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991.
Differential display analysis of gene expression during the induction of mucosal immunity 总被引:1,自引:0,他引:1
One approach to understanding the physiologically relevant events during the induction of an immune response is to identify genes that are expressed when the immune system first encounters antigen. Such an investigation requires a naive but fully functional immune system, and the fetal lamb provides these conditions during the last trimester of gestation. 'Intestinal segments,' containing a jejunal Peyer's patch, were surgically prepared in fetal lambs (>120 days gestation) and individual 'intestinal segments' were injected with either culture medium or infectious bovine rotavirus. Peyer's patch tissue was collected 18 h postinfection. Histology and virus culture confirmed that bovine rotavirus had infected the mucosal epithelium. RNA was extracted from jejunal Peyer's patch tissue and mRNA differential display was used to identify genes expressed following rotavirus infection. Ten cDNAs were identified by differential display and these cDNAs were isolated, cloned, and sequenced. One of the cDNAs sequenced, displayed homology to the gene encoding the sperm surface protein Sp17. Differential expression of this gene in antigen-exposed jejunal Peyer's patches was confirmed by Northern blot and RT-PCR. The complete sequence for sheep Sp17 mRNA was obtained from a lambda cDNA library, prepared from the jejunal Peyer's patch of a young lamb. Sp17 expression was detected by RT-PCR in a variety of mucosa-associated lymphoid tissues but not in primary or other secondary lymphoid tissues. Thus, the fetal lamb model may be appropriate for identifying genes relevant to mucosal immunity. 相似文献
992.
We study the dynamics and stability of legged locomotion in the horizontal plane. Motivated by experimental studies of insects,
we develop two- and three-degree-of freedom rigid body models with pairs of ‘virtual’ elastic legs in intermittent contact
with the ground. We focus on conservative compliant-legged models, but we also consider prescribed forces, prescribed leg
displacements, and combined strategies. The resulting mechanical systems exhibit periodic gaits whose stability characteristics
are due to intermittent foot contact, and are largely determined by geometrical criteria. Most strikingly, we show that mechanics
alone can confer asymptotic stability in heading and body orientation. In a companion paper, we apply our results to rapidly
running cockroaches.
Received: 6 September 1999 / Accepted in revised form: 8 May 2000 相似文献
993.
Identification of methyl farnesoate in the cypris larva of the barnacle, Balanus amphitrite, and its role as a juvenile hormone 总被引:1,自引:0,他引:1
Smith PA Clare AS Rees HH Prescott MC Wainwright G Thorndyke MC 《Insect biochemistry and molecular biology》2000,30(8-9):885-890
Previous investigations have shown that insect juvenile hormone (JH) and its analogues induce precocious metamorphosis of barnacle cypris larvae. In the present study, methyl farnesoate (MF; structurally identical to JH III, except for the absence of an epoxide group) has been shown to have a concentration-dependent effect on the development of cyprids of the barnacle Balanus amphitrite. Analysis of cypris extracts by gas chromatography-mass spectrometry with selected ion monitoring (GC-MS-SIM) confirmed the presence of endogenous MF. These data provide evidence that MF functions as a juvenilizing hormone in barnacle cyprids, an effect that hitherto has not been noted. 相似文献
994.
Victoria Blue BO (VBBO) is thought to exert its photocytotoxic effects via free radical generation. Glutathione and related enzymes are associated with the protection of normal tissues against free-radical damage and have also been implicated in multiple drug resistance. It might, therefore, be expected that cells containing higher levels of glutathione would be resistant to the cytotoxic effects of VBBO. The total glutathione content for a murine mammary tumour cell line, EMT6-S, was found to be lower than in a multi-drug resistant cell line, EMT6-R, 21.84+/-2.54 microg (mg protein)(-1) and 18.79+/-2.7 microg (mg protein)(-1), respectively; however, this was not found to be a significant difference (p > 0.05, Student t-test). Buthionine sulfoximine, a potent inhibitor of gamma-glutamyl cysteine synthetase, brought about a reduction in glutathione levels in both EMT6-S and EMT6-R cell lines in a concentration-dependent manner. Buthionine sulfoximine administration was effective in reducing intracellular glutathione levels by up to 90% in both types of cells. Interestingly, glutathione depletion of EMT6-S and EMT6-R cells did not enhance the photocytotoxic effect of VBBO, suggesting that the primary site of action of VBBO may be at an intracellular site not protected by glutathione or that the mechanism of action is not via the in situ generation of free radical species. 相似文献
995.
deMello DE Mahmoud S Padfield PJ Hoffmann JW 《In vitro cellular & developmental biology. Animal》2000,36(6):374-382
Summary This paper describes a new fully differentiated Type-II alveolar epithelial cell line designated T7, derived from transgenic H-2Kb-tsA58 mice, capable of being passaged as an immortalized cloned cell line in culture. H-2Kb-tsA58 mice harbor a temperature-sensitive (ts) mutant of the simian virus 40 (SV40) large tumor antigen (T antigen) under
the control of the γ-interferon (INF)-inducible mouse major histocompatibility complex H-2Kb promoter. When cultured under permissive conditions (33°C and in the presence of γ-INF) cells isolated from H-2Kb-tsA58 mice express the large T antigen, which drives the cells to proliferate. However, upon withdrawal of the γ-INF and
transfer of the cells to a higher temperature (39°C), T antigen expression is turned off, the cells stop proliferating and
differentiate. The T7 cell line is a clonal cell line originally derived from a Type-II cell-rich fraction isolated from lungs of H-2Kb-tsA58 mice. The T7 cells form confluent monolayers, and have a polarized epithelial cell morphology with tight junctions and apical microvilli.
In addition, the T7 cells have distinct cytoplasmic lamellar bodies, which become more numerous and pronounced when the cells are grown under
nonpermissive conditions. The T7 cells synthesize and secrete phosphatidylcholine and the three surfactant proteins, SP-A, SP-B, and SP-C. The T7 cell line is unique in that it is the first non-tumor-derived Type-II cell line capable of synthesizing and secreting the
major components of surfactant. Based on the criteria studied, the T7 cell line is phenotypically very similar to normal Type-II cells. The T7 cell line, therefore, should prove a valuable experimental system to advance the study of the cell biology/physiology of
surfactant metabolism and secretion as well as serve as a model for other studies of Type-II cell physiology. 相似文献
996.
The hammerhead ribozyme is able to cleave RNA in a sequence-specific manner. These ribozymes are usually designed with four
basepairs in helix II, and with equal numbers of nucleotides in the 5′ and 3′ hybridizing arms that bind the RNA substrate
on either side of the cleavage site. Here guidelines are given for redesigning the ribozyme so that it is small, but retains
efficient cleavage activity. First, the ribozyme may be reduced in size by shortening the 5′ arm of the ribozyme to five or
six nucleotides; for these ribozymes, cleavage of short substrates is maximal. Second, the internal double-helix of the ribozyme
(helix II) may be shortened to one or no basepairs, forming a miniribozyme or minizyme, respectively. The sequence of the
shortened helix+loop II greatly affects cleavage rates. With eight or more nucleotides in both the 5′ and the 3′ arms of a
miniribozyme containing an optimized sequence for helix+loop II, cleavage rates of short substrates are greater than for analogous
ribozymes possessing a longer helix II. Cleavage of genelength RNA substrates may be best achieved by miniribozymes. 相似文献
997.
Because the H2O2 and O2
− generated during a pathogen-triggered oxidative burst could either protect or destroy a besieged plant cell, their synthesis
might be expected to be tightly regulated. We have examined the nature of this regulation as it is communicated between homologous
and heterologous oxidative-burst pathways, using both chemical (oligogalacturonic acid, harpin, fensulfothion) and mechanical
(osmotic stress) stimuli to induce the burst. We report here that the above three chemical elicitors attenuate a subsequent
oxidative burst induced in cultured soybean (Glycine max L.) cells by either the same (homologous desensitization) or a different chemical elicitor (heterologous desensitization).
Further, when the magnitude of the initial oxidative burst is maximal, the cells remain refractory to subsequent elicitation
for at least 10 min and then revive their sensitivities to re-stimulation with a half-time of >20 min. Mechanical stimulation
of the oxidative burst appears to be regulated by a different set of constraints. Although initiation of a mechanically induced
burst leads to attenuation of a subsequent mechanically induced burst, the same mechanical stimulus is peculiarly unable to
reduce a subsequent chemically induced burst. The converse is also true, suggesting that heterologous desensitization of the
oxidative burst does not extend to mixed chemical and mechanical/osmotic stimuli. However, communication between these disparate
forms of elicitation is still demonstrated to occur, since low-level chemical stimuli strongly synergize concurrent low-level
osmotic stimuli and vice versa. Furthermore, the pattern of synergy changes dramatically if one stimulus is administered immediately
prior to the other. Taken together, these data demonstrate that significant cross-talk occurs among the different signaling
pathways of the oxidative burst and that the overall process is tightly regulated.
Received: 10 January 2000 / Accepted: 22 February 2000 相似文献
998.
Photosynthesis in the green alga Dunaliella tertiolecta, as measured by chlorophyll fluorescence, is inhibited by ultraviolet radiation and specifically, under the conditions used,
by UVB radiation (UVBR). The decline in the fluorescence parameters Fv/Fm and ΔF/Fm' under constant UVBR is a first-order function of time of exposure. The data are well-described by the Kok (1956) model, which
assumes a dynamic interaction between damage and repair, with repair being proportional to the pool size of inactivated targets.
The pattern of photoinhibition is also consistent with the Kok model, in that it shows an initial, approximately linear phase
which is time-dependent (reciprocity holds), a transition phase and then an asymptotic phase, representing an equilibrium
between damage and repair, which is determined by UVBR fluence rate (reciprocity fails). Photoinhibition in the presence of
lincomycin, a protein synthesis inhibitor, is consistent with the cessation of repair processes and, under these conditions,
photoinhibition is proportional to exposure time.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
999.
Extended Survival and Persistence of Campylobacter spp. in Water and Aquatic Biofilms and Their Detection by Immunofluorescent-Antibody and -rRNA Staining 总被引:4,自引:0,他引:4
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Clive M. Buswell Yvonne M. Herlihy Lorna M. Lawrence James T. M. McGuiggan Philip D. Marsh C. William Keevil Steve A. Leach 《Applied microbiology》1998,64(2):733-741
In water microcosm experiments, the survival times of Campylobacter isolates differed by up to twofold, as determined by culturing; this difference increased to fourfold when particular combinations of temperature and oxygenation were used. The mean survival times were much longer at 4 and 10°C (202 and 176 h, respectively) than at 22 and 37°C (43 and 22 h, respectively). The influence of anaerobiosis on survival time was less dramatic and differed considerably between isolates. In a two-stage water distribution model preparation containing a biofilm consisting of standardized autochthonous water microflora, Campylobacter isolates continued to differ in survival time. However, the survival times of cultures were considerably longer in the presence of the autochthonous water microflora (strains CH1 and 9752 survived 700 and 360 h, respectively, at 4°C) than in the sterile microcosms (strains CH1 and 9752 survived 230 and 157 h, respectively). Although increased temperature and oxygenation were generally detrimental to culturability, the interaction of these two factors influenced the two strains examined differently. When the organisms were grown aerobically at 30°C, the survival of the two strains was reversed; aerobiosis decreased the survival time of strain CH1 by 30%, but unexpectedly improved the persistence time of strain 9752 by more than threefold. Persistence times within biofilms were much longer when they were determined by detection methods not involving culturing. Immunofluorescent-antibody staining demonstrated that the pathogen persisted up to the termination of the experiments after 28 and 42 days of incubation at 30 and 4°C, respectively. The specificity of detection within intact biofilms was reduced because of high background fluorescence. However, preliminary studies with a Campylobacter-specific rRNA probe revealed the same extended persistence of the pathogen within the biofilms. 相似文献
1000.
Richard E. Lenski Judith A. Mongold Paul D. Sniegowski Michael Travisano Farida Vasi Philip J. Gerrish Thomas M. Schmidt 《Antonie van Leeuwenhoek》1998,73(1):35-47
An important problem in microbial ecology is to identify those phenotypic attributes that are responsible for competitive fitness in a particular environment. Thousands of papers have been published on the physiology, biochemistry, and molecular genetics of Escherichia coli and other bacterial models. Nonetheless, little is known about what makes one genotype a better competitor than another even in such well studied systems. Here, we review experiments to identify the phenotypic bases of improved competitive fitness in twelve E. coli populations that evolved for thousands of generations in a defined environment, in which glucose was the limiting substrate. After 10000 generations, the average fitness of the derived genotypes had increased by 50% relative to the ancestor, based on competition experiments using marked strains in the same environment. The growth kinetics of the ancestral and derived genotypes showed that the latter have a shorter lag phase upon transfer into fresh medium and a higher maximum growth rate. Competition experiments were also performed in environments where other substrates were substituted for glucose. The derived genotypes are generally more fit in competition for those substrates that use the same mechanism of transport as glucose, which suggests that enhanced transport was an important target of natural selection in the evolutionary environment. All of the derived genotypes produce much larger cells than does the ancestor, even when both types are forced to grow at the same rate. Some, but not all, of the derived genotypes also have greatly elevated mutation rates. Efforts are now underway to identify the genetic changes that underlie those phenotypic changes, especially substrate specificity and elevated mutation rate, for which there are good candidate loci. Identification and subsequent manipulation of these genes may provide new insights into the reproducibility of adaptive evolution, the importance of co-adapted gene complexes, and the extent to which distinct phenotypes (e.g., substrate specificity and cell size) are affected by the same mutations. 相似文献