MYOBLAST FUSION AND INNERVATION WITH RAT MOTOR-NERVE ALTER DISTRIBUTION OF ACETYLCHOLINESTERASE AND ITS MESSENGER-RNA IN CULTURES OF HUMAN MUSCLE

To elucidate the mechanisms underlying acetylcholinesterase (AChE) loc alization, we analyzed the distribution of AChE and Ache mRNA during m yogenesis in cocultures of human muscle and fetal rat spinal cord. We observed a temporal coincidence in alterations of AChE localization an d nuclei expressing the message, suggesting developmental regulation a t the mRNA level. Nonuniform mRNA staining among nuclei suggests async hronous regulation, also supporting an earlier proposal that transcrip tion proceeds intermittently. Asynchrony seems to be overridden by gen erally acting factors during myoblast fusion, when message is up-regul ated, and at the onset of muscle contractions, when it becomes restric ted to some nuclei in the junctional region and focal patches of AChE appear near nerve contacts. Coincidence of mRNA down-regulation and sy nthesis of stable basal lamina-bound AChE suggests coordinated adaptat ion, so that sufficient enzyme may be derived from low message levels.