Chemico-Biological Interactions 157–158 (2005) 29–35 Expression and distribution of acetylcholinesterase among the cellular components of the neuromuscular junction formed in human myotube in vitro Katarina Mis a , Tomaz Mars a , Marko Jevsek a , Helena Strasek a , Marko Golicnik b , Janez Brecelj c , Rado Komel b , Michael P. King d , Armand F. Miranda e , Zoran Grubic a,* a Laboratory for Molecular Neurobiology, Institute of Pathophysiology, Medical Faculty, School of Medicine, University of Ljubljana, Zaloska 4, 1000 Ljubljana, Slovenia b Institute of Biochemistry, Medical Faculty, University of Ljubljana, Slovenia c Clinical Hospital for Orthopedics, Ljubljana, Slovenia d Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, USA e Department of Neurology, College of Physicians and Surgeons, Columbia University, NY, USA Available online 26 October 2005 Abstract The results of our recent investigations on the expression and distribution of acetylcholinesterase (EC. 3.1.1.7, AChE) in the experimental model of the in vitro innervated human muscle are summarized and discussed here. This is the only model allowing studies on AChE expression at all stages of the neuromuscular junction (NMJ) formation in the human muscle. Since it consists not only of the motor neurons and myotubes but also of glial cells, which are essential for the normal development of the motor neurons, NMJs become functional and differentiated in this system. We followed AChE expression at various stages of the NMJ formation and in the context of other events characteristic for this process. Neuronal and muscular part were analysed at both, mRNA and mature enzyme level. AChE is expressed in motor neurons and skeletal muscle at the earliest stages of their development, long before NMJ starts to form and AChE begins to act as a cholinergic component. Temporal pattern of AChE mRNA expression in motor neurons is similar to the pattern of mRNA encoding synaptogenetic variant of agrin. There are no AChE accummulations at the NMJ at the early stage of its formation, when immature clusters of nicotinic receptors are formed at the neuromuscular contacts and when occasional NMJ-mediated contractions are already observed. The transformation from immature, bouton-like neuromuscular contacts into differentiated NMJs with mature, compact receptor clusters, myonuclear accumulations and dense AChE patches begins at the time when basal lamina starts to form in the synaptic cleft. Our observations support the concept that basal lamina formation is the essential event in the transformation of immature neuromuscular contact into differentiated NMJ, with the accumulation of not only muscular but also neuronal AChE in the synaptic cleft. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Acetylcholinesterase; Neuromuscular junction; Human muscle; Basal lamina; Agrin; Synaptogenesis * Corresponding author. Tel.: +386 1 543 7038; fax: +386 1 543 7021. E-mail address: Zoran.Grubic@mf.uni-lj.si (Z. Grubic). 1. Introduction Most of our present knowledge about expression, pro- cessing, targeting and turnover of cholinesterases in the 0009-2797/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cbi.2005.10.003