The overall goal of this method is to measure the grooming behavior of Drosophila by quantifying and comparing the remainder of colored brilliant yellow dye on the body of the animals in groomed and ungroomed conditions. This method can help answer key questions in the field of neurobiology and behavioral genetics such as the coordination of fine locomotive skills and the associated molecular regulators and circuits. The main advantage is as of this technique, are that it's rapid, robust and easy to perform by many experimentalists and students at a variety of skill levels.
Demonstrating this procedure will be Frankie Barradale, a student in my laboratory. To begin the experiment, prepare an aspirator to move live Drosophila from a culture vial to the grooming chamber. Using scissors, cut 1.5 feet of Tygon tubing.
Cut at least one inch of the tip of a one milliliter disposable micro-pipette tip and hold the one centimeter square piece of mesh over the 196 inch opening of the cut tip. Snugly place a fresh, one milliliter micro-pipette tip over the mesh and cut tip to create a holding chamber for flies. Cut the extreme tip of the new micro-pipette tip to widen the opening enough to allow the passage of a single fly.
The hole will roughly match the opening of the grooming chamber. Snugly fit the nested tips onto the end of the Tygon tubing. Push the tips into the tube to ensure a tight fit to allow for vacuum pressure.
On the other end of the tubing, cut the tip of a 200 milliliter micro-pipette tip and fit the narrow cut end into the tubing to form the mouth side of the aspirator. To prepare dust aliquot tubes, weigh five milligrams of brilliant yellow dye on weighing paper. Pour the dust into a 8 milliliter micro-centrifuge tube and tightly close the cap.
Next, to prepare ethanol tubes, pipette one milliliter of 100%ethanol into 15 milliliter micro-centrifuge tubes. Label the tubes, cap and save the ethanol tubes for completion of the grooming assay. Also include at least one blank sample with only one milliliter of ethanol without a fly for negative controls.
Assemble each grooming chamber by screwing the sliding top plate with the smaller holes, but leaving the bottom plate with the larger holes removed for the addition of the dust. Place each necessary grooming chamber flat on a table with the top face-down. Load five milligrams of brilliant yellow dye aliquot into each chamber, by tapping the tube against the surface of the chamber above the desired well.
Tap the chamber against the table to ensure that all the dust falls through the mesh to the top of the plate. Then screw the bottom plate onto each chamber, so the wider ends of the conical openings face outward and the holes do not rest over the wells. Secure the bottom plate tightly, so that it does not slide and release dye.
Flip the chamber over and knock it flat against the table a few times so that the dust falls through the mesh to rest on the bottom plate. Slide the top plate of the chamber into the open positions that the small holes align with the 15 wells, allowing the introduction of flies into the individual wells. Load one fly into the mouth aspirator by gently sucking through one end of the aspirator as if using a straw.
Deposit the flies by lightly blowing and directing the opening toward the target. After loading a well, slide the top plate so that the fly is trapped in the chamber and place tape over the opening of the well during the loading of the hole chamber, to prevent the fly's escape while loading the other wells. If multiple flies are aspirated into a single well, leave that opening uncovered until only one fly remains.
After all of the necessary wells are filled with flies, flip the chamber so that the bottom plate is upward and the dust has the potential to coat the flies by falling through the mesh. Tightly secure the top and bottom plates by tightening the screws and vortex the chamber to dust the flies for four seconds. Knock the chamber, top plate face-down against the table twice, so that the dye falls through the other side.
Then, flip the chamber over, top plate face-up and knock the chamber twice, to ensure dye settles on the floor of the bottom chamber, away from the fly, held in the top chamber. For control flies, which are not allowed to groom, immediately proceed to sample preparation. Rest the chamber flat on the table or countertop, with the top plate upward for 30 minutes to allow the flies to groom.
Place the chamber in a noise vibration free space, to keep your environment constant for all grooming experiments. Keeping the chamber level with the top plate upward, gently unscrew the bottom plate and remove it from the chamber, taking care not to lose any dye. Place the chamber on a CO2 pad with low air flow until the flies are anesthetized.
Unscrew the top plate from the chamber, carefully use forceps to grab a leg and remove one dusted fly from each chamber and deposit it in a 1.5 milliliter micro-centrifuge tube containing ethanol. Once each micro-centrifuge tube contains one fly, close the cap and invert the tubes three times to agitate and mix the solution of dye and ethanol. Incubate the tubes containing ethanol and flies for five hours at room temperature to ensure full removal of the dye from the fly into solution.
After five hours, briefly vortex each tube for two seconds to ensure clearance of the dyes from the flies. Aliquot 50 microliters of the experimental 1.5 milliliter tube into a well of a 96 well plate, taking note of the location of each sample on the plate. Add 200 microliters of ethanol to dilute the sample five times to avoid sealing effects of heavily dusted flies or large grooming defects.
Use a plate reader to analyze each sample at 397 nanometers. Record the sample through the plate reader and save the spreadsheet with the recording samples on the plate. We used this method to study DopR by comparing the grooming performance of a strong hypomorph and to null DopR mutants to a wild type strain.
The DopR mutants retained significantly more dye than their wild type of rescued counterparts, indicating that the DopR mutants were less efficient at grooming behavior. In a parallel experiment of Rutabaga flies, mutants display the higher dye accumulation levels than DopR mutants, suggesting a significant role of DopR in grooming behavior. After watching this video, you should have a good understanding of how to handle flies for behavioral assays and also measure the grooming behavior.
