Materials and Reagents

Mouse ESCs (mESCs)
0.1% gelatin (Sigma-Aldrich, catalog number: G1393 )
Murine embryonic fibroblast (MEF) feeder cells
Alkaline Phosphatase Staining Kit (Stemgent, catalog number: 00-0009 )
1. Fixation Solution
2. AP Staining Solution A
3. AP Staining Solution B
1x PBS (see Recipes)
1x PBS-T (see Recipes)
1x PBS-glycerol (see Recipes)

Equipment

6-well plate or 24-well plate
Aluminum foil
Light microscope with 10x objective

Procedure

Cell Culture
1. Coat plates with 0.1% gelatin. Warm gelatin to 37 °C. For each well of a 6 well plate, asceptically add 1.5 ml of 0.1% gelatin. Incubate the plates in the tissue culture hood at room temperature for 30 min. Aspirate off the gelatin and allow to dry for 10 min prior to adding media and plating cells.
2. Seed each well with 4.75 x 10⁵ murine embryonic feeder cells (MEFs) in 2 ml of media. Allow the MEFs to attach overnight prior to plating out the mouse ESCs.
3. Passage actively dividing cells and culture for 3-5 days to a subconfluent density prior to staining. For mouse ESCs (mESCs) approximately 1 x 10⁵ cells are plated to each well of a 6-well plate (or 1 x 10⁴ cells for 24-well plate) that has been previously coated with 0.1% gelatin and plated with murine embryonic fibroblast (MEF) feeder cells.
Alkaline Phosphatase Staining
1. Aspirate the culture media from each well and rinse with 1x PBS-T.
2. Aspirate the rinse solution and fix the cells with Fixation Solution at room temperature for two minutes. Use a sufficient volume to endure complete coverage of the cells. This would be 500 µl for each well of 24-well plate or 2 ml for each well of a 6-well plate. It is important not to exceed the fixation time of two min. Over fixation will result in the loss of AP activity and inaccurate results.
3. Aspirate the Fixation Solution and rinse with 1x PBS-T. The wells should not be allowed to dry out.
4. Prepare the Staining Solution by Mixing Solution A and Solution B at a 1:1 ratio. To ensure that there is sufficient volume for staining, prepare (n+1) y volumes of the solution where n is the number of wells, and y is the volume per well. For a 24-well plate y = 500 µl. For a 6-well plate y = 2 ml. The staining solution should be freshly prepared and used within five minutes of preparation.
5. Aspirate the 1x PBS-T and pipet on the prepared Staining Solution. Cover the plate with aluminum foil in the dark for approximately 15 min. Monitor the color change (pluripotent cells will stain red/purple, MEFs will remain colorless) to avoid non-specific staining.
6. Remove the staining solution by aspiration and wash the cells two times with 1x PBS. Do not use 1x PBS-T as this may wash out the stain.
7. Aspirate the 1x PBS. Add 1x PBS-glycerol for long-term storage at 4 °C.
Enumeration of Pluripotent Cells
1. Count the number of AP stained (red/purple) pluripotent colonies and the differentiated (clear) colonies by eye or using a light microscope with 10x objective. The MEF feeder cells will remain clear.

Recipes

1x PBS (for 1 L)
800 ml MilliQ H₂O
8 g NaCl
0.2 g KCl
1.44 g Na₂PO₄
0.24 g KH₂PO₄
Adjust the pH to 7.4 with HCl
Add MilliQ H₂O to a final volume of 1 L
Filter sterilize and stored at 4 °C until use
1x PBS-T (1 L)
800 ml MilliQ H₂O
8 g NaCl
0.2 g KCl
1.44 g Na₂PO₄
0.24 g KH₂PO₄
500 µl Tween-20
Adjust the pH to 7.4 with HCl
Add MilliQ H₂O to a final volume of 1 L
Filter sterilize and stored at 4 °C until use
1x PBS-Glycerol (1 L)
500 ml MilliQ H₂O
8 g NaCl
0.2 g KCl
1.44 g Na₂PO₄
0.24 g KH₂PO₄
200 ml Glycerol
Adjust the pH to 7.4 with HCl
Add MilliQ H₂O to a final volume of 1 L
Filter sterilize and stored at 4 °C until use

Acknowledgments

This work was supported by grants from Genome Canada, the Ontario Genomics Institute, the Stem Cell Network, and the Canadian Institutes of Health Research.

References

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