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

Cerebellar granule cells express six GABAAreceptor subunits abundantly (α1, α6, β2, β3, γ2, 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 α6protein from cerebellar granule cells allowed perturbations in other subunit levels to be studied. Exon 8 of the mouse α6subunit gene was disrupted by homologous recombination. In α6−/− 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 α6and δ subunits. Because in α6−/− neurons the remaining α1, β2/3, and γ2subunits cannot rescue the δ subunit, certain potential subunit combinations may not be found in wild-type cells.