Figure 4.

The timing of developmental events during in vitro skin organogenesis using human pluripotent stem cell (hPSCs) derived skin organoid. The human skin organoids are obtained in three main stages. The surface ectoderm and cranial neural crest cells are coinduced in the first stage using hPSCs. As a starting point, these cells form aggregates and then undergo ectodermal induction with critical differentiation factors, including bone morphogenetic protein (BMP) 4, FGF, and a transforming growth factor‐β inhibitor. On day 3, cells erupt outward, leaving the surface ectoderm and undifferentiated hPSC core. When the aggregates are mature (8–12 d), the intermediate layer erupts out, leading to the development of cranial skin. At the end of this stage, skin organoids contain cranial neural crest cells as well as epidermis and dermis precursors. Cystic skin organoids consisting of mesenchymal, neural, and glial progenitor cells surrounded by a sphere of keratinocytes are formed in the second stage. Also, the organoids contain self‐assembled epidermal and dermal layers along with bulb‐like hair follicles. In the third stage, the skin organoids produce a keratinized epidermis with a population of melanocytes, Schwann cells, and sensory neurons. Additionally, hair follicles with sebaceous glands grow outward. Created with Biorender.com.