Rescue of abnormal phenotypes of the δ2 glutamate receptor-null mice by mutant δ2 transgenes

The δ2 glutamate receptor (GluR52) has a crucial role in cerebellar functions; disruption of GluRδ2 alleles in mice (δ2^-/-) impairs synapse formation and long-term depression, which is thought to underlie motor learning in the cerebellum, and consequently leads to motor discoordination. However, it has been unclear whether GluRδ2 is activated by glutamate analogues. Here we introduced a GluRδ2 transgene, which had a mutation (Arg514Lys) in the putative ligand-binding motif conserved in all mammalian ionotropic glutamate receptors (iGluRs) and their ancestral bacterial periplasmic amino-acid-binding proteins, into δ2^-/- mice. Surprisingly, a mutant GluRδ2 transgene, as well as a wild-type GluRδ2 transgene, rescued all abnormal phenotypes of δ2 ^-/- mice. Therefore, these results indicate that the conserved arginine residue, which is crucial for the binding of iGluRs to glutamate analogues, is not essential for the restoration of GluRδ2 functions in δ2^-/- mice.