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1.
Processing of 45 s nucleolar RNA 总被引:29,自引:0,他引:29
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Predation by naturally occurring predatory arthropods was investigated to explain variations in population numbers of twospotted
spider mite (Tetranychus urticae Koch) between first and second season strawberry crops.
Araneomorph spiders. European harvestman [Phalangium opilio (L.)], Tasmanian lacewing [Micromus tasmaniae (Walker)] and Pacific damsel bug [Nabis kinbergii Reuter] were the only predators found in high numbers. However, spiders and harvestment were more prevalent than lacewings
and nabids.
Laboratory feedings trials indicated spiders build horizontal webs in the plants and prey predominantly on small flying insects
that shelter in the crops. Similar feeding trials cofirmed the palatability of TSSM to spiders and harvestmen.
Immunological testing for proteins of TSSM, aphids, Collembola and leafrollers in the intestines of field collected European
harvestman, spiders, Tasmanian lacewing and Pacific damsel bug confirmed European harvestman includes TSSM in its diet, but
not in large enough quantities to exert a significant regulating pressure on TSSM populations. Lacewings and nabids include
TSSM in their diets but only in very small quantities (2% and 1% respectively). Spiders do not take TSSM unless they drop
or spin down onto the spider webbing.
The immunological testing also showed European harvestman to be a polyphagous and opportunistic feeder. Prey residues were
detected more frequently in harvestmen intestines at times of prey abundance which indicated a seasonality to harvestmen diet.
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Epithelial cytoskeletal framework and nuclear matrix-intermediate filament scaffold: three-dimensional organization and protein composition 总被引:60,自引:26,他引:34 下载免费PDF全文
Madin-Darby canine kidney (MDCK) cells grow as differentiated, epithelial colonies that display tissue-like organization. We examined the structural elements underlying the colony morphology in situ using three consecutive extractions that produce well-defined fractions for both microscopy and biochemical analysis. First, soluble proteins and phospholipid were removed with Triton X-100 in a physiological buffer. The resulting skeletal framework retained nuclei, dense cytoplasmic filament networks, intercellular junctional complexes, and apical microvillar structures. Scanning electron microscopy showed that the apical cell morphology is largely unaltered by detergent extraction. Residual desmosomes, as can be seen in thin sections, were also well- preserved. The skeletal framework was visualized in three dimensions as an unembedded whole mount that revealed the filament networks that were masked in Epon-embedded thin sections of the same preparation. The topography of cytoskeletal filaments was relatively constant throughout the epithelial sheet, particularly across intercellular borders. This ordering of epithelial skeletal filaments across contiguous cell boundaries was in sharp contrast to the more independent organization of networks in autonomous cells such as fibroblasts. Further extraction removed the proteins of the salt-labile cytoskeleton and the chromatin as separate fractions, and left the nuclear matrix-intermediate filament (NM-IF) scaffold. The NM-IF contained only 5% of total cellular protein, but whole mount transmission electron microscopy and immunofluorescence showed that this scaffold was organized as in the intact epithelium. Immunoblots demonstrate that vimentin, cytokeratins, desmosomal proteins, and a 52,000-mol-wt nuclear matrix protein were found almost exclusively in the NM-IF scaffold. Vimentin was largely perinuclear while the cytokeratins were localized at the cell borders. The 52,000-mol-wt nuclear matrix protein was confined to the chromatin- depleted matrix and the desmosomal proteins were observed in punctate polygonal arrays at intercellular junctions. The filaments of the NM-IF were seen to be interconnected, via the desmosomes, over the entire epithelial colony. The differentiated epithelial morphology was reflected in both the cytoskeletal framework and the NM-IF scaffold. 相似文献
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Cytochalasin releases mRNA from the cytoskeletal framework and inhibits protein synthesis. 总被引:25,自引:0,他引:25 下载免费PDF全文
Cytochalasin D was shown to be a reversible inhibitor of protein synthesis in HeLa cells. The inhibition was detectable at drug levels typically used to perturb cell structure and increased in a dose-dependent manner. The drug also released mRNA from the cytoskeletal framework in direct proportion to the inhibition of protein synthesis. The released mRNA was unaltered in its translatability as measured in vitro but was no longer translated in the cytochalasin-treated HeLa cells. The residual protein synthesis occurred on polyribosomes that were reduced in amount but displayed a normal sedimentation distribution. The results support the hypothesis that mRNA binding to the cytoskeletal framework is necessary although not sufficient for translation. Analysis of the cytoskeletal framework, which binds the polyribosomes, revealed no alterations in composition or amount of protein as a result of treatment with cytochalasin D. Electron microscopy with embedment-free sections shows the framework in great detail. The micrographs revealed the profound reorganization effected by the drug but did not indicate substantial disaggregation of the cytoskeletal elements. 相似文献
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