Isolation and characterization of cycloheximide-resistant mosquito cell clones

Synchronization of Aedes albopictus mosquito cells using hydroxyurea

We have established conditions for use of hydroxyurea, a reversible inhibitor of DNA synthesis, to synchronize the division cycle of a continuous cell line from the mosquito, Aedes albopictus. In the range of 0.15-0.25 mM hydroxyurea, an 18 h treatment, followed by removal of the drug, results in effective synchronization. When combined with the partial synchronization that occurs within 10 h of dilution and plating, more than 80% of cells treated with hydroxyurea could be recovered in the synthesis (S) phase of the cell cycle during the 4 h period after removal of the drug. The degree of synchrony was enhanced when cells were exposed to two consecutive hydroxyurea treatments spaced 10 h apart. Synchronized cells expressed maximal levels of a reporter gene when transfected immediately after removal of hydroxyurea. This is the first description of effective chemical synchronization of an insect cell line using hydroxyurea.

Thymidine kinase-deficient mutants of Aedes albopictus mosquito cells

Aedes albopictus mosquito cells resistant to the thymidine analog 5-bromodeoxyuridine (BrdU) were obtained using a single-step selection procedure. The resistant cells were characterized with respect to growth in the presence of BrdU, incorporation of [3H]uridine and [3H]thymidine, and thymidine kinase activity in crude extracts. The LC50 for TK-6 cells was 95 micrograms BrdU/ml, and for TK-8 cells was 45 micrograms/ml. Both clones incorporated [3H]uridine at levels corresponding to those in wild-type cells. TK-6 and TK-8 cells did not incorporate [3H]thymidine into acid-precipitable material, nor did they contain measurable thymidine kinase activity. Thymidine kinase activity in crude extracts from wild-type cells had a Km of 2 microM and a Vmax of 10 pmol.min-1.mg-1 protein.

Cell-free translation in lysates from Spodoptera frugiperda (Lepidoptera: Noctuidae) cells

1. Conditions for in vitro translation of mRNA in cell-free extracts from cultured Spodoptera frugiperda cells were defined. 2. Incorporation of [35S]methionine into acid-precipitable material increased for approximately 1 hr, and was sensitive to the protein synthesis inhibitors pactamycin and cycloheximide. 3. Micrococcal nuclease-treated lysate, primed with purified rabbit globin mRNA, synthesized a major protein with the size of full length globin, indicating that the lysate supported correct initiation and elongation of polypeptides.

Pleiotropic changes in cycloheximide-resistant insect cell clones

Somatic cell mutants resistant to drugs that interact with the eukaryotic ribosome provide a useful tool for studies on ribosome structure, function, and genetics. From Aedes albopictus (mosquito) cells, cycloheximide-resistant mutants (Cx-705 and Cx-738) that were about 30-fold more resistant to cycloheximide than the parental cells have been obtained. The observation that protein synthesis in cell-free lysates from Cx-705 and Cx-738 cells was resistant to cycloheximide led us to suspect that the alteration in these mutants might affect the ribosome. The present studies show that the cycloheximide-resistant cells grow poorly and eventually die at 34.5 degrees C, a temperature at which wild-type cells grow normally. Relative to control cells, the cycloheximide-resistant cells show increased sensitivity to G-418, another antibiotic that interacts with the eukaryotic ribosome. However, there were no differences between cycloheximide-resistant cells and wild-type cells in sensitivity to puromycin, emetine, or cryptopleurine. Cx-705 cells were predominantly diploid; in contrast, the frequency of tetraploid nuclei in Cx-738 cells was about 40%.

Characterization of the ribosomal proteins from mosquito (Aedes albopictus) cells

Proteins from the large and small subunits of Aedes albopictus (mosquito) cytoplasmic ribosomes were characterized by two-dimensional polyacrylamide gel electrophoresis. The small subunit contained 28-31 proteins ranging in molecular mass from 10 to 49 kDa. The large subunit contained 36-39 proteins that ranged in molecular mass from 11 to 53 kDa. The largest protein on the small subunit, S1, was the predominant phosphorylated ribosomal protein. Under long-term labelling conditions, L4 and L33 were also phosphorylated. Peptide mapping by partial proteolysis indicated that Ae. albopictus S1 may share partial amino acid homology with the phosphorylated ribosomal protein S6 from Drosophila melanogaster. Unlike Drosophila S6, however, Aedes S1 was not dephosphorylated during heat shock. Treatment of mosquito cells with the insect molting hormone 20-hydroxyecdysone did not affect phosphorylation of ribosomal proteins.

Induction and selection of drug resistant mutants of Plasmodium falciparum

Conditions for mutagenizing Plasmodium falciparum in culture with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine have been established. Parasite mutants resistant to aphidicolin, cycloheximide and sinefungin have been selected and subcloned.