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

Abstract

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-laminin and components recognized by the lectin Dolichos 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 microns 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 with Dolichos 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 with Dolichos biflorus agglutinin removed the gradient of substratum affinity around the endplate. These results indicate that the s-laminin and Dolichos 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.