DIFFERENTIAL EXPRESSION OF THE RAT RETINOID-X-RECEPTOR GAMMA-GENE DURING SKELETAL-MUSCLE DIFFERENTIATION SUGGESTS A ROLE IN MYOGENESIS

Even though previous studies have shown that transcripts encoding the murine retinoid X receptor gamma (RXR gamma) are present in skeletal m uscle of mouse embryos and that cultured myoblasts are induced to diff erentiate upon retinoid treatment, a function for RXR gamma and retino ids in mammalian myogenesis has not yet been identified. To bean to un derstand the possible role of RXR gamma during mammalian myogenesis we isolated novel rat RXR gamma cDNA sequences and examined in detail th e spatio-temporal expression pattern of RXR gamma transcripts in relat ion to skeletal muscle differentiation in rat embryos and cultured myo blasts, We show that the onset of RXR gamma expression coincides with the differentiation of limb myoblasts in vivo, In vitro, RXR gamma is expressed in differentiating myoblasts, but not in proliferating myobl asts, In the myotome, however, RXR gamma is first expressed after myob last differentiation, with RXR gamma transcripts being confined initia lly to its ventral region, Subsequently, RXR gamma becomes expressed t hroughout limb and myotome-derived muscle masses, and by the end of th e primary myogenic wave, RXR gamma transcripts are mainly confined to their periphery, This dynamic expression pattern of RXR gamma during m yogenesis suggests its possible involvement in the differentiation of Limb myoblasts but excludes a role in the differentiation of early myo tomal myoblasts. (C) 1997 Wiley-Liss, Inc.