Mesoderm in vitro induction was performed as previously reported (26 (link)). 1.5 × 105 ESCs were seeded per well in ultra-low attachment surface six-well plate (Corning) in modified serum-free differentiation (SFD) medium for 2 days and small EBs were formed. The SFD medium is consisted of IMDM (Gibco, 12440053) and Ham-F12 (Cellgro, 10-080-CVR), supplemented with B27 (Gibco, 12587-010) and N2 supplements (Gibco, 17502-048), Glutamine (Gibco, 25030-081), 10% bovine serum albumin (Invitrogen, P2489), Ascorbic acid (Sigma-Aldrich, A4544), and MTG (Sigma-Aldrich, M6145). To direct mesoderm differentiation, EBs were dissociated into single cells by trypsin and 1.5 × 105 cells were seeded per well in ultra-low attachment surface six-well plate (Corning) in SFD medium containing 5ng/ml Activin A (R&D, 338-AC-010), 5ng/ml VEGF (R&D, 293-VE-010), 0.5 ng/ml BMP4 (Stemgent, 03-0007) for 48 h. To trace the middle stage of cell differentiation, 24 and 48 h samples were collected for analysis.
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