Vitronectin and thrombospondin promote retinal neurite outgrowth: developmental regulation and role of integrins.

Extracellular matrix (ECM) glycoproteins regulate neuronal development and axonal growth. In this paper, the ECM glycoprotein vitronectin was identified and localized in the embryonic chick neuroretina. To identify potentially important neurite outgrowth-promoting molecules, responses of embryonic chick retinal neurons to vitronectin and thrombospondin, another retinal ECM constituent, were examined. These neurons were shown to attach and extend neurites on either glycoprotein. Integrins containing the alpha v or beta 1 subunits mediate both responses to vitronectin and neurite outgrowth on thrombospondin. Attachment to thrombospondin was inhibited by heparin, suggesting that neurons also utilize a proteoglycan or sulfated glycolipid as a receptor for this glycoprotein. Thus, retinal neurons use specific receptors to interact with vitronectin and thrombospondin, two glycoproteins present in the embryonic neuroretina, suggesting roles for these ligands and their receptors in retinal development.