목적: The inner ear originates from an embryonic ectodermal placode and rapidly develops into a three-dimensional structure (the otocyst) through complex molecular and cellular interactions. Organoids are being produced in various organs including the inner ear. Many genes and their products are involved in inner ear induction, organogenesis, and cell differentiation. By modulating Matrigel, bone morphogenetic proteins (BMPs), transforming growth factor-beta (TGF-β), fibroblast growth factors (FGFs), and Wnt agonists, otic (inner ear) organoids could be produced from human induced pluripotent stem cell (iPSCs). However, otic organoids had limitations in the absolute number of hair cells and their maturity. The retinoic acid (RA) is a form of vitamin A and is essential for the development of various tissues and organs during embryogenesis, including the inner ear. RA signaling has been shown to play a crucial role in the development and maintenance of the inner ear. It is involved in patterning and differentiation processes that lead to the formation of sensory structures, including hair cells, in the inner ear. This study suggested that RA can promote the differentiation of hair cells from human induced pluripotent stem cells (iPSCs), thereby increasing the number of hair cells in otic organoids. 방법:The differentiation protocols we used in this study were based on the established ones suggested by Hashino et al. CMC-hiPSC-011 (KNIH) and mND2-0 (WiCell) cells as human iPSCs were used. It has been known to take about 90 days in human iPSCs to the formation of otic organoids. We added retinoic acid; it was known to involve in patterning and differentiation processes of sensory structures, including hair cells, in the inner ear. In otic organoids generated from human iPSCs, it was treated at D13-18. The efficiency of the otic organoids was assessed by immunohistochemistry (IHC) and qRT-PCR. 결과:According to the protocol, hair cell-like cells were successfully differentiated from human iPSCs, showing hair cell markers and attached nerve endings. In otic organoids differentiated from human iPSCs, the group treated with RA on days 13 to 18 was more effective in the proliferation of hair cells. In IHC, morphologically, RA treatment showed more effective in the expression of otic markers ECAD and PAX8, hair cell marker (Myo7a), and supporting cell marker (SOX2). And in qRT- PCR, the expression of hair cell markers Myo7a, Atoh1, Espin, and Pou4F3 was also increased in otic organoids with RA treatment. 결론:Otic organoids from human iPSCs, could be successfully produced. Further treatment of RA showed the possibility of otic organoid production with higher efficiency, which will enable the production of stable otic organoids that can be used for the purpose of organoid techniques.