Melanoblasts' proper location and timed differentiation depend on Notch/RBP-J signaling in postnatal hair follicles.

The Notch/RBP-J pathway is involved in a variety of developmental processes and in tissue homeostasis. In the melanocyte lineage, it has been shown that Notch signaling acts through Hes1 to maintain the melanocyte stem cell population in the hair follicle. This study was designed to determine whether Notch signaling is implicated in other steps of melanocyte-lineage postnatal development. For this purpose, we developed mice in which the RBP-J gene was conditionally ablated in the melanocyte lineage and used the Dct-lacZ reporter transgene to track melanocytes and their precursors in individual hair follicles. We determine that Notch/RBP-J-deficient melanoblasts are in reduced number within the hair follicle and gather within its lower permanent part. Moreover, our results show that Notch signaling is necessary to prevent differentiation of melanocyte stem cells and of melanoblasts before they reach the hair bulb. Finally, our data show that Notch signaling is involved in proper location of melanoblasts in the outer root sheath and of melanocytes in the hair matrix. These findings reveal previously unrecognized roles for Notch signaling in the melanocyte lineage.