title: Axonally synthesized β-actin and GAP-43 proteins support distinct modes of axonal growth.
abstract: Increasing evidence points to the importance of local protein synthesis for axonal growth and responses to axotomy, yet there is little insight into the functions of individual locally synthesized proteins. We recently showed that expression of a reporter mRNA with the axonally localizing β-actin mRNA 3'UTR competes with endogenous β-actin and GAP-43 mRNAs for binding to ZBP1 and axonal localization in adult sensory neurons (Donnelly et al., 2011). Here, we show that the 3'UTR of GAP-43 mRNA can deplete axons of endogenous β-actin mRNA. We took advantage of this 3'UTR competition to address the functions of axonally synthesized β-actin and GAP-43 proteins. In cultured rat neurons, increasing axonal synthesis of β-actin protein while decreasing axonal synthesis of GAP-43 protein resulted in short highly branched axons. Decreasing axonal synthesis of β-actin protein while increasing axonal synthesis of GAP-43 protein resulted in long axons with few branches. siRNA-mediated depletion of overall GAP-43 mRNA from dorsal root ganglia (DRGs) decreased the length of axons, while overall depletion of β-actin mRNA from DRGs decreased the number of axon branches. These deficits in axon growth could be rescued by transfecting with siRNA-resistant constructs encoding β-actin or GAP-43 proteins, but only if the mRNAs were targeted for axonal transport. Finally, in ovo electroporation of axonally targeted GAP-43 mRNA increased length and axonally targeted β-actin mRNA increased branching of sensory axons growing into the chick spinal cord. These studies indicate that axonal translation of β-actin mRNA supports axon branching and axonal translation of GAP-43 mRNA supports elongating growth.
authors: Department of Biological Sciences, University of Delaware, Newark, Delaware 19716, USA.
authors: Christopher J
authors: CJ
authors: Donnelly
authors: Michael
authors: M
authors: Park
authors: Mirela
authors: M
authors: Spillane
authors: Soonmoon
authors: S
authors: Yoo
authors: Almudena
authors: A
authors: Pacheco
authors: Cynthia
authors: C
authors: Gomes
authors: Deepika
authors: D
authors: Vuppalanchi
authors: Marguerite
authors: M
authors: McDonald
authors: Hak Hee
authors: HH
authors: Kim
authors: Hak Kee
authors: HK
authors: Kim
authors: Tanuja T
authors: TT
authors: Merianda
authors: Gianluca
authors: G
authors: Gallo
authors: Jeffery L
authors: JL
authors: Twiss
mesh_terms: D000199:Actins / Q000096:biosynthesis* / Q000502:physiology; D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D002642:Chick Embryo; D019922:GAP-43 Protein / Q000096:biosynthesis / Q000502:physiology*; D005727:Ganglia, Spinal / Q000254:growth & development* / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000199:Actins; D019922:GAP-43 Protein; D012333:RNA, Messenger; D034741:RNA, Small Interfering