A DUAL FUNCTION ACTIVITY-DEPENDENT, MUSCLE-SPECIFIC ENHANCER FROM RATNICOTINIC ACETYLCHOLINE-RECEPTOR DELTA-SUBUNIT GENE

Nicotinic acetylcholine receptors (nAChR) mediate communication betwee n nerve and muscle. The expression of these receptors increases dramat ically during muscle development when myoblasts are fusing into multin ucleated myotubes. The molecular mechanisms mediating this muscle deve lopmental stage specific expression are not well understood. We report here the identification of nAChR delta-subunit promoter DNA sequences that differentially interact with nuclear proteins isolated from myob lasts, myotubes, and nonmuscle cells. The functional role these sequen ces play in mediating muscle specific expression was explored using mu tagenesis and enhancer assays. These studies resulted in the identific ation of a 47-bp muscle-specific enhancer that mediates increased expr ession of the nAChR delta-subunit gene during myotube formation. This enhancer contains an E-box and an element with similarity to the SV40 core enhancer (SVCE). Point mutations throughout this 47-bp enhancer s howed that the E-box and the SVCE sequence are both necessary for conf erring muscle-specific expression onto a heterologous promoter. Intere stingly, this same DNA sequence also functions as an activity-dependen t enhancer. (C) 1996 John Wiley & Sons, Inc.