Biochemical differentiation of nascent neurite junctions: unilateral localization of adheron components

Previous work showed that adhesive contacts made by growth cone filopodia involve extracellular filaments that can be labeled with an antiserum to adherons (adhesion-promoting complexes in conditioned medium). Here, adheron antigens were found to be differentially expressed by particular cell types and synaptic layers during chick retina development, and this differential expression at the cellular level was retained in culture. When applied to living cells, adheron antibodies characteristically patched at filopodial junctions. Monospecific antibodies to purpurin and a heparan sulphate proteoglycan (HSPG), two components of adherons, labeled a subpopulation of junctions. Most interestingly, anti-purpurin and anti-HSPG bound only to one end of adhesive filaments. Such localization to discrete microdomains provides support for a heterotypic adhesive mechanism in junction formation.