Differential expression of the rat retinoid X receptor γ gene during skeletal muscle differentiation suggests a role in myogenesis

Abstract

Even though previous studies have shown that transcripts encoding the murine retinoid X receptor γ (RXRγ) are present in skeletal muscle of mouse embryos and that cultured myoblasts are induced to differentiate upon retinoid treatment, a function for RXRγ and retinoids in mammalian myogenesis has not yet been identified. To begin to understand the possible role of RXRγ during mammalian myogenesis we isolated novel rat RXRγ cDNA sequences and examined in detail the spatio-temporal expression pattern of RXRγ transcripts in relation to skeletal muscle differentiation in rat embryos and cultured myoblasts. We show that the onset of RXRγ expression coincides with the differentiation of limb myoblasts in vivo. In vitro, RXRγ is expressed in differentiating myoblasts, but not in proliferating myoblasts. In the myotome, however, RXRγ is first expressed after myoblast differentiation, with RXRγ transcripts being confined initially to its ventral region. Subsequently, RXRγ becomes expressed throughout limb and myotome-derived muscle masses, and by the end of the primary myogenic wave, RXRγ transcripts are mainly confined to their periphery. This dynamic expression pattern of RXRγ during myogenesis suggests its possible involvement in the differentiation of limb myoblasts but excludes a role in the differentiation of early myotomal myoblasts.