Growth cone interactions with purified cell and substrate adhesion molecules visualized by interference reflection microscopy.

The migration of growth cones on substrates consisting of naturally occurring cell adhesion molecules has been extensively studied in cell culture. However, relatively little is known about how growth cones contact the substrate or how the patterns of contact change as growth cones move forward. We have examined the interactions of chick retinal ganglion cell growth cones with laminin, merosin, N-cadherin, L1 and poly-L-lysine by time-lapse interference reflection microscopy (IRM) using a laser scanning confocal microscope. In images obtained by IRM, areas of a cell that are closely apposed to the substrate appear dark whereas areas that are farther away appear light. Growth cones on Jaminin and merosin were almost uniformly light, indicating that very little of the membrane was in close contact with the substrate. Growth cones on N-cadherin had a mottled appearance with some relatively large dark gray areas. The proximal portions of filopodia often were dark, in contrast to those on laminin and merosin which were light. In addition, growth cones on N-cadherin had numerous dark gray punctate regions of close association with the substrate. Growth cones on L1 had darker regions than growth cones on other substrates and these comprised a larger fraction of their area. There also were differences in the temporal dynamics of growth cone interactions with different substrates and these differences correlated with differences in rates of growth. None of the contacts observed in growth cones were as dark or stable as focal contacts of fibroblasts.