Cloning and characterization of alternative mRNA forms for the rat metabotropic glutamate receptors mGluR7 and mGluR8

Abstract

Novel mRNA isoforms for two members of the group III metabotropic glutamate receptors (mGluRs), called mGluR7b and mGluR8b, were identified from rat brain cerebral cortex and hippocampus. In both cases, the alternative splicing is generated by a similar out-of-frame insertion in the carboxyl-terminus that results in the replacement of the last 16 amino acids of mGluR7 and mGluR8 by 23 and 16 different amino acids, respectively. Distribution analysis for mGluR7 and mGluR8 isoforms revealed that the two splice variants are generally coexpressed in the same brain areas. The few exceptions were the olfactory bulb, in which only the mGluR7a form could be detected by reverse transcription-polymerase chain reaction, and the lateral reticular and ambiguous nuclei, which showed only mGluR8a labelling. Despite expression in the same regions, different mRNA abundance for the two variants of each receptor were observed. When transiently coexpressed in HEK 293 cells with the phospholipase C-activating chimeric G alpha qi9-G-protein, the a and b forms for both receptor subtypes showed a similar pharmacological profile. The rank order of potencies for both was: DL-amino-4-phosphonobutyrate > L-serine-O-phosphate > glutamate. However, the agonist potencies were significantly higher for mGluR8a, b compared with mGluR7a,b. In Xenopus oocytes, glutamate evoked currents only with mGluR8 when coexpressed with Kir 3.1 and 3.4. Glutamate-induced currents were antagonized by the group II/III antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine. In conclusion, the two isoforms of each receptor have identical pharmacological profiles when expressed in heterologous systems, despite structural differences in the carboxyl-terminal domains.

Regulation of Metabotropic Glutamate Receptor 7 (mGluR7) Internalization and Surface Expression by Ser/Thr Protein Phosphatase 1

“…There is an out-of-frame insertion before the last exon of the mGluR7 gene, resulting in alternative spliced isoforms, mGluR7a and mGluR7b. Therefore, 16 amino acids of mGluR7a and 23 amino acids of mGluR7b differ in their extreme C-terminal tails (31,32). Previous studies showed that PP1␥1 directly interacts with mGluR7b, but not mGluR7a, as determined using GST pulldown assays or yeast two-hybrid system interactions (33)(34)(35).…”

Metabotropic Glutamate Receptor 8-Expressing Nerve Terminals Target Subsets of GABAergic Neurons in the Hippocampus

“…We revealed the firing pattern of one of the major mGluR8 recipient neurons, the trilaminar cell that heavily innervates the subiculum in addition to the CA1 area. We also provide the first account for the immunolocalization of the other full-length alternatively spliced receptor isoform, mGluR8b (Corti et al, 1998).…”

“…To assess the specificity of the mGluR8 isoform-specific antibodies, cDNAs encoding rat mGluR8a and mGluR8b (Corti et al, 1998) were subcloned into the eukaryotic expression vector pcDNA3 (Invitrogen, San Giuliano Milanese, Italy) and transfected into subconfluent CHO-K1 cells grown in DMEM (Life Technologies, Paisley, UK) in the presence of 10% fetal bovine serum. Transfections were performed with a solution containing 10 g of cDNA and a 3:1 ratio of FuGene reagent (Roche Diagnotics, Rotkreuz, Switzerland) in 200 l of serum-free DMEM per 10 cm dish for 30 min.…”

“…The aim of the present study has been the definition of the precise distribution of mGluR8 splice variants (Corti et al, 1998) in the hippocampus in relation to synaptic sites and the characterization of the neurochemical nature of the target neurons receiving mGluR8-expressing inputs. In addition, we report the network-related firing patterns of an interneuron that belongs to a nonpyramidal cell class selectively targeted by mGluR8a-containing boutons.…”

The C Terminus of the Metabotropic Glutamate Receptor Subtypes 2 and 7 Specifies the Receptor Signaling Pathways

“…Strikingly, the variable part in GPCR splicing, including the class of mGlu receptors (12), is their C-terminal domain. For example, the natural mGlu7a receptor splice variant, mGluR7b, is generated by an out-of-frame insertion in the C terminus that results in the replacement of the last 16 amino acids of the mGlu7a receptor by 23 different amino acids (45,46). According to our finding that the C terminus of mGlu receptors plays a key role in the receptor coupling to specific effectors, different mGlu receptor splice variants could lead to different signaling pathways, depending on the splice site choice.…”