Localisation of members of the notch system and the differentiation of vibrissa hair follicles: Receptors, ligands, and fringe modulators

Hair vibrissa follicle morphogenesis involves several cell segregation phas es, in the dermis as well as in the epidermis. The expression of Notch-rela ted genes, which are well established mediators of multiple cell segregatio n events in Drosophila development, was studied by in situ hybridisation du ring embryonic mouse vibrissa follicle morphogenesis and the first adult ha ir cycle. The results show that two receptors, Notch1 and -2, three ligands , Delta1, Serrate1, and -2, and the three Fringe regulators, Lunatic, Manic , and Radical, are expressed in different locations and morphogenetic stage s. First, the appearance of hair vibrissa primordia involves the expression of complementary patterns of Notch2, Delta1, and Lunatic Fringe in the der mis and of Notch1, Serrate2, and Lunatic Fringe in the epidermis. Second, t his expression pattern is no longer found after stage 3 in the dermis. Mean while, in the epidermis, the expression of Notch1, Serrate2, and Lunatic Fr inge before the formation of the placode may be involved in determining two populations of epidermal cells in the developing follicle. Third, compleme ntary expression patterns for Notch1, Manic, and Lunatic Fringe, as well as Serrate1 and -2 as previously shown (Powell et al., 1998), are progressive ly established from stage 4 of embryonic development both in the outer root sheath and in the hair matrix. These patterns are consistent with the one found in the adult anagen phase. During the hair vibrissa cycle, Notch1 and Manic Fringe display temporal and spatial changes of expression, suggestin g that they may intervene as modulators of trichocyte activities. (C) 2000 Wiley-Liss, Inc.