All-trans Retinal Fly Food
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1. Thaw an aliquot of all-trans retinal stock solution (200 mm) or make a fresh solution.
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2. Prepare fly food as usual until the cooling step before pouring the food into vials.
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If using premade food, heat the food in a microwave until it is liquid.
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3. Let the fly food cool to ∼55°C (the food will be okay to touch for >5 sec).
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4. Vortex the all-trans retinal until all the precipitate is in solution.
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5. Add all-trans retinal to the cooled fly food to obtain a final concentration of 0.5 mm.
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Note that, for regular cylindrical vials, the food volume can be estimated by the following formula:
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We usually add ∼20 µL of 200 mm all-trans retinal to a single vial.
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6. Protect the fly food from light, wrapping single vials in aluminum foil and store them at room temperature (∼22°C–24°C).
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Aluminum foils can be recycled across experiments. We do not recommend using fly food that is older than 2 or 3 weeks as it will get gradually dehydrated, which will modify the hardness of the food.
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