The Notch signalling pathway in hair growth

The Notch signalling pathway is an important mediator of cell fate selectio n whose involvement in epidermal appendage formation is now becoming recogn ised. Hair follicle development and hair formation involve the co-ordinated differentiation of several different cell types in which Notch appears to have a role. We report intricate expression patterns for the Notch-1 recept or and three ligands, Delta-1, Jagged-1 and Jagged-2 in the hair follicle. Notch-1 is expressed in ectodermal-derived cells of the follicle, in the in ner cells of the embryonic placode and the follicle bulb, and in the suprab asal cells of the mature outer root sheath. Delta-1 is only expressed durin g embryonic follicle development and is exclusive to the mesenchymal cells of the prc-papilla located beneath the follicle placode. Expression of Jagg ed-1 or Jagged-2 overlaps Notch-1 expression at all stages. In mature folli cles, Jagged-1 and Jagged-2 are expressed in complementary patterns in the follicle bulb and outer root sheath, Jagged-1 in suprabasal cells and Jagge d-2 predominantly in basal cells. In the follicle bulb, Jagged-2 is localis ed to the inner (basal) bulb cells next to the dermal papilla which do not express Notch-1, whereas Jagged-1 expression in the upper follicle bulb ove rlaps Notch-1 expression and correlates with bulb cell differentiation into hair shaft conical and cuticle keratinocytes. (C) 1998 Elsevier Science Ir eland Ltd. All rights reserved.