The obligate intracellular microbe, Wolbachia pipientis (Rickettsiales; Anaplasmataceae), is a Gr... more The obligate intracellular microbe, Wolbachia pipientis (Rickettsiales; Anaplasmataceae), is a Gram-negative member of the alpha proteobacteria that infects arthropods and filarial worms. Although closely related to the genera Anaplasma and Ehrlichia, which include pathogens of humans, Wolbachia is uniquely associated with invertebrate hosts in the clade Ecdysozoa. Originally described in Culex pipiens mosquitoes, Wolbachia is currently represented by 17 supergroups and is believed to occur in half of all insect species. In mosquitoes, Wolbachia acts as a gene drive agent, with the potential to modify vector populations; in filarial worms, Wolbachia functions as a symbiont, and is a target for drug therapy. A small number of Wolbachia strains from supergroups A, B, and F have been maintained in insect cell lines, which are thought to provide a more permissive environment than the natural host. When transferred back to an insect host, Wolbachia produced in cultured cells are infectio...
In Vitro Cellular & Developmental Biology - Animal, 2018
Wolbachia pipientis (Rickettsiales; Anaplasmataceae) is an obligate intracellular alpha proteobac... more Wolbachia pipientis (Rickettsiales; Anaplasmataceae) is an obligate intracellular alpha proteobacterium that occurs in arthropods and filarial worms. Some strains of Wolbachia can be maintained as persistent infections in insect cell lines. C/wStr1 cells from the mosquito Aedes albopictus maintain a robust infection with Wolbachia strain wStr, originally isolated from the planthopper, Laodelphax striatellus. To explore possible functions of penicillin-binding proteins expressed from the wStr genome, C/wStr1 cells were exposed to ampicillin. Absolute levels of Wolbachia increased 3.5-fold in ampicillin-treated cells and fivefold in naive cells newly infected with wStr. Because cell numbers were depressed by ampicillin treatment, Wolbachia yield on a per-cell basis increased by 15-fold. The absence of a similar effect on wAlbB in Aa23 host cells suggests that the Wolbachia strain, the presence/absence of genes encoding penicillin-binding proteins, or the interaction between wAlbB and its host cells may modulate the effects of ampicillin.
In Vitro Cellular & Developmental Biology - Animal, 2019
Factors that influence establishment of Wolbachia, an obligate intracellular bacterium, in novel ... more Factors that influence establishment of Wolbachia, an obligate intracellular bacterium, in novel insect hosts or uninfected insect cell lines are poorly understood. Infectivity of Wolbachia strain wStr was correlated with flow cytometric profiles to define optimal conditions for harvesting an infectious inoculum. Wolbachia recovered from the cell culture supernatant after gentle pipetting of infected cells represented about 1% of the total bacterial population and were more infectious than Wolbachia that remained associated with intact cells and/or membranes after low-speed centrifugation. Optimal establishment of a robust infection in naïve cells required 6 d, at a ratio of 80 to 160 bacteria per cell. Among Aedes albopictus mosquito cell lines, an aneuploid line with a 4n + 1 karyotype was more susceptible to infection than diploid lines. These findings contribute to the in vitro manipulation of Wolbachia, illustrate some of the many factors that influence infectivity, and identify areas for future investigation.
Treatment with tetracycline or rifampicin to eliminate the obligate intracellular bacterium, Wolb... more Treatment with tetracycline or rifampicin to eliminate the obligate intracellular bacterium, Wolbachia pipientis, provides an important tool for validating Wolbachia’s diverse effects on arthropod reproduction, including cytoplasmic incompatibility, feminization, male killing and parthenogenesis. For the soil collembolan, Folsomia candida (Entomobryomorpha: Isotomidae) efforts to establish the role of Wolbachia in parthenogenesis using tetracycline have been ambiguous, possibly reflecting variation in overall experimental design, mode of antibiotic application and duration of treatment. By maintaining F. candida populations on agar plates containing dissolved antibiotics we show that the EC50 (effective concentration for 50% reduction in biomass) for tetracycline is 50-fold higher than for rifampicin. Experiments with the fluorescent dye rhodamine further show that tetracycline deters feeding. Using individual Collembola, we show that reproductively mature F. candida survive more than 60 days exposure to tetracycline at concentrations 4-fold higher than the EC50 and that its effect on egg production is reversible, consistent with persistence of Wolbachia during tetracycline treatment. As has been shown with other microbes, our results suggest that in F. candida, Wolbachia survives antibiotic exposure by entering a metabolically dormant persister state, from which it can recover under favorable conditions. This possibility is of particular interest because persister cells are induced by toxin-antitoxin (TA) gene pairs, which have recently been associated with Wolbachia-induced cytoplasmic incompatibility in Culex pipiens mosquitoes.
The American Journal of Tropical Medicine and Hygiene, 2001
We have used two-dimensional polyacrylamide gel electrophoresis to examine changes in the relativ... more We have used two-dimensional polyacrylamide gel electrophoresis to examine changes in the relative abundance and diversity of non-secreted proteins in Aedes aegypti fat body preparations during a reproductive cycle. Electrophoretic profiles were evaluated at four time points after eclosion, and at five time points after a blood meal. In contrast to the dramatic changes in abundance of specific secreted proteins such as vitellogenin, our results show that the complement of proteins internal to the fat body remains relatively constant during the mosquito reproductive cycle. Of the approximately 5-10% of proteins that do change in abundance, the majority undergo a dramatic decrease within 24 hours after eclosion.
In Vitro Cellular & Developmental Biology - Animal, 2015
The plant allelochemical L-mimosine (β-[N-(3-hydroxy-4-pyridone)]-α-aminopropionic acid; leucenol... more The plant allelochemical L-mimosine (β-[N-(3-hydroxy-4-pyridone)]-α-aminopropionic acid; leucenol) resembles the nonessential amino acid, tyrosine. Because the obligate intracellular alphaproteobacterium, Wolbachia pipientis, metabolizes amino acids derived from host cells, the effects of mimosine on infected and uninfected mosquito cells were investigated. The EC 50 for mimosine was 6-7 μM with Aedes albopictus C7-10 and C/wStr cell lines, and was not influenced by infection status. Mosquito cells responded to concentrations of mimosine substantially lower than those used to synchronize the mammalian cell cycle; at concentrations of 30-35 μM, mimosine reversibly arrested the mosquito cell cycle at the G1/S boundary and inhibited growth of Wolbachia strain wStr. Although lower concentrations of mimosine slightly increased wStr abundance, concentrations that suppressed the cell cycle reduced Wolbachia levels.
In Vitro Cellular & Developmental Biology - Animal, 2015
Wolbachia pipientis (Rickettsiales), an obligate intracellular alphaproteobacterium in insects, m... more Wolbachia pipientis (Rickettsiales), an obligate intracellular alphaproteobacterium in insects, manipulates host reproduction to maximize invasion of uninfected insect populations. Modification of host population structure has potential applications for control of pest species, particularly if Wolbachia can be maintained, manipulated, and genetically engineered in vitro. Although Wolbachia maintains an obligate mutualism with genome stability in nematodes, arthropods can be co-infected with distinct Wolbachia strains, and horizontal gene transfer between strains is potentially mediated by WO phages encoded within Wolbachia genomes. Proteomic analysis of a robust, persistent infection of a mosquito cell line with wStr from the planthopper, Laodelphax striatellus, revealed expression of a full array of WO phage genes, as well as nine of ten non-phage genes that occur between two distinct clusters of WOMelB genes in the genome of wMel, which infects Drosophila melanogaster. These nonphage genes encode potential host-adaptive proteins and are expressed in wStr at higher levels than phage structural proteins. A subset of seven of the non-phage genes is flanked by highly conserved non-coding sequences, including a putative promoter element, that are not present in a syntenically arranged array of homologs in plasmids from three tickassociated Rickettsia spp. These studies expand our understanding of wStr in a host cell line derived from the mosquito, Aedes albopictus, and provide a basis for investigating conditions that favor the lytic phase of the WO phage life cycle and recovery of infectious phage particles.
A family of nine recombinant bacteriophages containing rRNA genes from cultured cells of the mosq... more A family of nine recombinant bacteriophages containing rRNA genes from cultured cells of the mosquito, Aedes albopietus, has been characterized by restriction mapping, Southern-blotting and Sl-nuclease analyses. The 18S rRNA coding region measured 1800 bp and contained a conserved EcoRI site near the Tend. The 28S rRNA coding region was divided into ,, and fl sequences, comprising 1750 and 2000 bp, respectively, which were separated by a 350 bp sequence that is removed from the rRNA precursor during processing. The entire rDNA repeat unit had a minimum length of 15.6 kb, including a nontranscribed spacer region that contained a series of PvuI repeats upstream of the 18S rRNA coding sequence. During development of the mosquito, Aedes aegypti, the rRNA gene copy number per haploid genome increased from about 400 in larvae to about 1200 in adults.
Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 1986
In the mosquito Aedes aegypti, quantitative and qualitative changes have been detected in ribonuc... more In the mosquito Aedes aegypti, quantitative and qualitative changes have been detected in ribonuclease activity during development. 2. Ribonuclease activity is particularly high in extracts from larvae, relative to that in extracts from pupae or adults. 3. Larval extract is enriched for a ribonuclease that is heat-labile, has an alkaline pH optimum, and is extremely sensitive to the divalent cation, manganese. 4. Extract from adult females is enriched for a heat-stable component that has an acidic pH optimum and is more active at 56 than at 30°C. 5. Throughout the vitellogenic cycle, no major changes in ribonuclease activity were detected in fat body extracts.
Wolbachia is an obligate intracellular bacterium (Anaplasmataceae, Rickettisales) that occurs in ... more Wolbachia is an obligate intracellular bacterium (Anaplasmataceae, Rickettisales) that occurs in arthropods and filarial worms, and spreads by vertical transmission in the oocyte cytoplasm. In insects, reproductive distortions associated with Wolbachia, such as cytoplasmic incompatibility in mosquitoes, have potential value for controlling pests, including species that transmit human, animal and plant diseases. Wolbachia strains that propagate as a persistent infection in insect cell lines provide an important resource for developing the genetic tools that will facilitate these applications. Here I describe conditions for flow cytometric evaluation of Wolbachia growth in persistently infected mosquito cells. Cytometry parameters were established using uninfected mosquito cells and Escherichia coli as a surrogate for Wolbachia, and quantitation was correlated with cell counts determined with a Coulter electronic cell counter and bacterial counts based on optical density. The protocol was validated by showing depletion of Wolbachia in medium containing tetracycline and rifampicin, and sensitivity of Wolbachia to treatment of host cells with paraquat, an oxidizing agent, and lumiflavin, an inhibitor of riboflavin uptake. The Wolbachia peak on the flow cytometry histogram was shown to contain Wolbachia by DNA analysis using the polymerase chain reaction, and by infection of naive recipient cells. This approach will streamline investigation of Wolbachia growth in insect cell lines and facilitate identification of culture conditions that select for Wolbachia-infected cells.
We examined survival, growth and protein synthesis in mosquito cells that had been maintained for... more We examined survival, growth and protein synthesis in mosquito cells that had been maintained for up to 21 days in serum-free medium. On polyacrylamide gels, protein bands from "starved" cells remained discrete, and despite low levels of incorporation, radiolabeled bands were detectable, suggesting that low levels of protein synthesis were sustained. A prominent band that accumulated in serum-starved cells was digested with trypsin and analyzed by tandem mass spectrometry, which identified the protein as eukaryotic elongation factor (EF)-1α EF-1α is well-conserved among species, and differential accumulation of EF-1α in serumstarved cells was verified by western blotting using a primary antibody to the homologous protein from Trypanosoma brucei. Aside from its importance in the elongation step of protein synthesis, EF-1α has been shown to have a number of non-canonical functions, including interaction with viral RNA and a potential role in apoptosis. We anticipate that the prolonged viability of mosquito cells in serum-free medium may provide a system to explore whether EF-1α accumulation is an adaptive response compatible with resumption of growth in the event that nutrients are replenished, or whether the excess EF-1α represents an irreversible commitment to an apoptotic pathway.
Somatic cell mutants resistant to drugs that interact with the eukaryotic ribosome provide a usef... more 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%.
In Vitro Cellular & Developmental Biology - Animal, 2008
The Aedes albopictus Aa23 cell line, which is persistently infected with Wolbachia pipientis stra... more The Aedes albopictus Aa23 cell line, which is persistently infected with Wolbachia pipientis strain wAlbB, tends to grow as aggregated clusters of cells that are difficult to disperse for conventional quantification based on cell number. We used A. albopictus C7-10 cells to validate conversion of methylthiazole tetrazolium (MTT) to a colored formazan product with respect to incubation time, cell number over a 40-fold range, and metabolic activity as cells enter stationary phase. Using this assay, we showed that the doubling time of Aa23 cells increases from about 45 h early after plating to more than 70 h as the cells reach stationary levels. Growth of Aa23 cells proceeds at similar rates in the presence or absence of tetracycline concentrations that decrease the abundance of Wolbachia. Insofar as the MTT assay reflects mitochondrial function, our results indicate that, in Aa23 cells, abundance of intracellular Wolbachia has no measurable effect on mitochondrial activity in the presence of tetracycline.
In Vitro Cellular & Developmental Biology - Animal, 2008
In vitro production of the obligate intracellular bacterium, Wolbachia pipientis, is essential to... more In vitro production of the obligate intracellular bacterium, Wolbachia pipientis, is essential to its manipulation as a genetic tool to spread transgenes within vector populations. We have adapted the Wolbachia-infected Aa23 Aedes albopictus mosquito cell line to Eagle's minimal medium, supplemented with nonessential amino acids, glutamine, and 20% fetal bovine serum. When plated at low densities, Aa23E cells grew as patchy monolayers, comprised of non-contiguous clusters of cells that gave rise to solid clumps of tightly adherent cells. Multicellular clumps eventually detached from the substrate and floated freely in the medium. Removal of Wolbachia by treatment with tetracycline did not alter the cytological properties of the host cells, which had a population doubling time of 4-5 d. The presence of Wolbachia was monitored by Giemsa staining of cytological preparations, polymerase chain reaction (PCR) amplification of Wolbachia 16S ribosomal DNA, and by simultaneous PCR amplification of ribosomal protein genes from Wolbachia and mosquito host cell genomes. Wolbachia morphology was pleomorphic, and Wolbachia DNA persisted in the culture medium for several weeks after degradation of PCR-amplifiable host cell DNA.
In Vitro Cellular & Developmental Biology - Animal, 2009
We used Wolbachia pipientis strain wAlbB from Aedes albopictus Aa23 cells to infect clonal Ae. al... more We used Wolbachia pipientis strain wAlbB from Aedes albopictus Aa23 cells to infect clonal Ae. albopictus TK-6 cells, which are resistant to 5-bromodeoxyuridine. Infected TK-6 cells were cultured in medium containing 5-bromodeoxyuridine to select against Aa23 cells that might have persisted in the inoculum. Infected TK-6 lines retained the Wolbachia infection for 5 mo, indicating that their metabolic processes support Wolbachia growth and multiplication. To investigate early events after Wolbachia infection, we labeled infected cells with 35 S[methionine/cysteine]. Patterns of labeled proteins on sodium dodecyl sulfate gels were similar in control and infected cells, with the exception of a 29-kDa protein. Tandem mass spectrometry revealed that the 29-kDa band included α and β subunits of the 26S proteasome. Independent confirmation of the up-regulation of the proteasome was established by probing Western blots with a monoclonal antibody to the proteasome-associated co-factor, ubiquitin. Wolbachia's loss of metabolic pathways for the synthesis of most amino acids and retention of pathways for their uptake and metabolism suggest that proteasome activation provides a mechanism whereby controlled degradation of intracellular host proteins would increase availability of amino acids to support establishment and maintenance of the Wolbachia infection.
We have characterized full-length cDNAs encoding three isoforms of the antibiotic cecropin secret... more We have characterized full-length cDNAs encoding three isoforms of the antibiotic cecropin secreted by the C7^10 cell line from the mosquito, Aedes albopictus. The existence of two cecropin isoforms that differed from the previously described AalCecA was predicted by mass spectrometry and amino acid sequence analysis of peptides that eluted from reversed phase high performance liquid chromatography as a single peak just behind the previously described cecropin, AalCecA. Based on the amino acid sequence of the mature AalCecA peptide, we designed primers that amplified partial cDNAs encoding three different A. albopictus cecropins in reverse transcriptase polymerase chain reactions. Rapid amplification of cDNA ends was then used to complete the cDNA sequences of AalCecA, AalCecB and AalCecC, respectively. Each cDNA encoded a translation product containing a signal peptide, a pro region, and a mature cecropin peptide consistent with amino acid sequence data from chymotryptic digests. Although the mosquito cecropins shared 70^86% identity among each other, they shared only V V40% identity to cecropins from Drosophila melanogaster. Each of the cecropins was expressed within 2 to 4 h after induction, and transcripts measuring 0.3 to 0.5 kb continued to accumulate over 24 h. The three cecropins were secreted in roughly equimolar proportions, and 30 to 90% of AalCecB was amidated at the terminal glycine residue. In contrast, amidated forms of AalCecA and AalCecC constituted a smaller proportion of these isoforms.
The polycation 1 ,Sdimethyl-1 ,Sdiazaundecamethylene polymethobromide (polybrene) is superior to ... more The polycation 1 ,Sdimethyl-1 ,Sdiazaundecamethylene polymethobromide (polybrene) is superior to calcium phosphate for the introduction of purified DNA into cultured Aedes albopictus (mosquito) cells. Adsorption of the polybrene-DNA complex to mosquito cells was essentially linear for 6 h. However, the rate of adsorption of DNA increased when the DNA-polybrene mixture was preincubated for several hours prior to addition to cells. A recombinant plasmid carrying an inducible chloramphenicol acetyltransferase gene under the control of a Drosophila heat shock protein (hsp) promoter was used to show that expression of transfected DNA was highest when cells were treated with a freshly prepared polybrene-DNA mixture. Optimal expression was observed in cells transfected with 4-13 ug of DNA per lo6 cells; transfection with 24 ug of DNA resulted in reduced CAT expression. Variation in the polybrene-DNA ratio improved transfection with high levels of DNA. In mosquito cells, CAT expression was independent of DNA methyla-tiOn.
The obligate intracellular microbe, Wolbachia pipientis (Rickettsiales; Anaplasmataceae), is a Gr... more The obligate intracellular microbe, Wolbachia pipientis (Rickettsiales; Anaplasmataceae), is a Gram-negative member of the alpha proteobacteria that infects arthropods and filarial worms. Although closely related to the genera Anaplasma and Ehrlichia, which include pathogens of humans, Wolbachia is uniquely associated with invertebrate hosts in the clade Ecdysozoa. Originally described in Culex pipiens mosquitoes, Wolbachia is currently represented by 17 supergroups and is believed to occur in half of all insect species. In mosquitoes, Wolbachia acts as a gene drive agent, with the potential to modify vector populations; in filarial worms, Wolbachia functions as a symbiont, and is a target for drug therapy. A small number of Wolbachia strains from supergroups A, B, and F have been maintained in insect cell lines, which are thought to provide a more permissive environment than the natural host. When transferred back to an insect host, Wolbachia produced in cultured cells are infectio...
In Vitro Cellular & Developmental Biology - Animal, 2018
Wolbachia pipientis (Rickettsiales; Anaplasmataceae) is an obligate intracellular alpha proteobac... more Wolbachia pipientis (Rickettsiales; Anaplasmataceae) is an obligate intracellular alpha proteobacterium that occurs in arthropods and filarial worms. Some strains of Wolbachia can be maintained as persistent infections in insect cell lines. C/wStr1 cells from the mosquito Aedes albopictus maintain a robust infection with Wolbachia strain wStr, originally isolated from the planthopper, Laodelphax striatellus. To explore possible functions of penicillin-binding proteins expressed from the wStr genome, C/wStr1 cells were exposed to ampicillin. Absolute levels of Wolbachia increased 3.5-fold in ampicillin-treated cells and fivefold in naive cells newly infected with wStr. Because cell numbers were depressed by ampicillin treatment, Wolbachia yield on a per-cell basis increased by 15-fold. The absence of a similar effect on wAlbB in Aa23 host cells suggests that the Wolbachia strain, the presence/absence of genes encoding penicillin-binding proteins, or the interaction between wAlbB and its host cells may modulate the effects of ampicillin.
In Vitro Cellular & Developmental Biology - Animal, 2019
Factors that influence establishment of Wolbachia, an obligate intracellular bacterium, in novel ... more Factors that influence establishment of Wolbachia, an obligate intracellular bacterium, in novel insect hosts or uninfected insect cell lines are poorly understood. Infectivity of Wolbachia strain wStr was correlated with flow cytometric profiles to define optimal conditions for harvesting an infectious inoculum. Wolbachia recovered from the cell culture supernatant after gentle pipetting of infected cells represented about 1% of the total bacterial population and were more infectious than Wolbachia that remained associated with intact cells and/or membranes after low-speed centrifugation. Optimal establishment of a robust infection in naïve cells required 6 d, at a ratio of 80 to 160 bacteria per cell. Among Aedes albopictus mosquito cell lines, an aneuploid line with a 4n + 1 karyotype was more susceptible to infection than diploid lines. These findings contribute to the in vitro manipulation of Wolbachia, illustrate some of the many factors that influence infectivity, and identify areas for future investigation.
Treatment with tetracycline or rifampicin to eliminate the obligate intracellular bacterium, Wolb... more Treatment with tetracycline or rifampicin to eliminate the obligate intracellular bacterium, Wolbachia pipientis, provides an important tool for validating Wolbachia’s diverse effects on arthropod reproduction, including cytoplasmic incompatibility, feminization, male killing and parthenogenesis. For the soil collembolan, Folsomia candida (Entomobryomorpha: Isotomidae) efforts to establish the role of Wolbachia in parthenogenesis using tetracycline have been ambiguous, possibly reflecting variation in overall experimental design, mode of antibiotic application and duration of treatment. By maintaining F. candida populations on agar plates containing dissolved antibiotics we show that the EC50 (effective concentration for 50% reduction in biomass) for tetracycline is 50-fold higher than for rifampicin. Experiments with the fluorescent dye rhodamine further show that tetracycline deters feeding. Using individual Collembola, we show that reproductively mature F. candida survive more than 60 days exposure to tetracycline at concentrations 4-fold higher than the EC50 and that its effect on egg production is reversible, consistent with persistence of Wolbachia during tetracycline treatment. As has been shown with other microbes, our results suggest that in F. candida, Wolbachia survives antibiotic exposure by entering a metabolically dormant persister state, from which it can recover under favorable conditions. This possibility is of particular interest because persister cells are induced by toxin-antitoxin (TA) gene pairs, which have recently been associated with Wolbachia-induced cytoplasmic incompatibility in Culex pipiens mosquitoes.
The American Journal of Tropical Medicine and Hygiene, 2001
We have used two-dimensional polyacrylamide gel electrophoresis to examine changes in the relativ... more We have used two-dimensional polyacrylamide gel electrophoresis to examine changes in the relative abundance and diversity of non-secreted proteins in Aedes aegypti fat body preparations during a reproductive cycle. Electrophoretic profiles were evaluated at four time points after eclosion, and at five time points after a blood meal. In contrast to the dramatic changes in abundance of specific secreted proteins such as vitellogenin, our results show that the complement of proteins internal to the fat body remains relatively constant during the mosquito reproductive cycle. Of the approximately 5-10% of proteins that do change in abundance, the majority undergo a dramatic decrease within 24 hours after eclosion.
In Vitro Cellular & Developmental Biology - Animal, 2015
The plant allelochemical L-mimosine (β-[N-(3-hydroxy-4-pyridone)]-α-aminopropionic acid; leucenol... more The plant allelochemical L-mimosine (β-[N-(3-hydroxy-4-pyridone)]-α-aminopropionic acid; leucenol) resembles the nonessential amino acid, tyrosine. Because the obligate intracellular alphaproteobacterium, Wolbachia pipientis, metabolizes amino acids derived from host cells, the effects of mimosine on infected and uninfected mosquito cells were investigated. The EC 50 for mimosine was 6-7 μM with Aedes albopictus C7-10 and C/wStr cell lines, and was not influenced by infection status. Mosquito cells responded to concentrations of mimosine substantially lower than those used to synchronize the mammalian cell cycle; at concentrations of 30-35 μM, mimosine reversibly arrested the mosquito cell cycle at the G1/S boundary and inhibited growth of Wolbachia strain wStr. Although lower concentrations of mimosine slightly increased wStr abundance, concentrations that suppressed the cell cycle reduced Wolbachia levels.
In Vitro Cellular & Developmental Biology - Animal, 2015
Wolbachia pipientis (Rickettsiales), an obligate intracellular alphaproteobacterium in insects, m... more Wolbachia pipientis (Rickettsiales), an obligate intracellular alphaproteobacterium in insects, manipulates host reproduction to maximize invasion of uninfected insect populations. Modification of host population structure has potential applications for control of pest species, particularly if Wolbachia can be maintained, manipulated, and genetically engineered in vitro. Although Wolbachia maintains an obligate mutualism with genome stability in nematodes, arthropods can be co-infected with distinct Wolbachia strains, and horizontal gene transfer between strains is potentially mediated by WO phages encoded within Wolbachia genomes. Proteomic analysis of a robust, persistent infection of a mosquito cell line with wStr from the planthopper, Laodelphax striatellus, revealed expression of a full array of WO phage genes, as well as nine of ten non-phage genes that occur between two distinct clusters of WOMelB genes in the genome of wMel, which infects Drosophila melanogaster. These nonphage genes encode potential host-adaptive proteins and are expressed in wStr at higher levels than phage structural proteins. A subset of seven of the non-phage genes is flanked by highly conserved non-coding sequences, including a putative promoter element, that are not present in a syntenically arranged array of homologs in plasmids from three tickassociated Rickettsia spp. These studies expand our understanding of wStr in a host cell line derived from the mosquito, Aedes albopictus, and provide a basis for investigating conditions that favor the lytic phase of the WO phage life cycle and recovery of infectious phage particles.
A family of nine recombinant bacteriophages containing rRNA genes from cultured cells of the mosq... more A family of nine recombinant bacteriophages containing rRNA genes from cultured cells of the mosquito, Aedes albopietus, has been characterized by restriction mapping, Southern-blotting and Sl-nuclease analyses. The 18S rRNA coding region measured 1800 bp and contained a conserved EcoRI site near the Tend. The 28S rRNA coding region was divided into ,, and fl sequences, comprising 1750 and 2000 bp, respectively, which were separated by a 350 bp sequence that is removed from the rRNA precursor during processing. The entire rDNA repeat unit had a minimum length of 15.6 kb, including a nontranscribed spacer region that contained a series of PvuI repeats upstream of the 18S rRNA coding sequence. During development of the mosquito, Aedes aegypti, the rRNA gene copy number per haploid genome increased from about 400 in larvae to about 1200 in adults.
Comparative Biochemistry and Physiology Part B: Comparative Biochemistry, 1986
In the mosquito Aedes aegypti, quantitative and qualitative changes have been detected in ribonuc... more In the mosquito Aedes aegypti, quantitative and qualitative changes have been detected in ribonuclease activity during development. 2. Ribonuclease activity is particularly high in extracts from larvae, relative to that in extracts from pupae or adults. 3. Larval extract is enriched for a ribonuclease that is heat-labile, has an alkaline pH optimum, and is extremely sensitive to the divalent cation, manganese. 4. Extract from adult females is enriched for a heat-stable component that has an acidic pH optimum and is more active at 56 than at 30°C. 5. Throughout the vitellogenic cycle, no major changes in ribonuclease activity were detected in fat body extracts.
Wolbachia is an obligate intracellular bacterium (Anaplasmataceae, Rickettisales) that occurs in ... more Wolbachia is an obligate intracellular bacterium (Anaplasmataceae, Rickettisales) that occurs in arthropods and filarial worms, and spreads by vertical transmission in the oocyte cytoplasm. In insects, reproductive distortions associated with Wolbachia, such as cytoplasmic incompatibility in mosquitoes, have potential value for controlling pests, including species that transmit human, animal and plant diseases. Wolbachia strains that propagate as a persistent infection in insect cell lines provide an important resource for developing the genetic tools that will facilitate these applications. Here I describe conditions for flow cytometric evaluation of Wolbachia growth in persistently infected mosquito cells. Cytometry parameters were established using uninfected mosquito cells and Escherichia coli as a surrogate for Wolbachia, and quantitation was correlated with cell counts determined with a Coulter electronic cell counter and bacterial counts based on optical density. The protocol was validated by showing depletion of Wolbachia in medium containing tetracycline and rifampicin, and sensitivity of Wolbachia to treatment of host cells with paraquat, an oxidizing agent, and lumiflavin, an inhibitor of riboflavin uptake. The Wolbachia peak on the flow cytometry histogram was shown to contain Wolbachia by DNA analysis using the polymerase chain reaction, and by infection of naive recipient cells. This approach will streamline investigation of Wolbachia growth in insect cell lines and facilitate identification of culture conditions that select for Wolbachia-infected cells.
We examined survival, growth and protein synthesis in mosquito cells that had been maintained for... more We examined survival, growth and protein synthesis in mosquito cells that had been maintained for up to 21 days in serum-free medium. On polyacrylamide gels, protein bands from "starved" cells remained discrete, and despite low levels of incorporation, radiolabeled bands were detectable, suggesting that low levels of protein synthesis were sustained. A prominent band that accumulated in serum-starved cells was digested with trypsin and analyzed by tandem mass spectrometry, which identified the protein as eukaryotic elongation factor (EF)-1α EF-1α is well-conserved among species, and differential accumulation of EF-1α in serumstarved cells was verified by western blotting using a primary antibody to the homologous protein from Trypanosoma brucei. Aside from its importance in the elongation step of protein synthesis, EF-1α has been shown to have a number of non-canonical functions, including interaction with viral RNA and a potential role in apoptosis. We anticipate that the prolonged viability of mosquito cells in serum-free medium may provide a system to explore whether EF-1α accumulation is an adaptive response compatible with resumption of growth in the event that nutrients are replenished, or whether the excess EF-1α represents an irreversible commitment to an apoptotic pathway.
Somatic cell mutants resistant to drugs that interact with the eukaryotic ribosome provide a usef... more 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%.
In Vitro Cellular & Developmental Biology - Animal, 2008
The Aedes albopictus Aa23 cell line, which is persistently infected with Wolbachia pipientis stra... more The Aedes albopictus Aa23 cell line, which is persistently infected with Wolbachia pipientis strain wAlbB, tends to grow as aggregated clusters of cells that are difficult to disperse for conventional quantification based on cell number. We used A. albopictus C7-10 cells to validate conversion of methylthiazole tetrazolium (MTT) to a colored formazan product with respect to incubation time, cell number over a 40-fold range, and metabolic activity as cells enter stationary phase. Using this assay, we showed that the doubling time of Aa23 cells increases from about 45 h early after plating to more than 70 h as the cells reach stationary levels. Growth of Aa23 cells proceeds at similar rates in the presence or absence of tetracycline concentrations that decrease the abundance of Wolbachia. Insofar as the MTT assay reflects mitochondrial function, our results indicate that, in Aa23 cells, abundance of intracellular Wolbachia has no measurable effect on mitochondrial activity in the presence of tetracycline.
In Vitro Cellular & Developmental Biology - Animal, 2008
In vitro production of the obligate intracellular bacterium, Wolbachia pipientis, is essential to... more In vitro production of the obligate intracellular bacterium, Wolbachia pipientis, is essential to its manipulation as a genetic tool to spread transgenes within vector populations. We have adapted the Wolbachia-infected Aa23 Aedes albopictus mosquito cell line to Eagle's minimal medium, supplemented with nonessential amino acids, glutamine, and 20% fetal bovine serum. When plated at low densities, Aa23E cells grew as patchy monolayers, comprised of non-contiguous clusters of cells that gave rise to solid clumps of tightly adherent cells. Multicellular clumps eventually detached from the substrate and floated freely in the medium. Removal of Wolbachia by treatment with tetracycline did not alter the cytological properties of the host cells, which had a population doubling time of 4-5 d. The presence of Wolbachia was monitored by Giemsa staining of cytological preparations, polymerase chain reaction (PCR) amplification of Wolbachia 16S ribosomal DNA, and by simultaneous PCR amplification of ribosomal protein genes from Wolbachia and mosquito host cell genomes. Wolbachia morphology was pleomorphic, and Wolbachia DNA persisted in the culture medium for several weeks after degradation of PCR-amplifiable host cell DNA.
In Vitro Cellular & Developmental Biology - Animal, 2009
We used Wolbachia pipientis strain wAlbB from Aedes albopictus Aa23 cells to infect clonal Ae. al... more We used Wolbachia pipientis strain wAlbB from Aedes albopictus Aa23 cells to infect clonal Ae. albopictus TK-6 cells, which are resistant to 5-bromodeoxyuridine. Infected TK-6 cells were cultured in medium containing 5-bromodeoxyuridine to select against Aa23 cells that might have persisted in the inoculum. Infected TK-6 lines retained the Wolbachia infection for 5 mo, indicating that their metabolic processes support Wolbachia growth and multiplication. To investigate early events after Wolbachia infection, we labeled infected cells with 35 S[methionine/cysteine]. Patterns of labeled proteins on sodium dodecyl sulfate gels were similar in control and infected cells, with the exception of a 29-kDa protein. Tandem mass spectrometry revealed that the 29-kDa band included α and β subunits of the 26S proteasome. Independent confirmation of the up-regulation of the proteasome was established by probing Western blots with a monoclonal antibody to the proteasome-associated co-factor, ubiquitin. Wolbachia's loss of metabolic pathways for the synthesis of most amino acids and retention of pathways for their uptake and metabolism suggest that proteasome activation provides a mechanism whereby controlled degradation of intracellular host proteins would increase availability of amino acids to support establishment and maintenance of the Wolbachia infection.
We have characterized full-length cDNAs encoding three isoforms of the antibiotic cecropin secret... more We have characterized full-length cDNAs encoding three isoforms of the antibiotic cecropin secreted by the C7^10 cell line from the mosquito, Aedes albopictus. The existence of two cecropin isoforms that differed from the previously described AalCecA was predicted by mass spectrometry and amino acid sequence analysis of peptides that eluted from reversed phase high performance liquid chromatography as a single peak just behind the previously described cecropin, AalCecA. Based on the amino acid sequence of the mature AalCecA peptide, we designed primers that amplified partial cDNAs encoding three different A. albopictus cecropins in reverse transcriptase polymerase chain reactions. Rapid amplification of cDNA ends was then used to complete the cDNA sequences of AalCecA, AalCecB and AalCecC, respectively. Each cDNA encoded a translation product containing a signal peptide, a pro region, and a mature cecropin peptide consistent with amino acid sequence data from chymotryptic digests. Although the mosquito cecropins shared 70^86% identity among each other, they shared only V V40% identity to cecropins from Drosophila melanogaster. Each of the cecropins was expressed within 2 to 4 h after induction, and transcripts measuring 0.3 to 0.5 kb continued to accumulate over 24 h. The three cecropins were secreted in roughly equimolar proportions, and 30 to 90% of AalCecB was amidated at the terminal glycine residue. In contrast, amidated forms of AalCecA and AalCecC constituted a smaller proportion of these isoforms.
The polycation 1 ,Sdimethyl-1 ,Sdiazaundecamethylene polymethobromide (polybrene) is superior to ... more The polycation 1 ,Sdimethyl-1 ,Sdiazaundecamethylene polymethobromide (polybrene) is superior to calcium phosphate for the introduction of purified DNA into cultured Aedes albopictus (mosquito) cells. Adsorption of the polybrene-DNA complex to mosquito cells was essentially linear for 6 h. However, the rate of adsorption of DNA increased when the DNA-polybrene mixture was preincubated for several hours prior to addition to cells. A recombinant plasmid carrying an inducible chloramphenicol acetyltransferase gene under the control of a Drosophila heat shock protein (hsp) promoter was used to show that expression of transfected DNA was highest when cells were treated with a freshly prepared polybrene-DNA mixture. Optimal expression was observed in cells transfected with 4-13 ug of DNA per lo6 cells; transfection with 24 ug of DNA resulted in reduced CAT expression. Variation in the polybrene-DNA ratio improved transfection with high levels of DNA. In mosquito cells, CAT expression was independent of DNA methyla-tiOn.
Uploads
Papers by Ann Fallon