Altman:Protocols/Protein Purification/SF9 transfection

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Department of Physics, Willamette University


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Direct transfection of SF9 cells for small-scale protein purification

(Protocol is from DA, based on ZB, based on Novagen protocol)

  • This protocol is for transfecting 15 mL cultures of SF9 cells at 1*10^6 cells/mL. 3 mL of DNA:lipid complexes are used for each 15 mL culture of cells. The protocol can be scaled up slightly by making a larger batch of DNA:lipid complexes (I have made up to 10 mL at a time) and splitting it among multiple 15 mL cultures in separate flasks.

1. Determine the cell density PROTOCOL FOR COUNTING CELLS: 1) Get SF9 cells from the incubator shaker, and put in TC hood 2) Remove 100 μL of the cells, being sure to shake the flask beforehand 3) Dilute the cells 5x with Trypan+PBS (Trypan+PBS = 1:1 Trypan blue + PBS) 4) Place 10 μL in a hemocytometer (from Shirley’s bench) 5) Count the cells in 4 square grids 1 grid = 10-4 mL grid Number of cells Number of dead cells 1 2 3 4 Mean # of total / dead cells per grid = Viability of cells = Cell Density = (mean # of cells per grid)*5*10^4 cells/mL = 2. Determine the volume of cells required for the day Each transfection requires 15 mL of SF9 cells at 1*10^6 cells/mL, or 1.5*10^7 cells 3. Wash the cells by spinning 10 min at 2000 rpm in a swinging bucket centrifuge. Remove the supernatant, and re-suspend the pellet in unsupplemented SF 900 II media to a cell density of ~1.5*10^6 cells/mL (10 mL of media per transfection). 4. Replace cells in 28° shaker until the complexes are ready for transfection 5. Dilute ~10 μg of plasmid DNA in 1.5 mL unsupplemented media; mix by inverting tube 6. Dilute 150 μl of ESCORT IV cationic lipids in 1.35 mL of unsupplemented media; mix by inverting tube 7. Add diluted DNA dropwise to diluted lipids, mixing while adding. Ensure complete mixing by inverting tube afterwards. Allow mixture to sit in the hood for at least 15’ to promote complex formation. 8. Meanwhile, retrieve and count unsupplemented cells; dilute the cells to a final density of 1.25 *10^6 cells/mL in unsupplemented media.

Mean # of total / dead cells per grid = Viability of cells = Cell Density = (mean # of cells per grid)*5*10^4 cells/mL = 9. Dispense 12 mL of cell culture into a plastic 125 mL culture flask (disposable flask with a vented top; 0.2 μm pore) 10. Add 3 mL DNA:lipid complexes to the cell culture.

11. Replace cell culture in 28° shaker; cells may be harvested in 48-72 hours.
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