Characterization of three novel isoforms of the metabotrobic glutamate receptor 7 (GRM7)

The G protein-coupled metabotropic glutamate receptors (GRMs) consist of a family of eight members. Structural and functional diversity of this receptor family is achieved by the existence of alternative exon usage generally affecting the immediate carboxy-terminus. This region is known to specifically interact with defined proteins thus mediating various receptor functions such as intracellular signal transduction, axonal targeting and synaptic clustering. For GRM7 two isoforms, GRM7_v1 and GRM7_v2, have previously been characterized. In the present study, we have identified additional splicing variants involving the 3' end of the GRM7 coding sequence and resulting in three putative novel isoforms, termed GRM7_v3, GRM7_v4, GRM7_v5. While most variants are expressed in brain and retina with varying abundance, expression of GRM7 isoforms in non-neuronal tissues appears to be restricted to isoforms v3 and v4. This may suggest that particular functional properties associated with the various GRM7 subtypes could be reflected by their tissue- and/or cell-specific expression.