Effects of retinoic acid and Gbx1 on feather-bud formation and epidermal transdifferentiation in chick embryonic cultured dorsal skin

Abstract

Retinoic acid, an active metabolite of retinol, is known to regulate cell proliferation, differentiation, and morphogenesis during normal development of many tissues. Using chick embryonic tarsometatarsal skin, we showed previously that the expression of Gbx1, a divergent homeobox gene, is increased in the epidermis through interaction with retinol-pretreated dermal fibroblasts followed by epidermal transdifferentiation to mucous epithelium. This present study was performed to elucidate the effects of retinoic acid and Gbx1 on feather-bud formation and epidermal transdifferentiation. We showed that Gbx1 was expressed in the chick embryonic dorsal epidermis as early as at placode stage (Hamburger and Hamilton stage 31) and increased in amount during feather-bud formation. Treatment with 1 μM retinoic acid for 24 hr inhibited feather-bud formation and induced the transdifferentiation of the epidermis to a mucosal epithelium with a concomitant increase in Gbx1 mRNA expression in the epithelium. Furthermore, transient transfection of the epidermis with Gbx1 cDNA by electroporation induced elongation of the feather bud, but did not result in transdifferentiation. These results indicate that Gbx1 was involved in the feather-bud formation and was one of target genes of retinoic acid and that other signals in addition to Gbx1 were required for epidermal mucous transdifferentiation.