The retinoic acid and retinoid X receptors are differentially expressed during myoblast differentiation.

Retinoids (all trans and 9-cis retinoic acid) are pleiotropic regulators of cell fate, and have been shown to regulate the expression of helix loop helix transcription factors (e.g MyoD, myogenin and Myf-5) that control myogenic differentiation. The effects of retinoids are mediated through the ligand dependent retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We have found that the messenger RNA transcripts encoding RAR are repressed during differentiation of C2C12 myoblasts while, conversely, RXR mRNA transcripts are induced in C2C12 myotubes. These results imply that RXRs, play a major regulatory role in differentiated muscle.