Changes in fibronectin distribution in the developing peripheral nervous system of the chick.

The relationship of peripheral nerves with fibronectin was examined at different stages of the chick embryo using double immunofluorescent staining. Neurons were stained with a monoclonal antibody (E/C8) against intermediate filaments in neuronal processes, and fibronectin was stained with polyclonal antibodies. Prior to axonal outgrowth, fibronectin was distributed in a meshwork throughout the mesenchyme. However, soon after the initiation of axonal outgrowth, fibronectin began to disappear along neuronal pathways. Thus, during the period of active axonal growth, all neural tissues were marked by the striking absence of fibronectin. Interestingly, fibronectin reappeared along peripheral pathways soon after projection patterns were established. The presence of fibronectin in the substrate on which axons grow suggests that fibronectin may provide a permissive substrate for axon extension. The disappearance of fibronectin upon axon arrival suggests that neurons may modify the substrate of their pathway during outgrowth.