Expression of acetylcholine receptor α-subunit mRNA during differentiation of the BC₃H1 muscle cell line

The accumulation of translatable acetylcholine receptor α-subunit mRNA was examined in the BC₃H1 muscle cell line in response to serum and cell growth. Relative amounts of α-subunit mRNA were quantitated during differentiation by cell-free translation and immunoprecipitation with an α-subunit-specific monoclonal antibody. Logarithmically growing cells do not possess cell surface acetylcholine receptors; however, a significant amount of α-subunit mRNA is detectable in cells under these conditions. Furthermore, α-subunit is synthesized in growing undifferentiated cells at a rate similar to that of differentiated cultures. Following growth arrest of BC₃H1 cells, surface receptors are induced to levels greater than 100-fold above that of growing cells. The relative level of translatable α-subunit mRNA in differentiated cells, however, is only approximately 4-fold greater than in growing cultures. Induction of α-subunit mRNA appears to be reversible since reinitiation of growth in quiescent differentiated BC₃H1 cells results in a reduction in relative abundance of this mRNA species to levels comparable to that of undifferentiated cells and the concomitant loss of surface receptors. These results indicate that receptor expression during differentiation is regulated both post-translationally and at the level of receptor subunit mRNA accumulation.