Might prepatterned acetylcholine-receptor clusters on surface myotubes be a sign of neuromuscular-junction maturation failure?

Abstract

During human myogenesis and synaptogenesis, the first contact between multiaxonal nerve terminals and the primary myotube occurs at an early stage of gestation, then monoaxonal nerve terminals form and postsynaptic clusters of acetylcholine-receptor are modified and redistributed to the site of muscle-nerve contact. The aim of this study is to present the ultrastructural features of muscle and motor-junction immaturity severe enough to lead to death in the first months of life. Ultrastructural-level analysis was carried out on the quadriceps femoris muscle of an infant born at full term with severe respiratory distress but with normal SMN1 and IGHMBP2 genes. Arrested muscle maturation was manifested in the presence of primary and mature myotubes, prepatterned acetylcholine-receptor clusters devoid of terminal axons, lack of synapses and multiaxonal unmyelinated intramuscular nerves. The "naked" prepatterned clusters observed on the surface of myotubes normally never observed in neonates might be a sign of a new genetic defect in innervation.