Tissue localization of overproduced esterases in the mosquito Culex pipiens (Diptera : Culicidae)

We have investigated the tissue distribution of overproduced esterases A (A 1 and A2) and B (B1 and B2) in strains of Culex pipiens L. by immunocytoche mistry. S-LAB mosquitoes, lacking overproduced esterases, were used as refe rence. Tissues showing a strong specific reaction (fluorescence) were obser ved with anti-esterase A1 antiserum in S54 (with Al) and BOUAKE (with A2) s trains, and with anti-esterase BI antiserum in TEM-R and EDIT (with B1) and BOUAKE (with B2) strains. Overproduction of esterases A and B was tissue-s pecific. The most constant pattern for the two types of esterases was their overproduction in the alimentary canal and Malpighian tubes, although fluo rescence varied in intensity depending on strains and developmental stages. There was no difference in the tissue distribution of esterases A1 and A2. In contrast, esterases B pattern was highly variable among strains. Differ ences between TEM-R and EDIT were explained by the different overall overpr oduction and number of copies of the amplified gene (10-fold higher in TEM- R). The most striking difference in esterase BI and B2 tissue localization concerned the nervous system where neurons were intensely fluorescent in TE M-R and EDIT (B1), but not in BOUAKE (B2). All esterase B positive tissues in TEM-R contained large quantities of esterase BI mRNA (in situ hybridizat ion), indicating that at least part of the protein revealed by immunochemis try was produced in the tissues where it was observed. Our results are disc ussed in terms of the protection that the different esterases can confer du ring exposition to organophosphorous insecticides.