Characterization of cDNAs encoding two chick retinoic acid receptor α isoforms and distribution of retinoic acid receptorα, β and γ-transcripts during chick skin development

Abstract

The amino acid sequence of the retinoic acid receptors α, β and γ (RARα, β and γ) can be divided into six functional domains (A-F), different isoforms arising from the presence of different A domains by differential splicing. In order to address the respective roles of the different RARs during skin morphogenesis in birds, cDNAs encoding two chick RARα isoforms (α1 and α2) have been isolated. While the A1 and B-F domains of the RARα are highly conserved across species, the chick A2 domain contains 50% specific amino acids. The three RARα, β and γ-genes display specific patterns of expression during chick skin morphogenesis. As in mouse, RARα and γ transcripts are present in both the dermis and epidermis during the first stages of skin appendage formation. Furthermore, Northern blot analysis suggests that different RARα and γ isoforms could be successively required during feather formation. The RARγ gene, continuously expressed in the epidermal cells in both chick and mouse, is thus likely to play a similar role in skin development in these two species. However, RARα transcripts, only transiently detected during mouse skin development, still accumulate in epidermis during the later stages of chick skin differentiation. Furthermore, RARβ transcripts, never detected during normal development in mouse skin, are actually present at the early stages of chick skin morphogenesis. Thus, our results suggest that the role of the three RAR in skin development has not been strictly conserved in the different classes of vertebrates.