Expression of the A(12) form of acetylcholinesterase by developing avian leg muscle cells in vivo and during differentiation in primary cell cultures.

The accumulation of the molecular forms of acetylcholinesterase (AChE) has been studied in leg muscles during embryonic chick development and in cell cultures initiated with myoblasts obtained from embryos at different stages of development. The collagen-tailed, A(12) form appears in leg muscles as soon as day 5 in ovo. An early excision of the lumbar zone of the neural tube at day 2 1 2 in ovo severely delayed the morphological development. In leg muscles dissected at day 12 in ovo from operated embryos, we found that the total amount of AChE activity and particularly the proportion of A(12) form were dramatically reduced. Muscle cells were grown in vitro in a medium supplemented with fetal calf serum. In these conditions, chick muscle cells unequivocally synthesize the A(12) form when they originated from muscles which accumulated this form in vivo. In contrast, myoblasts obtained from 5-day old embryo leg muscles did not produce the A(12) form either in aneural cultures or in the presence of nerve cells. In relation with previous observations concerning chick myogenesis, we discuss the possibility that this difference reflects the existence of two types of myoblasts. This hypothesis would also explain the results of cocultures performed with nerve cells and normal or demedullated leg muscle myoblasts.