9-CIS RETINOIC ACID ANTAGONIZES THE STIMULATORY EFFECT OF 1,25-DIHYDROXYVITAMIN D-3 ON CHONDROGENESIS OF CHICK LIMB BUD MESENCHYMAL CELLS -INTERACTIONS OF THEIR RECEPTORS

Retinoids or vitamin D have been found to profoundly affect pattern fo rmation and chondrogenesis in the developing limb. These substances me diate their actions through their nuclear receptors. In the present in vestigation, we present data showing that 9-cis RA, the ligand for RXR can stimulate chondrogenesis of chick limb bud mesenchymal cells, how ever, in combination, it antagonizes the stimulatory effect of vitamin D in the same system. The receptors for 9-cis RA (RXR) and vitamin D (VDR) were also shown to be present in the mesenchymal cells and to fo rm heterodimers. These results implicate these receptors in cartilage differentiation during limb development.