Chick muscle cells differentiating in vitro in the absence of nerve cells produce asymmetric forms of acetylcholinesterase (AChE) only if they originate from muscles which accumulate these forms in ovo (i.e. after embryonic day 5). The presence of nerve cells does not induce the synthesis of A forms in cultures of 5 day-old myoblasts and does not increase their proportion in cultures of 7 day-old myoblasts. Thus, the capacity to synthesize (or assemble) the complex polymeric forms of AChE does

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... ot reflect a direct neural influence but might rather be considered as an intrinsic property of the c late » categories of myoblasts that sequentially occur during the differentation of leg muscles. We studied the synthesis of ChE molecular forms in the mouse muscle C 2 cell line. From these experiments we suggest that the synthesis of A forms (or their assembly) can take place as soon as the cells are withdrawn from the cell cycle, but does not require cell fusion by itself. These observations are related to other recent studies that challenge the validity of A forms as topographical/physiological markers of neuromuscular interactions. Introduction.