Characterization of G-protein βγ expression in the inner ear

Heterotrimeric guanine nucleotide binding proteins (G-proteins) are composed of a diverse set of alpha, beta, and gamma subunits, which couple cell surface receptors to intracellular effecters, such as adenylyl cyclase, phospholipase C beta, and ion channels. Both the G alpha and the G beta gamma dimers mediate effector activity and are believed to contribute to the complexity of the signaling pathway. Molecular and immunocytochemical techniques were employed to determine diversity of G beta and G gamma subunit expression in the murine inner ear. PCR-based assessment of lambda ZAP unidirectional cDNA Libraries, representing the cochlea and inner ear hair cells, indicated 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 gamma 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 exhibited restricted expression to inner and outer hair cells, respectively. Antisera 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 cells along the cochlear axis. Collectively, our results demonstrate a complementary as well as differential distribution pattern for G beta and G gamma isoforms exists in the inner ear. The co-localization of various G-protein isoforms within the same cell type suggests specific combinatorial G beta and G gamma subunit associations may preferentially be formed. Thus, the detection of multiple subunits presumably reflects the extent of the functional diversity of inner ear signaling pathways and should provide specificity of G-protein mediated pathways. (C) 1999 Elsevier Science B.V. All rights reserved.