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Different neuronal populations were used to compare the neurite outgrowth-promoting activities of N-CAM and N-cadherin expressed via gene transfer on the surface of nonneuronal cells. In contrast to a previously reported developmental loss of retinal ganglion cell re sponsiveness to N-CAM, these cells exhibited an increased and maintained responsiveness to N-cadherin over the same developmental period (E6-El l). N-CAM and N-cadherin responses could be specifically inhibited by their own antibodies, but not by antisera to the 01 integrin family or the LllG4 glycoprotein. Cerebellar neurons showed qualitative differences in the nature of the dose-response curves for transfected N-CAM expression (highly cooperative) versus N-cadherin expression (linear). In addition “subthreshold” levels of N-CAM expression, which do not normally support neurite outgrowth, did so when coexpressed with functional levels of …