S-laminin and N-acetylgalactosamine located at the synaptic basal lamina of skeletal muscle are involved in synaptic recognition by growing neurites

Summary The purpose of the work reported here is to identify molecular components of the synaptic basal lamina of skeletal muscle fibres which allow recognition of original synaptic sites by regenerating motor axons. We focused on s-larninin and components recognized by the lectinDolichos biflorus agglutinin previously shown to be specifically located at the synaptic basal lamina. We used a cryoculture bioassay in which chick ciliary ganglion neurons grow on rat skeletal muscle cryostat sections. In control cultures, neurites extended over the muscle sections in close association with the muscle cell surface. It was observed that most of the neurites that extended towards the endplate zone and reached an area of 40 m around the neuromuscular junction ceased to grow when they contacted the synaptic site. Masking either lectin receptors or some s-laminin molecule epitopes prior to the culture of neurons alters the behaviour of growing neurites. On sections treated either withDolichos biflorus agglutinin or anti s-laminin monoclonal antibodies (D5 and C4) most of the neurites did not stop their growth at the synaptic regions. Moreover, treating muscle sections withDolichos biflorus agglutinin removed the gradient of substratum affinity around the endplate. These results indicate that the s-laminin andDolichos biflorus agglutinin receptors present on muscle cell surfaces may play a functional role in the interaction of growing neurites with original synaptic sites in the process of neuromuscular regeneration.