Rescue of γ2 subunit-deficient mice by transgenic overexpression of the GABA(A) receptor γ2S or γ2L subunit isoforms

The γ2 subunit is an important functional determinant of GABA(A) receptors and is essential for formation of high-affinity benzodiazepine binding sites and for synaptic clustering of major GABA(A) receptor subtypes along with gephyrin. There are two splice variants of the γ2 subunit, γ2 short (γ2S) and γ2 long (γ2L), the latter carrying in the cytoplasmic domain an additional eight amino acids with a putative phosphorylation site. Here, we show that transgenic mice expressing either the γ2S or γ2L subunit on a γ2 subunit-deficient background are phenotypically indistinguishable from wild-type. They express nearly normal levels of γ2 subunit protein and [³H]flumazenil binding sites. Likewise, the distribution, number and size of GABA(A) receptor clusters colocalized with gephyrin are similar to wild-type in both juvenile and adult mice. Our results indicate that the two γ2 subunit splice variants can substitute for each other and fulfil the basic functions of GABA(A) receptors, allowing in vivo studies that address isoform-specific roles in phosphorylation-dependent regulatory mechanisms.