Tenascin glycoproteins in neural pattern formation: facets of a complex picture

It is generally accepted that neuron-glia interactions play an important role in the regulation of neural development. For example, astrocytes are thought to guide migrating neuronal precursors and advancing growth cones to their destination. In addition, astrocytes have recently been ascribed a function in the segregation of forming neuronal assemblies and fiber tracts and are believed to hinder regeneration of lesioned adult central nervous system (CNS) structures. Therefore molecules that might specifically mediate neuron-glia interactions in the CNS attract considerable interest. The growing family of tenascin glycoproteins may play a key role in this context. Tenascin glycoproteins are transiently expressed by astrocytes in the nervous system and affect neuronal morphogenesis and behavior in definable ways. The present review discusses functional properties and examines seemingly contradictory effects of these extracellular matrix constituents.