To test whether MBs have PC potential, we collected MB colonies generated from H1 hESCs differentiated on OP9 and cultured them in the presence of platelet-derived growth factor (PDGF)-BB (Figure 1A), because PDGF-B/PDGFRβ signaling plays the most critical role in PC development in vivo (Levéen et al., 1994; Soriano, 1994). Here, PDGFRB is linked to Mobius syndrome.