Neurotrophin-induced transport of a β-actin mRNP complex increases β-actin levels and stimulates growth cone motility

Neurotrophin regulation of actin-dependent changes in growth cone motility may depend on the signaling of beta -actin mRNA transport. Formation of an RNP complex between the beta -actin mRNA zipcode sequence and Zip-code Binding Protein 1 (ZBP1) was required for its localization to growth cones. Antisense oligonucleotides to the zipcode inhibited formation of this RNP complex in vitro and the neurotrophin-induced localization of beta -actin mRNA and ZBP1 granules. Live cell imaging of neurons transfected with EGFP-ZBP1 revealed fast, bidirectional movements of granules in neurites that were inhibited by antisense treatment, as visualized by FRAP analysis. NT-3 stimulation of P-actin protein localization was dependent on the 3'UTR and inhibited by antisense treatment. Growth cones exhibited impaired motility in the presense of antisense. These results suggest a novel mechanism to influence growth cone dynamics involving the regulated transport of mRNA.