The Expression of Two Splice Variants of Metabotropic Glutamate Receptor Subtype 5 in the Rat Brain and Neuronal Cells During Development

Abstract

We previously reported that a variant with extra amino acid residues exists in the metabotropic glutamate receptor subtype 5 (mGluR5). Either of the two isoforms, named mGluR5b and mGluR5a for the isoforms with and without the inserted sequence, respectively, generated Ca2+‐activated Cl− current when expressed in Xenopus oocytes. We herein report that these two isoforms are produced by the alternative splicing of the exon skipping type. When examined during the course of postnatal development, the major mGluR5 isotype mRNA was observed to switch from mGluR5a to mGluR5b in the rat hippocampus and the cerebral cortex. We also investigated two cell lines that could be differentiated into neuron‐like cells in vitro. Whereas the mGluR5b mRNA was hardly detectable in either undifferentiated or differentiated NG108‐15 cells, the relative amounts of the two variant mRNAs changed after the induction of differentiation in the P19 cells. An extracellular application of trans‐d,l‐1‐amino‐1,3‐cyclopentanedicarboxylate on the neuron‐like P19 cells induced intracellular Ca2+ mobilization, thus suggesting that the cells could express functional mGluR(s) coupled to phospholipase C and other components that could mediate the signal transduction pathway. This cell line may thus provide a model system for studying both mGluR5 expression and other mGluR‐induced phenomena at the molecular level.

Freshly isolated astrocyte (FIA) preparations: A useful single cell system for studying astrocyte properties

“…Interestingly at an intermediate age period, P11-20, about 75% of the cells containing the receptors also co-expressed both variants, whereas at the earlier or later time periods none of the cells co-expressed the two variants. In situ, mGluR5b increases and mGluR5a decreases with increasing age with the switch occurring somewhere between 7 and 14 days (Minakami et al, 1995). Our data suggests that this could be due to astrocytes as well as neurons.…”

Quantitative Analysis Reveals Multiple Mechanisms of Allosteric Modulation of the mGlu5 Receptor in Rat Astroglia

“…To achieve this, we first examined the interaction of NAMs and PAMs at the MPEP site on the mGlu5 receptor using 3 H]MPEP binding sites in G5 supplement-differentiated rat cortical astrocytes approximated that found in adult rat cerebral cortex; however, it should be noted that the major splice variant expressed in the former is the mGlu5a (Biber et al, 1999), whereas mGlu5b is likely to predominate in the latter (Minakami et al, 1995). The NAMs MPEP and M-5MPEP, and the neutral allosteric modulator 5-MPEP, all competed for the [ 3 H]MPEP binding site in membrane preparations from rat cortical astrocytes and cerebral cortex and defined identical levels of specific binding.…”

Gene Structure of the Human Metabotropic Glutamate Receptor 5 and Functional Analysis of Its Multiple Promoters in Neuroblastoma and Astroglioma Cells

“…Functional Implications-Transcription of GRM5 has been shown to undergo developmental regulation (10,53,58). In the early post-natal periods both transcripts and proteins of mGluR5 are markedly down-regulated in numerous brain areas, and this was shown to affect both exon IA-and exon IB-containing mRNAs in the rat brain (10).…”