Neurite growth cones detect and respond to guidance cues in their local environment that determine stereotyped pathways during development and regeneration. Micropatterns of laminin (which was found to adsorb preferentially to photolithographically defined hydrophobic areas of micropatterns) were here used to model adhesive pathways that might influence neurite extension. The responses of growth cones were determined by the degree of guidance of neurite extension and also by examining growth cone morphology. These parameters were found to be strongly dependent on the geometry of the patterned laminin, and on neuron type. Decreasing the spacing of multiple parallel tracks of laminin alternating with non-adhesive tracks, resulted in decreased guidance of chick embryo brain neurons. Single isolated 2 microns tracks strongly guided neurite extension whereas 2 microns tracks forming a 4 microns period multiple parallel pattern did not. Growth cones appear to be capable of bridging the narrow non-adhesive tracks, rendering them insensitive to the smaller period multiple parallel adhesive patterns. These observations suggest that growth cones would be unresponsive to the multiple adhesive cues such as would be presented by oriented extracellular matrix or certain axon fascicle structures, but could be guided by isolated adhesive tracks. Growth cone morphology became progressively simpler on progressively narrower single tracks. On narrow period multiple parallel tracks (which did not guide neurite extension) growth cones spanned a number of adhesive/non-adhesive tracks, and their morphology suggests that lamellipodial advance may be independent of the substratum by using filopodia as a scaffold. In addition to acting as guidance cues, laminin micropatterns also appeared to influence the production of primary neurites and their subsequent branching. On planar substrata, dorsal root ganglion neurons were multipolar, with highly branched neurite outgrowth whereas, on 25 microns tracks, neurite branching was reduced or absent, and neuron morphology was typically bipolar. These observations indicate the precision with which growth cone advance may be controlled by substrata and suggest a role for patterned adhesiveness in neuronal morphological differentiation, but also highlight some of the limitations of growth cone sensitivity to substratum cues.
Growth cone morphology and trajectory in the lumbosacral region of the chick embryo
