CHARACTERIZATION OF CDNAS ENCODING 2 CHICK RETINOIC ACID RECEPTOR-ALPHA ISOFORMS AND DISTRIBUTION OF RETINOIC ACID RECEPTOR-ALPHA, RECEPTOR-BETA AND RECEPTOR-GAMMA TRANSCRIPTS DURING CHICK SKIN DEVELOPMENT

The amino acid sequence of the retinoic acid receptors alpha, beta and gamma (RAR alpha, beta and gamma) can be divided into six functional domains (A-F), different isoforms arising from the presence of differe nt A domains by differential splicing. In order to address the respect ive roles of the different RARs during skin morphogenesis in birds. cD NAs encoding two chick RAR alpha isoforms (alpha 1 and alpha 2) have b een isolated. While the A1 and B-F domains of the RAR alpha are highly conserved across species, the chick A2 domain contains 50% specific a mino acids. The three RAR alpha, beta and gamma genes display specific patterns of expression during chick skin morphogenesis. As in mouse, RAR alpha and gamma transcripts are present in both the dermis and epi dermis during the first stages of skin appendage formation. Furthermor e, Northern blot analysis suggests that different RAR alpha and gamma isoforms could be successively required during feather formation. The RAR gamma gene, continuously expressed in the epidermal cells in both chick and mouse, is thus likely to play a similar role in skin develop ment in these two species. however, RAR alpha transcripts, only transi ently detected during mouse skin development, still accumulate in epid ermis during the later stages of chick skin differentiation. Furthermo re. RAR beta transcripts, never detected during normal development in mouse skin, are actually present at the early stages of chick skin mor phogenesis. Thus, our results suggest that the role of the three RAR i n skin development has not been strictly conserved in the different cl asses of vertebrates.