Characterization of a leucokinin binding protein in Aedes aegypti (Diptera: Culicidae) Malpighian tubule

The insect myokinin (leucokinin-like) neuropeptide family includes peptides that have different physiological effects such as the induction of hindgut myotropic activity and stimulation of urine production. The C-terminal pentamer of myokinins Phe-X-(Ser/Pro/Ala)-Trp-Gly-amide [X=Phe, His, Asn, Ser or Tyr], had been previously determined as the minimum fragment able to elicit a functional response. The receptor(s) for these insect neuropeptides has not yet been identified. In order to characterize the Malpighian tubule leucokinin-like peptide receptor(s) from the yellow fever mosquito (Aedes aegypti), a leucokinin photoaffinity analogue (LPA) of sequence dAla-dTyr-Bpa-dLys-Phe-Phe-Ser-Trp-Gly-amide was designed based on structure/activity relationships for leucokinins. LPA caused depolarization of the transepithelial voltage (TEV) in female Malpighian tubule, confirming the activity of the peptide. The effective concentration to give half the maximum depolarization (EC(50)) was 17 nM. The (125)I-LPA was then used to characterize leucokinin binding proteins in female Malpighian tubule membranes. It specifically labeled and saturated a protein(s) of about 54 kDa as shown by SDS-PAGE/autoradiography and by competition experiments with excess unlabeled leucokinin analogues. (125)I-LPA bound to the 54 kDa protein(s) with a K(d) value of 13+/-3 nM in agreement with the EC(50) for the TEV bioassay. Altogether these data suggest that the 54 kDa protein is an Aedes-leucokinin receptor. This is the first characterization of an insect leucokinin receptor and reveals that LPA is a powerful tool to label insect myokinin receptors.

Cloning of the 16-kDa V-ATPase proteolipid subunit from the red imported fire ant Solenopsis invicta buren (Hymenoptera: Formicidae)

V-ATPases are ubiquitous proton pumps found in eukaryotes, and are important in regulating the pH of cell compartments and in creating membrane potentials. The V-ATPase creates a proton gradient that is used as an energy source for the transport of other ions. The 16-kDa proteolipid is the proton-translocating subunit c of V-ATPases. Using PCR methods, we have cloned the fire ant 16-kDa subunit c, providing the first molecular characterization of this protein in a social insect. Northern blot analysis revealed three possible different transcripts. The presence of V-ATPases in ant Malpighian tubules had been previously demonstrated, where they provide the proton gradient necessary for the excretion of other ions and the formation of primary urine. The 16-kDa proteolipid is highly conserved among insects, and in ants may be important to the critical processes of diuresis and olfaction as a key component of the V-ATPase. Arch.

Cloning and transcriptional expression of a leucokinin-like peptide receptor from the southern cattle tick, Boophilus microplus (Acari: Ixodidae)

Leucokinins are invertebrate neuropeptides that exhibit myotropic and diuretic activity. Only one leucokinin-like peptide receptor is known, the lymnokinin receptor from the mollusc Lymnaea stagnalis. A cDNA encoding a leucokinin-like peptide receptor was cloned from the Southern cattle tick, Boophilus microplus, a pest of cattle world-wide. This is the first neuropeptide receptor known from the Acari and the second known in the subfamily of leucokinin-like peptide G-protein-coupled receptors. The deduced amino acid sequence exhibits 40% identity to the lymnokinin receptor. The receptor transcript is present in all tick life stages as determined by semiquantitative reverse transcription polymerase chain reaction. We also propose that the sequence AAF50775.1 from the Drosophila melanogaster genome (CG10626) encodes the first identified insect leucokinin receptor.

Cloning of an aquaporin-like cDNA and in situ hybridization in adults of the mosquito Aedes aegypti (Diptera: Culicidae)

A cDNA encoding a putative water channel protein, aquaporin, was cloned from a cDNA library of Aedes aegypti Malpighian tubules. The cDNA encodes a 26.11 kDa protein similar to insect aquaporins from Haematobia irritans exigua (Diptera) and Cicadella viridis (Homoptera), and to mammalian aquaporin 4. Localization of the messenger RNA (mRNA) was performed by in situ hybridization of Malpighian tubules and analysed by fluorescence and confocal microscopy. The mRNA was localized in tracheolar cells associated with the Malpighian tubules. No signal was detected in the Malpighian tubule epithelium. The molecular mechanisms for water movement between tissues and tracheoles are not yet elucidated in insects. Our results suggest a model to explain fluid movements in tracheoles during insect respiration.

Insecticide resistance status, esterase activity, and electromorphs from mosquito populations of Culex quinquefasciatus Say (Diptera: Culicidae), in Houston (Harris County), Texas

Culex quinquefasciatus Say is a vector of St. Louis encephalitis (SLE) in Texas. This disease is endemic and prevalent in the Houston area. Disease prevention through mosquito control is mainly targeted against adults by application of a resmethrin-piperonyl butoxide formulation (Scourge). Immature mosquitoes were collected from eight areas in Harris County during 1998. The susceptibility status of these populations to Scourge, malathion, and resmethrin, the latter alone or with an esterase inhibitor as a synergist, was determined using a bottle assay with females. The population structure was investigated by electrophoretic analysis of esterases and their activity. Individual females were also analyzed for esterase activity by plate assay and for isoenzyme pattern by native PAGE. Bioassays indicated high levels of resistance to malathion in all areas. In addition, the effectiveness of Scourge in mosquitoes from area 51 deteriorated throughout the season. A localized, distinctive esterase pattern and activity level was observed in mosquitoes from different areas. Overall, the frequency of esterases Est alpha 2 (A2)/Est beta 2 (B2) was higher than that of Est beta 1 (B1). Altogether, these results indicate the onset of a fragile situation for mosquito control that should be further analyzed to effectively maintain the SLE prevention program for Harris County.

Isolation of the V-ATPase A and c subunit cDNAs from mosquito midgut and Malpighian tubules

Using conserved amino acid sequences for the design of oligonucleotide primers, we isolated cDNA clones for two subunits of the V-ATPase from the midgut and Malpighian tubules of Aedes aegypti larvae. The 3.1 kb cDNA of the A subunit of the peripheral catalytic V1 sector codes for a protein of 68.6 kDa. The protein contains conserved motifs, including an ATP/GTP binding site, found in all other A subunits. Southern analysis using the A subunit as a probe suggests the presence of only a single copy of gene in the Aedes aegypti. The 0.85 kb cDNA of the c subunit of the membrane H+ conducting V0 sector codes for a protein of kDa. This protein has four transmembrane domains and contains a conserved glutamic acid that serves as the binding site for dicyclohexylcarbodiimide. Southern analysis using the c subunit as a probe suggests the presence of more than one related gene in the genome of Aedes aegypti. Pileup analysis of various A and c subunits shows that these subunits fall into distinct clusters, including one in which all arthropod proteins are clustered.

Ductin, a component of the V-ATPase, is developmentally regulated in Heliothis virescens midgut, and anti-ductin antibodies label lateral membranes

We previously cloned from Heliothis virescens a 16-kDa protein that is homologous to other ductin sequences. We also reported its immunolocalization with a specific affinity-purified anti-peptide antibody in the midgut and Malpighian tubule of feeding larvae, and concluded that the cloned proteolipid encodes the V-ATPase proton-transporting subunit c from the V0 sector. We now present the immunolocalization of this protein in the midgut during the L4-L5 larval molt and early post-ecdysis into the fifth instar in H. virescens. The results show that the spatial expression of the 16-kDa protein is developmentally regulated. Labeling by anti-peptide antibody varies during the molt in the midgut goblet cell apical plasma membrane and the goblet cell apical valve. Epifluorescence and confocal microscopy revealed strong anti-ductin labeling in areas of cell-to-cell contact during the molt, and during early post-ecdysis into the fifth larval instar. The characteristic labeling pattern observed in areas of cell-to-cell contact is consistent with the claimed involvement of ductins in gap junctions. Conclusive evidence for the presence of the 16-kDa protein in areas of cell-to-cell contact in the midgut of feeding larvae is, however, lacking. V-ATPase regulation during the molt was also investigated by simultaneous immunohistochemistry with an anti-B subunit antiserum, a probe for the V1 sector.

Immunolocalization of the 17 kDa vacuolar H(+)-ATPase subunit c in Heliothis virescens midgut and malpighian tubules with an anti-peptide antibody

The transmembrane sector of V-ATPases is involved in proton conduction across the membrane where a 15-17 kDa proteolipid forms a putative proton channel. An affinity-purified rabbit polyclonal antibody was developed to an antigenic and putatively extracellular region of a cloned 17 kDa proteolipid. In larval tissue sections, this antibody labeled the midgut goblet cell apical membrane in Heliothis virescens (Lepidoptera: Noctuidae) and the apical membrane in Malpighian tubules from H. virescens and Manduca sexta (Lepidoptera: Sphingidae). The antibody also recognized the 17 kDa protein in an immunoblot of H. virescens Malpighian tubule homogenate. Northern blot analysis revealed the presence of two transcript sizes in the midgut (1.9 and 1.2 kb) and Malpighian tubules (2.2 and 1.9 kb). Our results strongly support the hypothesis that the 17 kDa protein is a component of the V-ATPase, where it is thought to be the proton-conducting subunit. This polyclonal antibody may provide a powerful tool for V-ATPase regulation studies, while the use of the anti-peptide antibody approach may be helpful for the immunolocalization of other ductins.

Sequence of a 17 kDa vacuolar H(+)-ATPase proteolipid subunit from insect midgut and Malpighian tubules

A 0.4 kb polymerase chain reaction (PCR) product obtained from cDNA made from the midgut and Malpighian tubules of fifth instar larvae of Heliothis virescens was used to screen a larval midgut and Malpighian tubules cDNA library. Four clones were obtained, one of 1.9 kb and others of 1.4 kb. The 1.9 kb clone encodes a 17.2 kDa protein which is highly homologous to other vacuolar ATPases proteolipids. Putative N-glycosylation and DCCD binding sites were observed at amino acid residues 83 and 139, respectively.

The parasporal inclusion of Bacillus thuringiensis subsp. shandongiensis: characterization and screening for insecticidal activity

The parasporal body of Bacillus thuringiensis subsp. shandongiensis was characterized in terms of its structure, protein composition, and toxicological properties against several types of insects. The crystals of B. thuringiensis shandongiensis appear to consist of a major protein of 144 kDa present in an spherical inclusion, as determined by transmission electron microscopy, titration curve analysis, and SDS-PAGE of the solubilized crystals. A second protein of ca. 60 kDa is present in trace amounts and appears to be associated with a small bar-shaped inclusion. The 144-kDa protein has been characterized by isoelectric point determination, N-terminal amino acid sequence analysis, amino acid analysis, and immunological cross reactivity. Its N-terminal amino acid sequence differed from that of other B. thuringiensis crystal proteins. The 144-kDa protein was not immunologically related to the crystal proteins of two toxic serovars (B. thuringiensis israelensis and B. thuringiensis kurstaki HD-1) and one nontoxic serovar (B. thuringiensis indiana), as shown in immunoblots probed with antiserum raised against the 144-kDa B. thuringiensis shandongiensis protein, the B. thuringiensis israelensis crystal proteins, and the trypsin resistant fragment of B. thuringiensis kurstaki P1 proteins. In contrast to most B. thuringiensis serovars, B. thuringiensis shandongiensis crystals did not dissolve at pH 12. Solubilization was achieved in sodium bicarbonate at pH 8.3 and in the presence of 25 mM dithiothreitol.(ABSTRACT TRUNCATED AT 250 WORDS)