when linked to to the LCR and beta-globin promoter. In addition we demonstrate that, after induction of differentiation, MEL cells are capable of secreting heterologous proteins over a prolonged time period, making this system suitable for use in continuous production systems such as hollow fibre bioreactors. The utility of the LCR/MEL cell system is demonstrated by the expression of growth hormone at high levels (greater than 100 mg/l) 7 days after induction. Since the expression levels seen do not depend upon gene amplification and are independent of the integration position of the expression cassette, it is possible to obtain clones with stable high-level expression within 3-4 weeks after transfection. 相似文献
3.
Prostatic steroid-binding protein, whose expression is stimulated by androgens, consists of two subunits, one containing the polypeptides C1 and C3 and the other containing the polypeptides C2 and C3. We have isolated and sequenced cDNA clones specific for C3 mRNA and used them to isolate and characterize genomic clones for two C3 genes. Both genes are 3.2 kilobases with identical exon/intron arrangements, which is similar to the organization of the C1 and C2 genes, suggesting that they may have arisen by duplications of an ancestral gene. Finally, homologous human genes have not been detected. 相似文献
4.
Range and magnitude of the steric pressure between bilayers containing phospholipids with covalently attached poly(ethylene glycol). 总被引:4,自引:3,他引:1 下载免费PDF全文
The interactive properties of liposomes containing phospholipids with covalently attached poly(ethylene glycol) (PEG-lipids) are of interest because such liposomes are being developed as drug delivery vehicles and also are ideal model systems for measuring the properties of surface-grafted polymers. For bilayers containing PEG-lipids with PEG molecular weights of 350, 750, 2000, and 5000, pressure-distance relations have been measured by X-ray diffraction analysis of liposomes subjected to known applied osmotic pressures. The distance between apposing bilayers decreased monotonically with increasing applied pressure for each concentration of a given PEG-lipid. Although for bilayers containing PEG-350 and PEG-750 the contribution of electrostatic repulsion to interbilayer interactions was significant, for bilayers containing PEG-2000 and PEG-5000 the major repulsive pressure between bilayers was a steric pressure due to the attached PEG. The range and magnitude of this steric pressure increased both with increasing PEG-lipid concentration and PEG size, and the extension length of the PEG from the bilayer surface at maximum PEG-lipid concentration depended strongly on the size of the PEG, being less than 35 A for PEG-750, and about 65 A for PEG-2000 and 115 A for PEG-5000. The measured pressure-distance relations have been modeled in terms of current theories (deGennes, 1987; Milner et al., 1988b) for the steric pressure produced by surface-grafted polymers, as modified by us to take into account the effects of polymer polydispersity and the possibility that, at low grafting densities, polymers from apposing bilayers surfaces can interpenetrate or interdigitate. No one theoretical scheme is sufficient to account for all the experimental results. However, for a given pressure regime, PEG-lipid size, and PEG-lipid surface density, the appropriately modified theoretical treatment gives a reasonable fit to the pressure-distance data. 相似文献
5.
Structural and functional studies of the endothelial activation antigen endothelial leucocyte adhesion molecule-1 using a panel of monoclonal antibodies. 总被引:14,自引:0,他引:14
R Pigott L A Needham R M Edwards C Walker C Power 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(1):130-135
We have produced a panel of mAb to the endothelial activation Ag endothelial leucocyte adhesion molecule-1 (ELAM-1), using both a conventional immunization protocol and one involving immunosuppression. By constructing ELAM-1 mutants we have demonstrated that seven of these antibodies recognize epitopes within the lectin domain of ELAM-1 and that one binds within the complement regulatory protein domains. These studies also suggest that the EGF-like domain is important in maintaining the conformation of the neighbouring lectin domain. In functional studies, U937 cells bound to Cos cells expressing either ELAM-1 or ELAM-1 with the complement regulatory protein domains deleted. No adhesion was observed to Cos cells expressing ELAM-1 mutants lacking either the lectin or EGF-like domains. The fact that antibodies directed against the lectin domain can inhibit adhesion suggest that this domain is directly involved in cell binding. 相似文献
6.
D. Needham 《Cell biochemistry and biophysics》1991,18(2):99-121
Studies that examine the shear- and abrasion-sensitivity of proliferating cells are important in order to understand the behavior
of hybridoma cells in bioreactor culture and metastasizing cancer cells in the bloodstream. Little is known about the link
between morphology, structure, and mechanical properties of a given cell line, especially with respect to variations throughout
the cell cycle. In our experiments with GAP A3 hybridoma cells, distinct cell morphologies were identified and correlated
with phases of the cell cycle by video microscopic observation of synchronized cells, and of individual cells that were followed
throughout their cell cycle. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (apparent
cell viscosity) properties of single cells. As the cell cycle progressed at 37°C, an increase in cell volume from 1400 μm3 to 5700 μm3 was accompanied by an increase in apparent cell viscosity from 430 poise to 12,000 poise, consistent with an accumulation
of more cytoplasmic material in the “older” cells. Hybridomas are representative of the various leukemias derived from hemopoietic
cells, and even though as a whole, they appeared to be rather shear-insensitive, the wide range of property values demonstrates
that a given cell line cannot be characterized by a single value for any one property, and that properties must be related
to the cell cycle when considering proliferating cells. It is interesting to see if distinct stages in the metastatic sequence
of events might correlate with any of these physical features of the cell cycle, irrespective of cell type or cell line. For
example, the cytokinetic doublet could represent a fragile structure that may fail and produce cell death under fluid-shear
conditions that would not affect the cells at any other stage in the cell cycle. Identifying such cell cycle-dependent features
in metastasizing cancer cells could lead to a better understanding of the metastatic process and to possible clinical treatments
directed at making cells more shear- and abrasion-sensitive, and therefore, more likely to be killed by the natural hydrodynamic
forces of the circulatory system. 相似文献
7.
Prostatic steroid binding protein, whose expression is stimulated by androgens, consists of two subunits: one containing the polypeptides C1 and C3 and the other containing C2 and C3. We have characterised genomic clones containing the C1 and C2 genes by restriction enzyme analysis and DNA sequencing. Both genes are 3.2 Kb, have similar exon/intron arrangements and share considerable DNA sequence homologies in their coding regions, intervening sequences and 5' upstream DNA sequence which suggests that they have probably arisen from the duplication of an ancestral gene. The 5' termini of C1 and C2 mRNA have been mapped; the sequence TATAAA appears 30 nucleotides upstream but a CAAT-like sequence at -60 - -80 is absent. Finally, homologous human genes have not been detected. 相似文献
8.
P. D. Needham R. G. Atkinson B. A. M. Morris R. C. Gardner A. P. Gleave 《Plant cell reports》1998,17(8):631-639
We have constructed a binary vector containing elements of the monopartite geminivirus, tobacco yellow dwarf virus (TYDV).
The vector is designed to be stably integrated into the plant genome, via Agrobacterium-mediated transfer. Upon expression of the viral replication-associated protein the TYDV elements are released from the T-DNA
and then replicate episomally. We refer to these released forms as multicopy plant episomes (MPE). Tobacco plants (Nicotiana tabacum cv `Samsun') transformed with the vector showed MPE release and subsequent episomal replication in 6 of 11 of these plants.
An MPE vector containing the uidA gene faithfully replicated and maintained the reporter gene, even though the construct was considerably larger than the wild-type
TYDV genome. Histochemical staining revealed a speckled GUS expression phenotype which could be correlated with MPE replication.
Received: 11 July 1997 / Revision received: 4 November 1997 / Accepted: 8 December 1997 相似文献
9.
C. O. Solberg H. J. Meuwissen R. N. Needham R. A. Good J. M. Matsen 《BMJ (Clinical research ed.)》1971,1(5739):18-23
In 11 patients receiving transplants of allogeneic bone marrow, the graft was successful in six. Nine patients developed infections, and six died—five of septicaemia and one of Pneumocystis carinii pneumonia. Fifty individual infections occurred. Predisposing factors included severe underlying diseases, long-term exposure to resistant hospital organisms, heavy immunosuppressive therapy, and graft-versus-host disease. Gram-negative bacilli and Candida albicans were the most common causative organisms. In every instance of septicaemia identical organisms were isolated from blood cultures and simultaneously obtained stool cultures. Infection with exogenous organisms often occurred in patients occupying conventional isolation rooms. Isolation of one patient for 45 days in a laminar air flow room prevented infection with exogenous organisms. 相似文献
10.