IN-SITU HYBRIDIZATION LOCALIZATION OF THE GABA(A) RECEPTOR BETA-2S-SUBUNIT AND BETA-2L-SUBUNIT TRANSCRIPTS REVEALS CELL-SPECIFIC SPLICING OF ALTERNATE CASSETTE EXONS

We have recently described two variants of the chicken GABA(A) recepto r beta 2 subunit which arise by alternative splicing of the correspond ing primary gene transcript. The long form of the beta 2 subunit (beta 2L) differs From the short form (beta 2S) by the insertion of an addi tional 17 amino acids, in the large presumed intracellular loop, betwe en the third and fourth membrane-spanning domains. In this study, we h ave utilized in situ hybridization with transcript-specific oligonucle otide probes to determine the regional and cellular localizations of t he beta 2S- and beta 2L-subunit messenger RNAs in the one-day-old chic k brain. We show that the beta 2-subunit gene is expressed in many bra in areas that also transcribe the GABA(A) receptor alpha 1- and gamma 2-polypeptide genes. We also demonstrate that while the beta 2S- and b eta 2L-subunit messenger RNAs frequently co-localize in many brain are as, certain structures (e.g., the ectostriatum, the hippocampus, the n ucleus solitarius, the nucleus isthmi, pars parvocellularis, the nucle us isthmi, pars magnocellularis, the paleostriatum primitivum, the Pur kinje cell layer, and the deep cerebellar nuclei) exclusively or predo minantly contain either the beta 2S- or the beta 2L-subunit transcript . The distributions of the beta 2S- and beta 2L-polypeptide messenger RNAs resemble those previously described for the chicken GABA(A) recep tor gamma 2S- and gamma 2L-subunit transcripts, respectively, which ar e also generated by alternative splicing. Our results indicate that a major GABA(A) receptor subtype in the avian brain is comprised of alph a 1, beta 2 and gamma 2 subunits. In addition, the data obtained revea l that many neurons in the chicken CNS are capable of producing more t han one alternatively spliced form of a given primary gene transcript. However, the avian brain also appears to contain two small population s of neurons that possess mechanisms that result in either the incorpo ration of alternate cassette exons into mature transcripts, or the exc lusion of such exons from processed messenger RNAs. (C) 1997 IBRO.