Alternative splicing of mGlu6 gene generates a truncated glutamate receptor in rat retina.

A novel splice variant of metabotropic glutamate receptor type 6 (mGlu6 receptor) was identified by reverse transcription-polymerase chain reaction amplification and sequence analysis of rat retina cDNA. The new rat receptor isoform (mGlu6b receptor) is characterized by an additional exon of 88 nucleotides containing an inframe stop codon, thus predicting the expression of a truncated protein of 508 amino acids. In situ hybridization reveals mGlu6b receptor mRNA to be predominantly expressed in the outer part of the inner nuclear layer of rat retina, containing ON-bipolar cells. The mGlu6b protein would comprise the extracellular domain of the receptor containing the ligand-binding site, but would lack the transmembrane and intracellular portions, thus possibly acting as a retinal soluble receptor for glutamate.