Characterization of G-protein beta gamma expression in the inner ear

Heterotrimeric guanine nucleotide binding proteins (G-proteins) are compose d of a diverse set of alpha, beta, and gamma subunits, which couple cell su rface receptors to intracellular effecters, such as adenylyl cyclase, phosp holipase C beta, and ion channels. Both the G alpha and the G beta gamma di mers mediate effector activity and are believed to contribute to the comple xity of the signaling pathway. Molecular and immunocytochemical techniques were employed to determine diversity of G beta and G gamma subunit expressi on in the murine inner ear. PCR-based assessment of lambda ZAP unidirection al cDNA Libraries, representing the cochlea and inner ear hair cells, indic ated all five known G beta subunits were present in the cochlea, while only a subset of G gamma isoforms were found. New or novel G-protein beta and g amma subunits were not detected, cDNAs representing G beta 1-4 and G gamma 2, G gamma 3, G gamma 5, G gamma 8,If subunit transcripts were isolated. In addition, cDNAs corresponding to the G beta 5 and G gamma 11 isoforms exhi bited restricted expression to inner and outer hair cells, respectively. An tisera specific for G beta 3, G beta 4, G gamma 3, G gamma 5 and G gamma 11 stained spiral ganglion and neurosensory hair cells. A unique finding was the variable topological distribution of G gamma 3 in the spiral ganglion c ells along the cochlear axis. Collectively, our results demonstrate a compl ementary as well as differential distribution pattern for G beta and G gamm a isoforms exists in the inner ear. The co-localization of various G-protei n isoforms within the same cell type suggests specific combinatorial G beta and G gamma subunit associations may preferentially be formed. Thus, the d etection of multiple subunits presumably reflects the extent of the functio nal diversity of inner ear signaling pathways and should provide specificit y of G-protein mediated pathways. (C) 1999 Elsevier Science B.V. All rights reserved.