NERVE-INDUCED DISRUPTION AND REFORMATION OF BETA(1)-INTEGRIN AGGREGATES DURING DEVELOPMENT OF THE NEUROMUSCULAR-JUNCTION

The earliest biochemical change detected during synaptogenesis is a lo cal elimination of muscle basal lamina proteins. To explore whether th is provides signal(s) that regulate postsynaptic differentiation, we e xamined the effects of innervation on the distribution of beta(1)-inte grins, which were initially present in scattered aggregates complexed with basal lamina ligands. These PI-integrin aggregates disappear alon g paths of nerve contact as their basal lamina ligands are eliminated. New accumulations of these proteins then form during assembly of the postsynaptic apparatus. The new beta(1)-integrin aggregates at develop ing synapses form partly via a redistribution of mobile molecules on m uscle surface. We thus consider whether (a) the removal of integrins' basal lamina ligands alters their cytoplasmic ligand-interactions, cau sing the dissociation of integrin clusters, and (b) this receptor modu lation helps to transduce local changes in pericellular protease activ ity into cytoplasmic signals that control postsynaptic differentiation . (C) 1997 Elsevier Science Ireland Ltd.