Neuronally restricted RNA splicing regulates the expression of a novel GABA(A) receptor subunit conferring atypical functional properties

Abstract

We report the isolation and characterization of a cDNA encoding a novel member of the GABA receptor gene family, ε. This polypeptide is 506 amino acids in length and exhibits its greatest amino acid sequence identity with the GABA(A) receptor γ3 subunit (47%), although this degree of homology is not sufficient for it to be classified as a fourth γ subunit. The ε subunit coassembles with GABA(A) receptor α and β subunits in Xenopus laevis oocytes and transfected mammalian cells to form functional GABA-gated channels. α1β1ε GABA(A) receptors, like α1β1γ2s receptors, are modulated by pentobarbital and the steroid 5α-pregnan-3α-ol-20-one but, unlike α1β1γ2s receptors, are insensitive to flunitrazepam. Additionally, α1β1 ε receptors exhibit rapid desensitization kinetics, as compared with α1β1 or α1β1γ2s. Northern analysis demonstrates widespread expression of a large ε subunit transcript in a variety of non-neuronal tissues and expression of a smaller transcript in brain and spinal cord. Sequence analysis demonstrated that the large transcript contained an unspliced intron, whereas the small transcript represents the mature mRNA, suggesting regulation of expression of the ε subunit via neuronally restricted RNA splicing. In situ hybridization and immunocytochemistry reveal a pattern of expression in the brain restricted primarily to the hypothalamus, suggesting a role in neuroendocrine regulation, and also to subfields of the hippocampus, suggesting a role in the modulation of long term potentiation and memory.