This project is aimed at characterizing differences in the adhesive patterns and associated growth characteristics of neuronal growth cones on defined substrates. Neurite formation by embryonic retinal ganglion cell neurons was observed using a technique (time-lapse laser scanning interference reflection microscopy) to show local distances of the cell membrane from substrates composed of purified, biologically relevant cell and substrate adhesion molecules. Members of the three major classes of adhesion molecules were tested - the calcium-dependent, calcium-independent, and the immunoglobulin superfamily of molecules. The overall degree to which growth cones bind to different molecular substrates varies widely, but a trend can be seen between reduced adhesivity and increased growth cone motility, suggesting that increasing levels of adhesivity may not be the basis of growth promotion as previously suggested. Analysis of the dynamic changes in adhesion patterns also shows wide variation among substrates. Since growth cones in vivo encounter many molecules at the same time, it seems reasonable to suggest that they must be able to integrate these many signals into a response that is suitable for directing them to their appropriate target. We suggest that there is a critical level and, perhaps, pattern of adhesion of a growth cone to its substrate that are necessary for neurites to form and move forward. Experiments will continue to analyze adhesive interactions to molecules in combination and in patterned arrays. We will also begin to investigate the role of cytoskeletal interactions with adhesion molecules on the cell surface to understand how signals in the growth cones' environment may be transduced, into behavioral responses.
