Regional specificity of RAR gamma isoforms in Xenopus development.

All retinoic acid receptors (RAR alpha, beta, gamma) have two isoforms, whose function is unknown. We now show that at least for RAR gamma, the isoforms are differentially distributed in the embryo. RAR gamma 1 and RAR gamma 2 are detected in the head region, whereas RAR gamma 2 is the sole isoform expressed in the tail region. Specifically, it is expressed in the chordoneural hinge, a region of the tailbud that has organizing properties. Treatment with high doses of retinoic acid (RA) reduces expression in this region. The results are discussed in terms of the known teratogenic effects of RA in the tail region.