AUTHOR=Steward Oswald , Matsudaira Yee Kelly , Farris Shannon , Pirbhoy Patricia S. , Worley Paul , Okamura Kohji , Okuno Hiroyuki , Bito Haruhiko 

TITLE=Delayed Degradation and Impaired Dendritic Delivery of Intron-Lacking EGFP-Arc/Arg3.1 mRNA in EGFP-Arc Transgenic Mice

JOURNAL=Frontiers in Molecular Neuroscience

VOLUME=10

YEAR=2018

URL=https://www.frontiersin.org/journals/molecular-neuroscience/articles/10.3389/fnmol.2017.00435

DOI=10.3389/fnmol.2017.00435

ISSN=1662-5099

ABSTRACT=<p><italic>Arc</italic> is a unique immediate early gene (IEG) whose expression is induced as synapses are modified during learning. Newly-synthesized <italic>Arc</italic> mRNA is rapidly transported throughout dendrites and localizes near recently activated synapses. <italic>Arc</italic> 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 <italic>EGFP-Arc</italic>. Because the transgene was constructed from <italic>Arc</italic> cDNA, it lacks intron structures in the 3′UTR that are present in the endogenous <italic>Arc</italic> gene. NMD depends on the presence of proteins of the exon junction complex (EJC) downstream of a stop codon, so <italic>EGFP-Arc mRNA</italic> should not undergo NMD. Assessment of <italic>Arc</italic> mRNA rundown in the presence of the transcription inhibitor actinomycin-D confirmed delayed degradation of <italic>EGFP-Arc</italic> mRNA. <italic>EGFP-Arc</italic> mRNA and protein are expressed at much higher levels in transgenic mice under basal and activated conditions but <italic>EGFP-Arc</italic> mRNA does not enter dendrites efficiently. In a physiological assay in which cycloheximide (CHX) was infused after induction of <italic>Arc</italic> by seizures, there were increases in endogenous <italic>Arc</italic> mRNA levels consistent with translation-dependent <italic>Arc</italic> mRNA decay but this was not seen with <italic>EGFP-Arc</italic> mRNA. Taken together, our results indicate: (1) <italic>Arc</italic> mRNA degradation occurs via a mechanism with characteristics of NMD; (2) rapid dendritic delivery of newly synthesized <italic>Arc</italic> mRNA after induction may depend in part on prior splicing of the 3′UTR.</p>