MORPHOGENETIC EFFECTS OF 9-CIS-RETINOIC ACID ON THE REGENERATING LIMBS OF THE AXOLOTL

9-cis-retinoic acid has recently been found to be a high affinity liga nd for the retinoic X receptor (RXR). RXRs are believed to be involved in metabolic activities rather than in morphogenetic ones. Interestin gly, RXR has been found to form heterodimers involving other receptors from the steroid family, such as the thyroid hormone receptor, vitami n D receptor or retinoic acid receptors (RARs). In this paper we exami ned whether or not 9-cis-retinoic acid had any morphogenetic propertie s on the regenerating axolotl limb. It is shown that 9-cis-retinoic ac id proximalized regenerating limbs and was somewhat more potent in thi s action than all-trans-retinoic acid. Based on these observations, th e possible roles of other receptors during pattern formation is discus sed.