The Effects of Cell Surface NgCAM Expression on Developing Chick Brain Axons In Vitro

Abstract

During embryonic brain development, molecular guidance cues work in concert to transduce signals to guide axons to their appropriate targets. Of these cues are proteins of the Ig superfamily, including L1 and its chick homologue, neuron‐glia cell adhesion molecule (NgCAM). L1 and NgCAM are neuronal cell surface membrane proteins shown by others to accelerate axonogenesis and increase axon elongation. In vitro bioassays were performed in order to test the hypothesis that NgCAM expression on the cell monolayer will increase rate of outgrowth, axon length, and number of axon processes. Embryonic Day 7 optic tectum (OT) explants were first used to study outgrowth, yet failed to be an efficient and reproducible model. Aggregates were then made from dissociated OT cells and plated onto NIH3T3 monolayers that did or did not express uniform NgCAM and onto monolayers exhibiting patterned NgCAM expression. The aggregates were visualized using static images and time‐lapse microscopy by fluorescent membrane dye. Current data has shown an increase in both axon length and number in the presence of NgCAM, suggesting its crucial role as a positive axon guidance cue. Supported in part by HHMI and NIH.