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Gene Expression in Neurons: Seeing is Believing

Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mol. Neurosci. | doi: 10.3389/fnmol.2017.00435

Delayed degradation and impaired dendritic delivery of intron-lacking EGFP-Arc/Arg3.1 mRNA in EGFP-Arc transgenic mice

  • 1Anatomy & Neurobiology, University of California, Irvine, United States
  • 2National Institute of Environmental Health Sciences (NIH), United States
  • 3Reeve-Irvine Research Center, University of California, Irvine, United States
  • 4Department of Neurobiology & Behavior, University of California, Irvine, United States
  • 5The Solomon H Snyder Department of Neuroscience, Johns Hopkins University, United States
  • 6Department of Systems BioMedicine, National Research Institute for Child Health and Development, Japan
  • 7Medical Innovation Center, Graduate School of Medicine, Faculty of Medicine, Kyoto University, Japan
  • 8Graduate School of Medicine and Faculty of Medicine, The University of Tokyo, Japan

Arc is a unique immediate early gene (IEG) whose expression is induced as synapses are modified during learning. Newly-synthesized Arc mRNA is rapidly transported throughout dendrites and localizes near recently activated synapses. Arc mRNA levels are regulated by rapid degradation, which is accelerated by synaptic activity in a translation-dependent process. One possible mechanism is nonsense-mediated mRNA decay (NMD), which depends on the presence of a splice junction in the 3’UTR. Here, we test this hypothesis using transgenic mice that express EGFP-Arc. Because the transgene was constructed from Arc cDNA, it lacks intron structures in the 3’UTR that are present in the endogenous Arc gene. NMD depends on the presence of proteins of the exon junction complex (EJC) downstream of a stop codon, so EGFP-Arc mRNA should not undergo NMD. Assessment of Arc mRNA rundown in the presence of the transcription inhibitor actinomycin-D confirmed delayed degradation of EGFP-Arc mRNA. EGFP-Arc mRNA and protein are expressed at much higher levels in transgenic mice under basal and activated conditions but EGFP-Arc mRNA does not enter dendrites efficiently. In a physiological assay in which cycloheximide (CHX) was infused after induction of Arc by seizures, there were increases in endogenous Arc mRNA levels consistent with translation-dependent Arc mRNA decay but this was not seen with EGFP-Arc mRNA. Surprisingly, however systemic delivery of CHX did not lead to increases in Arc mRNA that have been seen in rats, suggesting that this mechanism of Arc mRNA degradation does not play a major role with behavioral induction in mice. Taken together, our results indicate: 1) Arc mRNA degradation occurs via a mechanism with characteristics of NMD; 2) rapid dendritic delivery of newly synthesized Arc mRNA after induction may depend in part on prior splicing of the 3’UTR.

Keywords: LTP; synaptic plasticity; protein synthesis; dendrite; dendritic mRNA; dendritic spines, Immediate early Gene, Nonsense-mediated decay, transcription, ArcArg3.1

Received: 18 Aug 2017; Accepted: 18 Dec 2017.

Edited by:

Sulagna Das, Albert Einstein College of Medicine, United States

Reviewed by:

Claudia Bagni, KU Leuven, Belgium
Almira Vazdarjanova, Augusta University, United States  

Copyright: © 2017 Steward, Matsudaira Yee, Farris, Salgado Pirbhoy, Worley, Okamura, Okuno and Bito. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Oswald Steward, University of California, Irvine, Anatomy & Neurobiology, Reeve-Irvine Research Center, University of California Irvine School of Medicine, Irvine, 92697, CA, United States, osteward@uci.edu