qPCR showing the transcription levels of the genes Dazl, Oct4, Stra8 and Vasa in iPS cell-derived EBs with or without RA treatment, compared with the control group (EB(7d)) (*P<0.05, **P<0.01). EB, embryoid body; iPS, induced pluripotent stem; qPCR, quantitative PCR; RA, retinoic acid.