The C-terminus of NMDAR GluN1-1a Subunit Translocates to Nucleus and Regulates Synaptic Function.

Liang Zhou,Jingjing Duan

doi:10.3389/fncel.2018.00334

Liang Zhou, Jingjing Duan

Open Access

https://doi.org/10.3389/fncel.2018.00334

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Abstract

NMDARs, the Ca2+ permeable channels, play central roles in synaptic plasticity, brain development, learning, and memory. NMDAR binding partners and associated signaling has been extensively studied in synapse-to-nucleus communications. However, whether NMDARs could directly regulate synapse-to-nucleus communications is largely unknown. Here, we analyze the four alternative splicing of the C-terminus isoforms of GluN1 (1a, 2a, 3a, and 4a), and find that C1 domain of GluN1 is necessary for nuclear localization. Besides, we find that the 10 basic amino acids in C1 domain determine the nuclear localization of GluN1 C-terminus. Further investigating the expression patterns of the full length of GluN1 four isoforms shows that only GluN-1a exhibits the cytoplasmic and nucleus distribution in primary hippocampal neurons. Electrophysiological analyses also show that over-expression of GluN1 C-terminus without C1 domain doesn't affect synaptic transmission, whereas GluN1 C-terminus containing C1 domain potentiates NMDAR-mediated synaptic transmission. Our data suggested that the 10 basic amino acids in C1 domain determine translocation of GluN1 C-terminus into nucleus and regulate synaptic transmission.

Highlights

NMDA receptors (NMDARs) are ionotropic glutamate receptors, which are important for neuronal development, synaptic plasticity, learning, and memory (Tsien et al, 1996)
Our previous study shows the C-terminus of GluN1 play a crucial role in GABAergic synapses formation (Gu et al, 2016b), indicating that the C-terminus of GluN1 is important for NMDARs-mediated biological functions
Given that single GluN1 subunit could not form the functional NMDARs in Human embryonic kidney 293A (HEK293A) cells (Cao et al, 2011; Hansen et al, 2014), we transfected GluN1 and GluN2A subunits in HEK293A cells to examine whether GluN2 is required for the translocation of GluN1-1a C terminus, the results showed the full-length GluN1-1a still showed cytoplamic distribution in HEK293A cells (Supplementary Figure S3), which suggests that the intrinsic genetic determinants of neuronal form determine the translocation of GluN1 C-terminus to nucleus in primary hippocampal neurons

Summary

Introduction

NMDA receptors (NMDARs) are ionotropic glutamate receptors, which are important for neuronal development, synaptic plasticity, learning, and memory (Tsien et al, 1996). The NMDARs are composed of two GluN1 and two GluN2/3 subunits, which are located at excitatory synapses (Paoletti et al, 2013). The GluN1-1a is the dominant isoform (Laurie and Seeburg, 1994), and the expression levels of GluN1 isoforms are regulated by synaptic activity (Mu et al, 2003; Paoletti et al, 2013). The synaptic activity modulates the immediate early genes (IEGs) expression in the nucleus (Yang et al, 2014), which is called synapse-to-nucleus communication (Deisseroth et al, 1996, 2003). The synapse-to-nucleus communication is essential for learning and memory (Lim et al, 2017). NMDARs antagonist can block synaptic activation induced IEGs expressions, which demonstrates NMDARs are required for synapse-to-nucleus communication (Mokin and Keifer, 2005; Lonergan et al, 2010).

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