IDENTIFICATION OF A NOVEL ISOFORM OF THE RETINOIC ACID RECEPTOR-GAMMA EXPRESSED IN THE MOUSE EMBRYO

Retinoic acid is known to have profound effects on developmental processes. It has been implicated as a putative morphogen in the developing chick limb bud and regenerating amphibian limb blastema and has been demonstrated to have powerful teratogenic effects in mammals, including humans. Recently, three specific retinoic acid receptors (RARs), RARα, -β, and -γ, were identified and shown to be members of the steroid receptor superfamily. We report the identification of a novel RARγ isoform, mRARγB, which differs from the previously described mouse RARγ at its amino terminus. In addition, we show that both RARγ isoforms are expressed maximally at midgestation in structures known to be affected adversely by retinoic acid administration to pregnant mice. Multiple RAR isoforms, each of which may play a unique or combinatorial role as a regulator of mammalian development, are thus expressed in the mouse embryo.