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At least 613 records · Page 34Linked to original sources
PubMed1989

Effect of cytochalasin D on cell morphology and AcMNPV replication in a Spodoptera frugiperda cell line.

Cytochalasin D (CD) is a specific inhibitor of actin microfilament elongation and has been used to identify actin-dependent cellular processes. In this study we observed the effects of this inhibitor on Autographa californica M nuclear polyhedrosis virus infected and uninfected IPLB-SF-21 cells by electron microscopy. The cytochalasin D-induced morphological effects detected in uninfected cells included lobulate nuclei, double nuclei, long retraction processes, increased zeiosis, more frequent plasma membrane indentations, increased vacuolation, more numerous coated pits and vesicles, filamentous masses in the cytoplasm, and decreased surface microvilli. Observation of infected cells treated with CD revealed that viral morphogenesis was severely affected. Few normal-appearing nucleocapsids were seen in the nucleus, and none were detected in the cytoplasm. Instead, long capsid-like tubular structures appeared juxtaposed to the inner nuclear membrane. Very infrequently sections of these structures contained electron dense material. The center of the nucleus contained electron-dense, spidery-like structures, presumably viral DNA. Normal virus was not observed to bud from the plasma membrane but electron-lucent, coreless-particles were. By 50 hr postinfection occasional polyhedra appeared, but these contained few or no enveloped virions. The intranuclear fibrous masses normally associated with infection were significantly reduced. These observations suggest that viral morphogenesis, especially nucleocapsid assembly, is an actin-dependent process.

Animals↗
PubMed1990

Bacillus thuringiensis potency bioassays against Heliothis armigera, Earias insulana, and Spodoptera littoralis larvae based on standardized diets.

Bacillus thuringiensis screening programs based on the official potency bioassay using third-instar larvae and on a neonate bioassay were developed for Heliothis armigera, Earias insulana, and Spondoptera littoralis. In these bioassays, the diets were standardized to be suitable, with minor modifications, for feeding of the three lepidopterans. The bioassay protocol was based on determination of the LC50 of the microbial standard HD-1-S-80 in the insects susceptible to B. thuringiensis var. kurstaki strains. This was followed by preliminary screening of B. thuringiensis strains at the LC50 of the B. thuringiensis standard. The B. thuringiensis strains causing 100% mortality at this LC50 in the larvae were selected for potency determinations. The neonate bioassay was suitable for accurate determinations of potencies also in S. littoralis--a representative of insects weakly susceptible to the HD-1 standard. The role of the official and the neonate bioassays in developing microbial control programs is discussed.

Animals↗
PubMed1994

Spodoptera frugiperda Sf-9 cells nuclear factor binds to a specific sequence on the baculovirus polyhedrin promoter.

The promoter of the baculovirus polyhedrin gene is used for the heterologous expression of proteins in the baculovirus expression system. The polyhedrin gene of baculovirus is a very late gene that is hyper-expressed 18-24 h post-infection (P.I). We analyzed the DNA-binding activity of the polyhedrin promoter using gel mobility shift analysis, DNaseI footprint analysis and UV cross-linking experiments. Specific DNA-binding activity was found in uninfected cells. Specific binding activity was also found in cells during the early stage of viral infection and it decreased 18-24 h P.I. The DNA-binding activity localized to positions -72 to -86 on the polyhedrin promoter relative to the initial ATG. The molecular mass of the protein interacting with the DNA was in the range of 200 kDa. The data implies the presence of a host-encoded DNA-binding protein that acts as a negative regulator and is involved in the delayed expression of polyhedrin. In an initial attempt to test this hypothesis, transient cotransfection assays were performed in infected cells. These experiments were designed to assess the in vivo competition of proteins that interact with the polyhedrin promoter. The results support the concept of negative regulation. Thus it is possible that baculovirus utilizes an insect cell-derived nuclear factor to control the differential expression of late versus very late genes. A model that can account for our observations is discussed.

Animals↗