Characterization of cDNAs encoding the chick retinoic acid receptor γ2 and preferential distribution of retinoic acid receptor γ transcripts during chick skin development

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Abstract
Retinoic acid receptors α, β and γ (RARα, β and γ) are ligand‐inductible transcriptional activators which belong to the steroid/thyroid hormone receptor superfamily. At least two major isoforms (1 and 2) of each RAR arise by differential use of two promoters and alternative splicing. In mouse, the three RAR genes are expressed in stage‐ and tissue‐specific patterns during embryonic development. In order to understand the role of the different RARs in chick, RARγ2 cDNAs were isolated from an 8.5‐day (stage 35 of Hamburger and Hamilton) chick embryo skin library. The deduced chick RARγ2 amino acid sequence displays uncommon features such as 21 specific amino acid replacements, 12 of them being clustered in the amino‐terminal region (domains A2 and B), and a truncated acidic carboxy‐terminal region (F domain). However, the pattern of RARγ expression in chick embryo resembles that reported in mouse, particularly in skin where RARγ expression occurs in both the dermal and epidermal layers at the beginning of feather formation, and is subsequently restricted to the differentiating epidermal cells. Northern blot analysis suggests that different RARγ isoforms could be successively required during chick development.