GROWTH CONE GUIDANCE AND NEURON MORPHOLOGY ON MICROPATTERNED LAMININ SURFACES

Neurite growth cones detect and respond to guidance cues in their loca l environment that determine stereotyped pathways during development a nd regeneration. Micropatterns of laminin (which was found to adsorb p referentially to photolithographically defined hydrophobic areas of mi cropatterns) were here used to model adhesive pathways that might infl uence 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 dep endent on the geometry of the patterned laminin, and on neuron type. D ecreasing the spacing of multiple parallel tracks of laminin alternati ng with non-adhesive tracks, resulted in decreased guidance of chick e mbryo brain neurons. Single isolated 2 mum tracks strongly guided neur ite extension whereas 2 mum tracks forming a 4 mum period multiple par allel pattern did not. Growth cones appear to be capable of bridging t he narrow non-adhesive tracks, rendering them insensitive to the small er period multiple parallel adhesive patterns. These observations sugg est that growth cones would be unresponsive to the multiple adhesive c ues such as would be presented by oriented extracellular matrix or cer tain axon fascicle structures, but could be guided by isolated adhesiv e tracks. Growth cone morphology became progressively simpler on progr essively narrower single tracks. On narrow period multiple parallel tr acks (which did not guide neurite extension) growth cones spanned a nu mber of adhesive/non-adhesive tracks, and their morphology suggests th at lamellipodial advance may be independent of the substratum by using filopodia as a scaffold. In addition to acting as guidance cues, lami nin 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 ou tgrowth whereas, on 25 mum tracks, neurite branching was reduced or ab sent, and neuron morphology was typically bipolar. These observations indicate the precision with which growth cone advance may be controlle d by substrata and suggest a role for patterned adhesiveness in neuron al morphological differentiation, but also high-light some of the limi tations of growth cone sensitivity to substratum cues.