1. Trypsinize and aggregate cells into EBs for 48 hours (2*10^6 for six well or 500/20ul in hanging drop).
2. plate EBs/do not plate and change medium to add:
a. BMP4 10ng/ml
b. activin A 3ng/ml
c. VEGF 5ng/ml
Flk1 should beging expression within 3-4 additional days.