The N-Terminal Domain of GluD2 (GluRδ2) Recruits Presynaptic Terminals and Regulates Synaptogenesis in the CerebellumIn Vivo

• DOI: 10.1523/jneurosci.6013-08.2009
• Publication Date: 2009-05-06T17:33:18Z
• Authors: Wataru Kakegawa; Taisuke Miyazaki; Kazuhisa Kohda; Keiko Matsuda; Kyoichi Emi; Junko Motohashi; Masahiko Watanabe; Michisuke Yuzaki
• Keywords: Mice, Knockout; Models, Molecular; 0301 basic medicine; Analysis of Variance; Long-Term Synaptic Depression; Green Fluorescent Proteins; Gene Transfer Techniques; Excitatory Postsynaptic Potentials; Gene Expression; Motor Activity; Electric Stimulation; Motor Skills Disorders; Disease Models, Animal; Mice; 03 medical and health sciences; Animals, Newborn; Microscopy, Electron, Transmission; Cerebellum; Animals; Humans; Amino Acid Sequence; Cell Line, Transformed

The δ2 glutamate receptor (GluRδ2; GluD2), which is predominantly expressed on postsynaptic sites at parallel fiber (PF)–Purkinje cell synapses in the cerebellum, plays two crucial roles in the cerebellum: the formation of PF synapses and the regulation of long-term depression (LTD), a form of synaptic plasticity underlying motor learning. Although the induction of LTD and motor learning absolutely require signaling via the cytoplasmic C-terminal domain of GluD2, the mechanisms by which GluD2 regulates PF synaptogenesis have remained unclear. Here, we examined the role of the extracellular N-terminal domain (NTD) of GluD2 on PF synaptogenesis by injecting Sindbis virus carrying wild-type (GluD2wt) or mutant GluD2 into the subarachnoid supracerebellar space ofGluD2-null mice. Remarkably, the expression of GluD2wt, but not of a mutant GluD2 lacking the NTD (GluD2ΔNTD), rapidly induced PF synapse formation and rescued gross motor dyscoordination in adultGluD2-null mice just 1 d after injection. In addition, although the kainate receptor GluR6 (GluK2) did not induce PF synaptogenesis, a chimeric GluK2 that contained the NTD of GluD2 (GluD2NTD–GluK2) did. Similarly, GluD2wtand GluD2NTD–GluK2, but not GluD2ΔNTD, induced synaptogenesis in heterologous cellsin vitro. In contrast, LTD was restored inGluD2-null Purkinje cells expressing a mutant GluD2 lacking the NTD. These results indicate that the NTD of GluD2 is necessary and sufficient for the function of GluD2 in the regulation of PF–Purkinje cell synaptogenesis. Furthermore, our results suggest that GluD2 differently regulates PF synaptogenesis and cerebellar LTD through the extracellular NTD and the cytoplasmic C-terminal end, respectively.