Preparation of all-trans retinal food

Retinal Food Preparation

Protocol modified from:

• Optogenetics teaching protocol
• Molasses food recipe

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Preparation of All-Trans Retinal (ATR)

• Suspend ATR in ethanol to make a 250 mM stock solution.
• Prepare fly food with a 1:200 dilution → final concentration 0.2 mM.
• ATR does not fully dissolve, resuspend as much as possible.
• Store 1 mL aliquots at -20°C (stable indefinitely).

WarningLight Sensitivity of ATR

All-trans retinal is highly light sensitive. Avoid exposure to strong white light and keep solutions covered with foil whenever possible.

Fly Media Options

Option 1: Pre-made fly media

• Purchase fly media online Archon Scientific
• Supplement with ATR as needed
• Clark lab:
  • Drip ATR onto food surface
• Lacin lab:
  • Scrape food from ~40 vials (~5 mL each)
  • Microwave to melt and cool
  • Add 2 vials of 250 mM ATR to 40 vials

Option 2: Prepare your own fly media

Consumables and Equipment:

• Please refer to the vendors listed by the Bloomington Drosophila Stock Center for supplies and equipment. Vendors Fly supplies.
  • Genesee Scientific is amongst the most cometitvely priced vendors for fly vials, plugs and food.
• A simple kettle on heat plate or turkey roaster oven (~$75.00) are economic solutions for cookign the fly food.
  • Turkey Roaster Oven

Recommended mix:

• Nutri-Fly™ Molasses formulation Genesee Scientific]() (Costs < $3.00 per liter)
  • Nutru-Fly™
• Or use the recipe below:

Yield

• Makes ~1.2 L
• Enough for ~100 vials

Ingredients

Ingredient	Amount
Water	1041.5 mL
Yeast Red Star Active Dry)	26.4 g
Yellow cornmeal	40.8 g
Agar	9.6 g
Molasses	64.83 mL
Tegosept (20% in ethanol)	12 mL
Propionic acid	6.0 mL
Extra water	141 mL

Ingerient vendor: We recommend Genessee Scientific #### Instructions

1. Add ¼ of the water and stir with:
   • agar
   • yeast
   • cornmeal
   • molasses (≥10 minutes)
2. Add remaining water and boil for 20 minutes, stirring to dissolve lumps
3. Add remaining cold water to cool faster
4. When mixture is < 80°C, add:
   • acid
   • tegosept
5. Add 6 mL of 250 mM ATR

WarningProtect from Light During Preparation

After adding ATR, minimize light exposure. Work quickly and keep containers covered with foil when possible.

6. Dispense ~5 mL per vial
7. Dry overnight:
   • cover with cheesecloth
   • seal with Press’n Seal
   • cover tray with foil (light protection)
8. Storage:Best used within 4–6 weeks

TipStorage Tip

Keep prepared vials covered with aluminum foil and store in low-light conditions to preserve ATR activity.