Biochemistry
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Functional Characterization of Carboxylesterases in Insecticide Resistant House Flies, Musca Domestica
Summary August 23rd, 2018
Here, we present a protocol to produce house fly carboxylesterase proteins in vitro with a baculovirus mediated insect cell expression system and later functionally characterize their roles in metabolizing permethrin, thereby, conferring pyrethroid resistance by conducting cell-based MTT assay and in vitro metabolic studies.
Transcript
This method can help the key questions in the field of insect toxicology, such as, if all express the metabolic detoxification genes are involved in insecticide resistance? The main advantage of this technique is that it allows to produce larger scales of proteins, and characterize the function of these proteins in metabolizing of insecticides in vitro. Demonstrating the procedures, will be Xuechun Feng, a grad student in my laboratory.
Xuechen's PhD research is focused on the characterization of function of carboxyl esterase in parasite resistance of house flies, Musca domestica. To begin, mix one microliter of GFP entry plasma DNA, with five microliters of a commercially available C-term linear DNA in 250 microliter PCR tubes. Next, add two microliters of commercially available lambda recombination mix to each of the PCR tubes.
Gently mix the tubes, and incubate them at 25 degrees Celsius overnight. Seed two milliliters of log phase growth insect SF9 cell culture evenly to the wells of a cell culture plate. Then allow the cells to attach for at least three hours at room temperature, in the hood.
Using an inverted phase microscope at 250x, check the cell attachment. Then, remove the cell culture medium, and replace it with two milliliters of Grace's insect medium. After this, prepare transfection mixture A and B solutions according to the text protocol.
Then gently mix transfection mixtures A and B together by tapping the tubes. Incubate the mixture at room temperature, in the hood, for 35 minutes. Next, add the mixture drop-wise, onto the seeded cells.
Seal the wells with tape, and incubate the cells at 27 degrees Celsius, overnight. Replace the two milliliters of Grace's insect medium, with two milliliters of complete growth medium. Then, add 100 micromole Ganciclovir, to each well.
Seal the wells with tape, and incubate the cells at 27 degrees Celsius for 72 hours. 72 hours post-infection, collect the medium from each well, and transfer it to 1.5 milliliter centrifuge tubes. Then centrifuge the tubes at 1500 times G, for five minutes at four degrees Celsius.
Add one milliliter of complete growth medium to the well, and use a microscope with fluorescent light, to observe the infection signs of cells at the P1 baculovirus amplification stage. Transfer the supernatant into new 1.5 milliliter centrifuge tubes, and store them at four degrees Celsius, in dark conditions. After this, seed two milliliters of log phase growth insect SF9 cell culture, evenly, in the wells of a cell culture plate.
Allow the cells to attach for at least three hours at room temperature, in the hood. Inoculate five microliters of P1 virus stock into the cell seeded wells, then, add 100 micromole Ganciclovir to each well. Seal the wells, and incubate the cells for 72 hours at 27 degrees Celsius.
First, culture five milliliters of log phase growth insect SF9 cells, with complete growth medium, in T25 non-treated flasks. Then, add 25 microliters of P1 virus stock solution to infect the cell culture, for 48 hours, with gentle shaking, at 27 degrees Celsius. Using acetonitrile, prepare serial dilutions of 100 millimole permethrin.
Then, seed 200 microliters of infected cell culture supplemented with 300 microliters of complete growth media, into a 24 well plate. Making sure that permethrin is fully dissolved in the acetonitrile, and evenly delivered into each well of the plate. After adding the permethrin, gently shake the plate to fully mix the permethrin in the medium.
After this, seal the plate with tape, and incubate the plate at 27 degrees Celsius, for 48 hours, in dark conditions. Remove the cell culture medium from the plate without disturbing the bottom attached cell layer. Add 200 microliters of the MMT reagent to each well.
Then, incubate the plate at 37 degrees Celsius for four hours, until dark purple formazan precipitants form in each well. Add 500 microliters of DMSO to each well, to fully dissolve the precipitants. Then transfer 200 microliters of the dissolved solution, to each well of a 96 well plate.
Fully dissolving the precipitate into DMSO is crucial for the accuracy of the results. After adding the DMSO into samples in the plate, the samples will be washed using the pipette, for several times, until the precipitate has been fully dissolved. Finally, use a microplate reader to measure the absorbance values of the plate at 540 nanometers.
At the P1 stage, the infection ratio is low. At the P2 stage, the infection ratio was significantly enhanced. At the P3 infection stage, almost all the cells showed symptoms of detachment from the cell culture plate, increases of cell diameter, as well as the cessation of cell growth.
Based on the detected absorbance values, the Md alpha E7 expressing cells showed significantly higher viability, compared to the control CAT cells. While conducting this procedure, it is important to prevent cell contamination in all steps, by wiping the surface of stuffs, such as bottles and tubes, with 70 percentage ethanol before conducting the cell experiments. Following this procedure, some other methods, like the homology modeling and dark analysis, can be performed in order to answer additional questions, like the interactions between carboxyl esterase protein and permethrin ligand.
This technique paved the way for the researchers in the insect toxicology, to explore the functional characterization of the genes and mechanisms in insecticide resistance of insects. Don't forget that working with insecticide can be very harmful, and precautions, such as gloves and lab coats, should always be taken while conducting these procedures.
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