NEURONALLY RESTRICTED RNA SPLICING REGULATES THE EXPRESSION OF A NOVEL GABA(A) RECEPTOR SUBUNIT CONFERRING ATYPICAL FUNCTIONAL-PROPERTIES

We report the isolation and characterization of a cDNA encoding a nove l member of the GABA receptor gene family, epsilon. This polypeptide i s 506 amino acids in length and exhibits its greatest amino acid seque nce identity with the GABA(A) receptor gamma 3 subunit (47%), although this degree of homology is not sufficient for it to be classified as a fourth gamma subunit. The epsilon subunit coassembles with GABA(A) r eceptor alpha and beta subunits in Xenopus laevis oocytes and transfec ted mammalian cells to form functional GABA-gated channels. alpha 1 be ta 1 epsilon GABA(A) receptors, like alpha 1 beta 1 gamma 2s receptors , are modulated by pentobarbital and the steroid 5 alpha-pregnan-3 alp ha-ol-20-one but, unlike alpha 1 beta 1 gamma 2s receptors, are insens itive to flunitrazepam. Additionally, alpha 1 beta 1 epsilon receptors exhibit rapid desensitization kinetics, as compared with alpha 1 beta 1 or alpha 1 beta 1 gamma 2s. Northern analysis demonstrates widespre ad expression of a large epsilon subunit transcript in a variety of no nneuronal 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 epsilon s ubunit via neuronally restricted RNA splicing. In situ hybridization a nd immunocytochemistry reveal a pattern of expression in the brain res tricted primarily to the hypothalamus, suggesting a role in neuroendoc rine regulation, and also to subfields of the hippocampus, suggesting a role in the modulation of long term potentiation and memory.