Transcriptional Control of Acetylcholinesterase Expression During Quail Muscle Development in Culture

Abstract

We have studied the regulation of acetylcholinesterase (AChE) expression during myoblast fusion and differentiation in tissue-cultured quail muscle. AChE synthesis increases throughout the period of cell differentiation and declines following the onset of spontaneous muscle contraction. RNase protection assays show that AChE transcripts increase 10–30 fold during the period of fusion and differentiation, then decrease as the myotubes become functionally mature. By in situ hybridization, AChE transcripts are low or undetectable in mononucleated myoblasts, highest in the newly formed myotubes, and lower in the more mature muscle fibers. Using DRB or actinomycin D to inhibit transcription, we show that the half life of AChE mRNA remains unchanged during myotube development. In contrast, the relative rate of AChE transcription, measured using nuclear run on assays, increased during differentiation and declined upon onset of muscle contraction. Inhibition of spontaneous contraction with tetrodotoxin resulted in an increased rate of AChE transcription and increased AChE mRNA levels without altering its half life. Conversely, treatment with veratridine to chronically depolarize the fibers resulted in a decreased rate of AChE transcription and lower mRNA levels. Under all conditions, the relative rate of AChE protein synthesis correlated well with the level of AChE transcripts. Together, these studies suggest that AChE expression in avian myotubes is controlled primarily at the transcriptional level.