Transcriptional regulation of nicotinic acetylcholine receptor genes during muscle development.

The quantities of nicotinic acetylcholine receptors measured by alpha-bungarotoxin binding on the surface of mouse skeletal muscle C2 cells increase by approximately 10- to 100-fold during their terminal differentiation in culture. By northern blot analysis, we have determined that the steady-state levels of the AChR alpha and delta subunit mRNAs increase by approximately 15-fold during differentiation of C2 cells. To determine if the differences in message levels during myogenesis are due to changes in transcriptional rates of these genes, nuclear run-on experiments were done using nuclei from 3-day-old undifferentiated cells and 7-day-old differentiated cells. The rates of transcription for both the alpha and delta subunit genes changed from levels that could not be detected over background in nuclei from undifferentiated cells to levels that were at least 8-fold over background in differentiated nuclei. As internal controls, we measured the rates of transcription of mouse actin and histone genes. The signals obtained from both undifferentiated and differentiated nuclei were approximately 50-fold over background for both genes, indicating that the absence of detectable transcription of receptor subunit genes in undifferentiated C2 is specific.