POLYSIALIC ACID IN THE VERTEBRATE NERVOUS-SYSTEM - A PROMOTER OF PLASTICITY IN CELL-CELL INTERACTIONS

Polysialic acid (PSA), a homopolymer attached to the neural cell adhes ion molecule (NCAM), serves as a modulator of cell interactions, Polys ialic acid exhibits a highly regulated expression pattern. During embr yonic development its abundant expression is closely correlated with a xon pathfinding and targeting, and with certain aspects of muscle form ation. Its level also can be altered by synaptic activity. During neon atal development and in the adult brain, PSA expression is more restri cted, being primarily associated with regions capable of morphological or physiological plasticity. The ability to perturb PSA in vivo by a specific glycosidase and by the creation of NCAM-deficient mice has le d to extensive analysis of its biological function. These studies sugg est that the primary role of PSA is to promote changes in cell interac tions and thereby facilitate plasticity in the structure and function of the nervous system.