Ligand-Gated Ion Channel Subunit Partnerships: GABA_AReceptor α₆Subunit Gene Inactivation Inhibits δ Subunit Expression

Abstract

Cerebellar granule cells express six GABA A receptor subunits abundantly (α 1 , α 6 , β 2 , β 3 , γ 2 , and δ) and assemble various pentameric receptor subtypes with unknown subunit compositions; however, the rules guiding receptor subunit assembly are unclear. Here, removal of intact α 6 protein from cerebellar granule cells allowed perturbations in other subunit levels to be studied. Exon 8 of the mouse α 6 subunit gene was disrupted by homologous recombination. In α 6 −/− granule cells, the δ subunit was selectively degraded as seen by immunoprecipitation, immunocytochemistry, and immunoblot analysis with δ subunit-specific antibodies. The δ subunit mRNA was present at wild-type levels in the mutant granule cells, indicating a post-translational loss of the δ subunit. These results provide genetic evidence for a specific association between the α 6 and δ subunits. Because in α 6 −/− neurons the remaining α 1 , β 2/3 , and γ 2 subunits cannot rescue the δ subunit, certain potential subunit combinations may not be found in wild-type cells.