EXPRESSION AND IN-VITRO FUNCTION OF BETA(1)-INTEGRIN LAMININ RECEPTORS IN THE DEVELOPING AVIAN CILIARY GANGLION

In chick development, ciliary ganglion (CG) neurons go through a perio d of axon extension from approximately embryonic day (E)4 to E8, follo wed by a period of synaptogenesis and neuronal cell death. By examinin g the immunohistochemical localization of laminin, in conjunction with Dil labeling of the ciliary nerve projection, we have determined that the pathway taken by these neurons is rich in laminin expression. The refore, laminins are good candidate molecules for mediating outgrowth of these neurons in vivo. In vitro, the ability of CG neurons to exten d neurites on laminin-l (EHS laminin, alpha 1 beta 1 gamma 1) is maxim al up to E8, then declines dramatically. CG neuron outgrowth on lamini n-l requires the activity of beta(1)-class integrins. We have used sub unit-specific antibodies to determine which of the five beta(1)-contai ning heterodimers known to be laminin receptors (alpha(1) beta(1), alp ha(2) beta(1), alpha(3) beta(1), alpha(5) beta(1), alpha(7) beta(1)) a re expressed, and which mediate neurite outgrowth. While we could not detect expression of alpha(2) or alpha(7), We have found that alpha(1) , alpha(3) beta(1), and alpha(6) beta(1) are expressed on the surface of ciliary ganglion neuron cell bodies and axons, both in vitro and in vivo. Furthermore, antibodies against alpha(3) and alpha(6), but not alpha(1), interfered with CG neurite outgrowth on laminin-l in vitro. Taken together, these data suggest that interactions of cell surface a lpha(3) beta(1) and alpha(6) beta(1) integrins with laminin-l are like ly to mediate growth of CG neurons during pathfinding in vivo.