RETINOIC ACID AND MOUSE SKIN MORPHOGENESIS .2. ROLE OF EPIDERMAL COMPETENCE IN HAIR GLANDULAR METAPLASIA

Retinoic acid (RA) has marked effects on mouse upper-lip skin morphoge nesis, leading to the development of glomerular gland instead of hair vibrissa follicle, but does not apparently change the dorsal pelage ha ir developmental program. In order to test the hypothesis that an up-r egulation of the beta retinoic acid nuclear receptor (RAR beta) may be implicated in the alteration of the dermal-epidermal interactions whi ch occur during cutaneous appendage development, RA-treated and untrea ted skin explants, controls as well as heterotopic recombinants, were made among nasal, upper-lip, and dorsal mouse embryonic tissues. They were analyzed by in situ hybridization with RAR beta S-35-labeled prob e after 48 hr of in vitro culture as well as by identification of the morphological phenotype of cutaneous appendages after 6 additional day s of culture on the chick chorioallantoic membrane. The results show t hat only mesenchyme from the facial region can express the RAR beta ge ne either normally or after RA treatment, depending on its nasal or up per-lip origin. However, the RAR beta up-regulation is unrelated to ha ir glandular metaplasia, which depends both on a glandular bias of the upper-lip epidermis and on the weakening of hair follicle-inducing de rmal properties. The latter occurs in both the upper-lip and dorsal de rmis as a consequence of RA treatment. (C) 1994 Academic Press, Inc.