The overall goal of this procedure, is to isolate cells into different cell cycle phases using centrifugal elutriation. This method can help answer key questions in the cancer therapeutics field. Because the isolation of cells into separate phases, allows for the interrogation of phase dependent affects of anti-cancer compounds.
The main advantage of this technique is that it allows for separation of cells into specific phases using physical properties, rather than chemical perturbations. To start the experiment, install the strobe assembly into the centrifuge such that the power cord is fed out of the chamber through the port on the left. Adjust the strobe flash lamp so that it lines up with the viewing window, when the centrifuge is closed.
Secure the assembly in place, by tightening two phillips head screws, at the top of each bracket. And then by tightening the thumb screws at the bottom of the bracket. Plug the power cord into the strobe power port, located at the back of the centrifuge.
Next, set the rotors straight down onto the centrifuge drive hub, and firmly secure it with a T handle hex wrench. Then, place the assembly containing the elutriation chamber, counterbalance, rotating seal assembly, and a mounting plate onto the rotor. Push down evenly, placing one hand on the elutriation chamber, and the other hand on the counterbalance, until the bolts on the rotor snap into place.
Place the pin, located at one end of the cable, into the hole in the rotating seal assembly. And secure the eyehole, at the other end, with one of the phillips head screws, affixed onto the bracket to connect the anchoring cable. To assemble the flow system, to pump buffer into and out of the elutriation chamber, connect size 16 tubing to a variable speed pump.
Insert one free end of this tubing through a port at the top left of the centrifuge chamber, such that it enters into the chamber. Attach a fitting to the free end of this tube, and then insert the fitting into the input hole of the rotating seal assembly. Lastly, insert the output tubing, through a port, to attach it to the transfer tube at the top of the rotating seal assembly.
Once the elutriation system is assembled, sterilize it by placing the other free end of the input tubing into a 500 milliliter bottle, filled with 5%bleach. And placing the output tubing into an empty one liter waste bottle. Next, turn on the pump, and allow the bleach to flow all the way through the elutriation system, until it is pumped out into the waste bottle.
Now, turn the centrifuge on and allow it to come to the maximum designated speed to release bubbles and back pressure. Once the set speed is reached, stop the centrifuge. After the rotor has stopped completely, open the lid and inspect the chamber for any leaks.
Next, in a similar fashion, as previously described, run sterile water through the system for 10 minutes. After flushing with water, replace the water reservoir with a sterile glass bottle filled with 100 milliliters of elutriation buffer. Place the input tubing into this bottle, so that it is at the very bottom.
Start the centrifuge, and allow the buffer to flow through the system. After the reservoir bottle is close to empty, and water is fully flushed out of the system, move the output tubing from the waste bottle into the reservoir so that buffer is continuously recycled through the system. Finally, switch on the strobe lamp, and turn the elutriation knob to the extreme left.
Now, adjust the viewing window by slowly turning the knob to the right, so that the elutriation chamber is clearly seen, and the strobe light is in sync with the rotor's speed. Prepare the cell sample as described in the text protocol. Add the resuspended cells into the reservoir bottle containing the recycling elutriation buffer.
Allow the cells to enter into the system and reach equilibrium within the elutriation chamber. To ensure that all cells are retained in the chamber, take a drop of the eluent on a glass slide, and view it under a microscope. If the sample is devoid of intact cells, it confirms the retention in the chamber.
Once all the cells have entered into the chamber, and a distinct boundary at the whitest part of the chamber, containing cells and equilibrium is seen, begin collecting fractions. Move the output tubing to a pre-chilled 50 milliliter conical tube, labeled W1.Collect 50 milliliters of elutriation buffer in this tube and store on ice. Soon after collecting the W1 fraction, lower the centrifuge speed to 821 G.And move the output tube to the conical tube, labeled W2, and collect 50 milliliters more at this speed.
Continue changing the speed, and collecting fractions. Make sure there is medium in the reservoir tank, and always store the collected fractions on ice. After all fractions have been collected, stop the centrifuge, and collect 50 milliliters in a conical tube, labeled stop.
Pellet cells collected in each of the fractions, and using downstream analysis, such as flow cytometry, or western blotting, as required. A line graph displaying the average diameter of cells in successive elutriation fractions, is shown. Note that the larger the cell diameter, the higher the fraction number at which it elutes.
Results from fluorescents activated cells sorting analysis, show the DNA content of cells in each of the 20 elutriation fractions. Early fractions, F1 to F5, contain almost exclusively cells with 2N DNA content representing cells in G1 phase. A mixture of cells in G1 and S phases, was seen in intermediate fractions, F6 to F9.And cells with 4N DNA content, representing cells in G2 to M, were observed starting in F10.
Shown here, are western blot results from probing the levels of cell cycle related proteins in pooled fractions of cells in G1 phase, and G2 to M phase. The G2 to M Pool had higher levels of Phospho-Rb and Cyclin B one, compared to the G1 Pool, as expected. Cyclin D one signal was weak, but nonetheless was detectable in the G1 Pool, and undetectable in the G2 to M Pool.
Once mastered, this technique can be done in three hours if it is performed properly. While attempting this procedure, it is important to remember to take your time, and make sure that the elutriation system is assembled properly, and that all materials and solutions are prepared. Following this procedure, other methods such as cell cycle analysis, cell viability assays and immunoblots can be performed in order to interrogate how therapeutic compounds may be acting in a cell cycle phase dependent manner.
