ACETYLCHOLINESTERASE ENHANCES NEURITE GROWTH AND SYNAPSE DEVELOPMENT THROUGH ALTERNATIVE CONTRIBUTIONS OF ITS HYDROLYTIC CAPACITY, CORE PROTEIN, AND VARIABLE C-TERMINI

Accumulated indirect evidence suggests nerve growth-promoting activiti es for acetylcholinesterase (AChE). To determine unequivocally whether such activities exist, whether they are related to the capacities of this enzyme to hydrolyze acetylcholine and enhance synapse development , and whether they are associated with alternative splicing variants o i AChEm-RNA, we used four recombinant human AChEDNA vectors, When Xeno pus laevis embryos were injected with a vector expressing the synapse- characteristic human AChE-E6, which contains the exon B-encoded C term inus, cultured spinal neurons expressing this enzyme grew threefold fa ster than cocultured control neurons. Similar enhancement occurred in neurons expressing an insertion-inactivated human AChE-E6-IN protein, containing the same C terminus, and displaying indistinguishable immun ochemical and electrophoretic migration properties from AChE-E6, but i ncapable of hydrolyzing acetylcholine. In contrast, the nonsynaptic se cretory human AChE-I4, which contains the pseudointron 4-derived C ter minus, did not affect neurite growth. Moreover, no growth promotion oc curred in neurons expressing the catalytically active C-terminally tru ncated human AChE-E4, demonstrating a dominant role for the EG-derived C terminus in neurite extension. Also, AChE-E6 was the only active en zyme variant to be associated with Xenopus membranes. However, postsyn aptic length measurements demonstrated that both AChE-E6 and AChE-E4 e nhanced the development of neuromuscular junctions in vivo, unlike the catalytically inert AChE-E6-IN and the nonsynaptic AChE-14. These fin dings demonstrate an evolutionarily consented synaptogenic activity fo r AChE that depends on its hydrolytic capacity but not on its membrane association, Moreover, this synaptogenic effect differs from the grow th-promoting activity of AChE, which is unrelated to its hydrolytic ca pacity yet depends on its exon 6-mediated membrane association.