Melanophore lineage and clonal organization of the epidermis in Xenopus embryos as revealed by expression of a biogenic marker, GFP

Melanophore lineage during embryogenesis of Xenopus laevis was traced using the overexpression of a biogenic marker, green fluorescent protein (GFP). Two different approaches mere applied after injection of GFP mRNA thence a marker construct) into each blastomere at the 16-cell stage. In in vivo exp eriments, the embryos injected with a marker construct were grown until sta ge 45, in which melanophores mere distributed over the whole body and were good enough for checking GFP expression at their migratory destination. In in vitro experiments, neural tubes of the embryos injected with a marker co nstruct were isolated and cultured at stage 21 to examine by virtue of GFP expression how neural crest cells differentiate into melanophores. The resu lts obtained from both in vivo and in vitro experiments indicated the follo wing: 1) selected animal blastomeres vastly contribute to the development o f melanophores, whereas other animal blastomeres do so slightly at a limite d pace; and 2) vegetal blastomeres never contribute to melanophores in norm al development, whereas certain vegetal blastomeres have a potential to giv e rise to melanophores in vitro. The analyses using GFP also disclosed that the dorsal and ventral epidermis derive from the restricted animal blastom eres in the normal development. Since the dorso-ventrality of the epidermis has been inseparably coupled with integumental pigmentation, the clonal or ganization of the epidermis observed in the present study is discussed in t he light of pigment pattern formation attributed by melanophores.