Abstract
Hair follicle (HF) development and pigmentation are complex processes governed by various signaling pathways, such as TGF-β and FGF signaling pathways. Nestin + (neural crest like) stem cells are also expressed in HF stem cells, particularly in the bulge and dermal papilla region. However, the specific role and differentiation potential of these Nestin-positive cells within the HF remain unclear, especially regarding their contribution to melanocyte formation and hair pigmentation. Bone morphogenetic protein 4 (BMP4), members of the TGFβ family, has been implicated in regulating HF growth, coloration, and related cellular behaviors. Its role in directing Nestin-positive cells toward a melanocytic lineage has yet to be fully explored. In this study, mouse HF organoids were constructed and shown to be an ideal model for studying HF growth and development in vitro. Using this model as a basis, we demonstrated that BMP4 controls HF coloration as well as its length, number, and even size. Furthermore, Nestin-positive cells in the HF-especially those in the bulge region-differentiate into melanocytes, which produce the pigments that give HF its color under BMP4 stimulation. The resulting increase in pigmentation within the mouse HF organoids underscores that BMP4 has a major regulatory role in the formation of melanocytes from Nestin-positive stem cells. This research provides insights into the cellular mechanisms underlying hair pigmentation and suggests potential therapeutic applications for pigmentation disorders.