Are Growth Cones Lost in Translation?

Science's STKE  23 Aug 2005:
Vol. 2005, Issue 298, pp. tw305
DOI: 10.1126/stke.2982005tw305

Semaphorin 3A (Sema3A), which acts as a guidance cue to developing neurons, collapses and repels growth cones by regulating cytoskeletal dynamics, an effect that depends on intra-axonal mRNA translation. Wu et al. used in situ hybridization to screen axons in embryonic rat dorsal root ganglion (DRG) explants and found that they contained transcripts for RhoA, a small guanosine triphosphatase (GTPase) implicated in regulating cytoskeletal organization. The presence of axonal RhoA mRNA, which was also found in other types of developing neurons, was confirmed by reverse transcription polymerase chain reaction (RT-PCR). When expressed in DRG explants, transcripts that encoded destabilized enhanced green fluorescent protein (dEGFP) and contained the RhoA 3′ untranslated region (3′UTR) were targeted to axons and growth cones. Sema3A treatment enhanced RhoA abundance in the growth cones of severed axons, an effect that was blocked by inhibiting protein translation. Inactivation of RhoA with the Clostridium botulinum C3 exoenzyme, or treatment with small interfering RNA (siRNA) directed against the RhoA 5′UTR, inhibited Sema3A-mediated growth cone collapse. Whereas expression of constructs that contained RhoA and dEGFP coding sequences and the RhoA 3′UTR (and were thus targeted to axons) restored Sema3A-mediated growth cone collapse to neurons in which endogenous RhoA was knocked down with siRNA, expression of RhoA-dEGFP constructs that lacked the RhoA 3′UTR did not. Moreover, expression of a construct that enabled translation of RhoA from an internal ribosomal entry site restored Sema3A-mediated growth cone collapse to axons treated with rapamycin (which inhibits cap-dependent translation). Thus, local translation of RhoA appears to play a critical role in the regulation of growth cone collapse by Sema3A.

K. Y. Wu, U. Hengst, L. J. Cox, E. Z. Macosko, A. Jeromin, E. R. Urquhart, S. R. Jaffrey, Local translation of RhoA regulates growth cone collapse. Nature 436, 1020-1024 (2005). [PubMed]