Fig. 2.

A series of intracellular barriers is encountered by nonviral gene carriers in neurons. (A) Successful vehicles must be able to (1) associate with the neuronal plasma membrane, (2) undergo internalization, (3a) escape endosomes, and (4) deliver nucleic acids to the nucleus (a) or cytoplasm (b). (B) If vehicles arrive at the axon terminus, they must additionally undergo retrograde axonal transport (3b).