Metabotropic glutamate receptor 1 splice variants mGluR1a and mGluR1b combine in mGluR1a/b dimers in vivo

The assembly of two covalently linked monomers into dimeric complexes is a prerequisite for metabotropic glutamate receptor 1 (mGluR1) function. The former concept of a strictly homodimeric subunit contribution in metabotropic glutamate receptor complexes has recently been brought into question. Alternative splicing of the GRM1 gene results in expression of variants that vary within their intracellular C-termini. Here we bring evidence that the short mGluR1b variant is found preferentially in a complex with the long mGluR1a variant in the rodent brain. The mGluR1a and mGluR1b variants distribution overlaps in Purkinje cells and the two variants colocalize in their spines. However mGluR1a and mGluR1b show distinct sub-cellular localization when expressed alone in neurons. We discovered that trafficking of mGluR1b to distal dendrites is reliant on its association with mGluR1a and that the long C-terminus of mGluR1a within the mGluR1a/b dimer is necessary for trafficking of the complex.