Local Translation of Extranuclear Lamin B Promotes Axon Maintenance

Byung C Yoon,Hosung Jung,Asha Dwivedy,Catherine M O'Hare,Krishna H Zivraj,Christine E Holt

doi:10.1016/j.cell.2011.11.064

Abstract

SummaryLocal protein synthesis plays a key role in regulating stimulus-induced responses in dendrites and axons. Recent genome-wide studies have revealed that thousands of different transcripts reside in these distal neuronal compartments, but identifying those with functionally significant roles presents a challenge. We performed an unbiased screen to look for stimulus-induced, protein synthesis-dependent changes in the proteome ofXenopus retinal ganglion cell (RGC) axons. The intermediate filament protein lamin B2 (LB2), normally associated with the nuclear membrane, was identified as an unexpected major target. Axonal ribosome immunoprecipitation confirmed translation of lb2 mRNA in vivo. Inhibition of lb2 mRNA translation in axons in vivo does not affect guidance but causes axonal degeneration. Axonal LB2 associates with mitochondria, and LB2-deficient axons exhibit mitochondrial dysfunction and defects in axonal transport. Our results thus suggest that axonally synthesized lamin B plays a crucial role in axon maintenance by promoting mitochondrial function.

Highlights

Wiring the central nervous system (CNS) requires the precise guidance of axons to distant synaptic targets and their subsequent maintenance
Subcellular Profiling using DIGE-NCAT: Identification of Cue-Induced Proteins Several genome-wide screens using axons/growth cone (GC) severed from neurons grown in culture have identified thousands of axonally localized mRNAs (Andreassi et al, 2010; Gumy et al, 2011; Taylor et al, 2009; Zivraj et al, 2010)—a puzzlingly large number to provide functionally relevant insights
We used 2D difference gel electrophoresis (2D-DIGE), a method that permits quantitative comparative analysis between two proteomes, to ask whether global proteomic differences could be detected after cue stimulation in cultured embryonic Xenopus retinal neurons. (Lilley et al, 2002)

Summary

Introduction

Wiring the central nervous system (CNS) requires the precise guidance of axons to distant synaptic targets and their subsequent maintenance. The growth cone (GC) at the tip of a growing axon and remote from the cell body encounters numerous extracellular signals to which it must promptly respond to guide the axon to its synaptic target. Developing axons possess a considerable degree of functional autonomy, and axons severed from their cell bodies can respond to guidance cues in culture (Campbell and Holt, 2001) and navigate accurately in vivo (Harris et al, 1987). This autonomous signal processing in the axon often involves rapid regulation of protein levels in the GC, which is achieved by local protein synthesis and degradation. Lamin mRNAs have recently been found in various axons (Gumy et al, 2011; Taylor et al, 2009; Zivraj et al, 2010)

Results

Discussion

Conclusion