THE RETINOIC AND RETINOID-X RECEPTORS ARE DIFFERENTIALLY EXPRESSED DURING MYOBLAST DIFFERENTIATION

Retinoids (all trans and 9-cis retinoic acid) are pleiotropic regulato rs of cell fate, and have been shown to regulate the expression of hel ix loop helix transcription factors (e.g MyoD, myogenin and Myf-5) tha t control myogenic differentiation. The effects of retinoids are media ted through the ligand dependant retinoic acid receptors (RARs) and re tinoid X receptors (RXRs). We have found that the messenger RNA transc ripts encoding RAR are repressed during differentiation of C2C12 myobl asts while, conversely, RXR mRNA transcripts are induced in C2C12 myot ubes. These results imply that RXRs, play a major regulatory role in d ifferentiated muscle.