The Survival of Motor Neuron (SMN) Protein Interacts with the mRNA-Binding Protein HuD and Regulates Localization of Poly(A) mRNA in Primary Motor Neuron Axons

• Type of Material: Article
• Authors: Claudia Fallini, Emory University; Honglai Zhang, Albert Einstein College; Yuehang Su, Emory University; Vincenzo Silani, Università degli Studi di Milano; Robert H. Singer, Albert Einstein College; Wilfried O Rossoll, Emory University; Gary Bassell, Emory University
• Language: English
• Date: 2011-03-09
• Publisher: Lippincott, Williams & Wilkins
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2011 the authors
• Final Published Version (URL): http://www.jneurosci.org/content/31/10/3914
• Title of Journal or Parent Work: Journal of Neuroscience Nursing
• ISSN: 0888-0395
• Volume: 31
• Issue: 10
• Start Page: 3914
• End Page: 3925
• Grant/Funding Information: This work was supported by SMA Europe fellowship to CF, National Institutes of Health (NIH) grant HD055835, Spinal Muscular Atrophy Foundation and Weisman Family Foundation to GJB, and NIH grant HD056130 to WR. The Neuronal Imaging Core is supported by Emory Neuroscience NINDS Core Facilities grant, P30NS055077.
• Research Categories: Biology, Neuroscience; Biology, Cell

Abstract

Spinal muscular atrophy (SMA) results from reduced levels of the survival of motor neuron (SMN) protein, which has a well-characterized function in spliceosomal small nuclear ribonucleoprotein assembly. Currently, it is not understood how deficiency of a housekeeping protein leads to the selective degeneration of spinal cord motor neurons. Numerous studies have shown that SMN is present in neuronal processes and has many interaction partners, including mRNA binding proteins, suggesting a potential non-canonical role in axonal mRNA metabolism. In this study, we have established a novel technological approach using bimolecular fluorescence complementation (BiFC) and quantitative image analysis to characterize SMN-protein interactions in primary motor neurons. Consistent with biochemical studies on the SMN complex, BiFC analysis revealed that SMN dimerizes and interacts with Gemin2 in nuclear gems and axonal granules. In addition, using pull down assays, immunofluorescence, cell transfection, and BiFC, we characterized a novel interaction between SMN and the neuronal mRNA-binding protein HuD, which was dependent on the Tudor domain of SMN. A missense mutation in the SMN Tudor domain, which is known to cause SMA, impaired the interaction with HuD, but did not affect Smn axonal localization or self-association. Furthermore, time-lapse microscopy revealed SMN co-transport with HuD in live motor neurons. Importantly, SMN knockdown in primary motor neurons resulted in a specific reduction of both HuD protein and poly(A) mRNA levels in the axonal compartment. These findings reveal a non-canonical role for SMN whereby its interaction with mRNA binding proteins may facilitate the localization of associated poly(A) mRNAs into axons.