The overall goal of this procedure is to analyze the expression and production of genes and protein markers, respectively, of neural differentiation of mouse embryonic stem cells. This method can help determine the mechanism responsible for the inhibition of neural differentiation by the raw age of DPAs, and lead to better protocols to differentiate stem cells into neurons for therapeutic purposes. The main advantage of this technique is that it facilitates tracking the process of neural differentiation at the emerin and protein levels, including by optical microscopy.
Demonstrating the procedure will be Dr.Junning Yang, a research associate in my laboratory. Begin embryoid body formation by harvesting embryonic stem cells with 0.25%Trypsin-EDTA for two to five minutes at 37 degrees celsius, 5%carbon dioxide. Add fresh Iscove's Modified Dulbecco's Medium, or IMDM, with 15%FBS to the detaching cells, and transfer the cell suspension to a 15 milliliter tube.
Centrifuge at 160 x G for five minutes at room temperature. Then count the cells using a hemocytometer, and prepare a five x 10 to the fifth cells per milliliter suspension in IMDM with 0.5 micromolar retinoic acid. Next, use an eight-channel pipette and 200-microliter tips to plate 120-microliter drops per 100 millimeter petri dish.
Invert the dish and fill the inverted lid with PBS to prevent hanging drops from drying. Culture at 37 degrees celsius, 5%carbon dioxide, for three to four days. Use 200-microliter pipette tips to harvest hanging drop embryoid bodies grown for three days.
Touch an embryoid body with a pipette tip, and transfer it to a fibernectin-coated cover slip in a 24-well plate. Change the medium on the cultures every two to three days. When changing the medium, collect the used medium for protein secretion analysis as needed.
To detect secreted proteins in the medium, transfer 500 microliters of embryoid body medium to 10 kilodalton cutoff centrifugal filters, and spin at 20, 000 x G at four degrees celsius. Examine the medium remaining inside the centrifugal filters every 15 to 20 minutes to prevent excessive enrichment. Stop centrifugation when the volume of the remaining medium has fallen to 25 microliters.
Invert the filter and spin at 160 x G at four degrees celsius, then collect the remaining concentrated medium by following the manufacturer's instructions. For a 3D culture, harvest embryoid bodies grown for four days as hanging drops with 200-microliter pipette tips, as before. Transfer 30 embryoid bodies to a 1.5 milliliter centrifuge tube, then prepare collagen gel solution by diluting appropriate volumes of collagen solution and 5X DMEM, adding the neutralization solution, and immediately mixing well.
Place the collagen gel on ice. Next, pipette an appropriate volume of chilled collagen solution into the tube containing the embryoid bodies, and then gently pipette the embryoid body suspension into the wells of a six-well plate without creating bubbles. Immediately transfer the plate to 37 degrees celsius, 5%carbon dioxide, for 60 minutes to initiate collagen polymerization.
After the 60 minutes, overlay the plate containing the embryoid bodies with IMDM. For embryoid body dissociation, again collect the four-day hanging drop embryoid bodies with 200-microliter pipette tips. This time, transfer them to a non-adhesive bacteriological petri dish containing IMDM with 15%FBS and culture at 37 degrees celsius, 5%carbon dioxide, for four more days.
Check the embryoid bodies twice every day to make sure they do not attach to the bottom. Gently shake the dish to prevent embryoid body attachment. After four days, transfer the embryoid bodies to a centrifuge tube and centrifuge at 185 x G for five minutes at room temperature.
Following centrifugation, remove the supernatant. The palette volume should not exceed 100 microliters. Next, pipette one milliliter of 0.25%type I collagenase, supplemented with 20%FBS in PBS into the tube of embryoid bodies.
Incubate the mixture for one hour at 37 degrees celsius and 5%carbon dioxide. Gently pipette the suspension using a one-milliliter pipette tip every 20 minutes. After the incubation, gently wash the cells three times with PBS.
If cell aggregates are present, use a cell strainer with a 100-micron mesh to remove them. Plate the cells on gelatin-coated cover slips in IMDM, then incubate at 37 degrees celsius and 5%carbon dioxide. Wash the 2D or dissociated 3D embryoid bodies with PBS.
Then fix with four percent paraformaldehyde and PBS for 30 minutes at room temperature. After washing the fixed cells three times with PBS to remove floating cell debris, add 1%triton X-100 in PBS to permeabilize the cells for 20 minutes at room temperature. After washing as before, remove the last wash and block with 5%BSA in PBS for 30 minutes.
Towards the end of the incubation, prepare a primary antibody dillution in 1%BSA in PBS supplemented with 0.03%triton X-100. When the 30 minutes has elapsed, replace the blocking solution with the primary antibody solution. Incubate for three hours at room temperature, or overnight, at four degrees celsius.
After washing, apply a secondary antibody in PBS and incubate for one hour at room temperature. Finally, mount cover slips on glass slides with an anti-fade medium for optical microscopy. This image shows sprout emergence from an embryoid body generated from ESCs, positive for two copies of the Syx gene, which codes for a guanine exchange factor that activates the GTPase RhoA.
The image was taken after six days in 3D culture. This embryoid body formed from Syx KnockOut ESCs demonstrates increased sprouting after the same time in culture. Here, phase images of 2D embryoid body edges show that cells expanded faster from Syx KnockOuts than from Syx wild-type.
These immunofluorescence images illustrate that the neural differentiation marker, Nestin, shown in red, was more abundant in cells expanding from six-day 2D6 KnockOut embryoid bodies than from their Syx wild-type counterparts. Here, immunofluorescence images show that the neural differentiation markers Nestin and beta III Tubulin were more abundant in cells dissociated from 13-day 3D6 KnockOut embryoid bodies than from their Syx wild-type counterparts. This is a time-consuming procedure because of the duration of embryoid body growth and differentiation.
It not only requires at least eight days, but in some cases we follow differentiation up to 24 days. While attempting this procedure, it is important to remember to limit the viability of embryoid body diameter to ensure similar differentiation rates along the embryoid bodies.
