Asymmetric cysts resemble the post-

Asymmetric cysts resemble the post-implantation amniotic sac.We next sought to characterize the cell fates within the asym￾metric cyst using immunofluorescence analysis. The results revealthat the columnar side of the asymmetric cyst is composed of cellsthat prominently retain the pluripotency marker OCT4(also known as POU5F1), which is lost in the squamous cells(Fig. 3a; Supplementary Fig. 5). Co-staining of OCT4 with otherpluripotency markers—NANOG and SOX2—confirms that thecolumnar side of the asymmetric cyst is composed of undiffer￾entiated, epiblast-like cells (Fig. 3b, c), resembling the embryonicdisc at one pole of the human amniotic sac (Fig. 1a). Consistentwith this contention, OCT4/NANOG co-staining as well asSOX2 staining have been seen exclusively in the embryonic discof post-implantation cynomolgus monkey embryos in recentpublications6, 15. Notably, asymmetrically patterned cysts with these characteristics were consistently generated from threehuman embryonic stem cell (hESC) lines (H7, H9, and UM63-1),as well as a human-induced pluripotent stem cell (hiPSC) line1196a (Supplementary Fig. 6).