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γ-Aminobutyric acidA receptor; Splicing; Cerebellum; Recombinant receptors; In situ hybridization
Abstract:
Sequence variation was found in cDNA coding for the extracellular domain of the rat γ-aminobutyric acid type A (GABAA) receptor α6 subunit. About 20% of polymerase chain reaction (PCR)-amplified α6 cDNA prepared from rat cerebellar mRNA lacked nucleotides 226–255 as estimated by counting single-stranded phage plaques hybridized specifically to the short (α6S) and long (wild-type) forms of the α6 mRNA. Genomic PCR revealed an intron located upstream of the 30-nucleotide sequence. Both splice forms were detected in the cerebellum by in situ hybridization. Recombinant receptors, resulting from coexpression of the α6S subunit with the GABAA receptor β2 and γ2 subunits in human embryonic kidney 293 cells, were inactive at binding [3H]muscimol and [3H]Ro 15-4513. In agreement, injection of complementary RNAs encoding the same subunits into Xenopus oocytes produced only weak GABA-induced currents, indistinguishable from those produced by β2γ2 receptors. Therefore, the 10 amino acids encoded by the 30-nucleotide fragment may be essential for the correct assembly or folding of the α6 subunit-containing receptors.
