Human NTERA cells expressing eGFP under the DCX promoter were maintained in DMEM media containing 10 % FBS. To induce differentiation, cells were plated in 96 well plates. One day after seeding, 10 μM of retinoic acid and designated concentrations of recombinant carrier-free human GDF3 (R&D Systems, Minneapolis, MN; at 0, 10, 50, or 150 ng/mL) were added to the culture media of each corresponding NTERA treatment well. Cells were maintained under these conditions for 2 weeks, during which media was replaced every 3 days. Cells were then cultured for an additional 2 weeks with continued GDF3 treatment, in the absence of retinoic acid.