Immunocytochemical localization of a cell adhesion molecule, integrin α5β1, in nerve growth cones

Abstract

It is well-known that nerve growth cones, the growing tips of nerves, play a central role in determining the direction taken by regenerating peripheral nerves though neurotropism and contact guidance. In order to identify the molecules expressed on growth cones that are responsible for contact guidance, we investigated the possible involvement of integrins as sensors for the extracellular matrix. In cultured rat PC-12i cells and chick dorsal root ganglion cells, we found that integrin α5β1 was concentrated in the filopodia and central regions of the growth cones. These integrin α5β1-rich regions corresponded well with the sites where the growth cones came into contact with and adhered to the extracellular matrix. Integrin α5β1 has been reported to bind with fibronectin in the extracellular matrix. When examined by triple staining and confocal laser scanning microscopy, we found that the distribution of integrin α5β1 in the growth cones was very similar to that of actin filaments. Integrin α5β1 was also expressed by Schwann cells. On immuno-electron microscopy, integrin α5β1 was also identified in regenerating axons in vivo. These results suggest that integrin α5β1 expressed on growth cones may function as a sensor for the extracellular matrix and Schwann cells, and thus mediate functionally important interactions in the development and regeneration of peripheral nerves.