Characterization of G-protein βγ expression in the inner ear

Heterotrimeric guanine nucleotide binding proteins (G-proteins) are composed of a diverse set of α, β, and γ subunits, which couple cell surface receptors to intracellular effectors, such as adenylyl cyclase, phospholipase Cβ, and ion channels. Both the Gα and the Gβγ 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 Gβ and Gγ subunit expression in the murine inner ear. PCR-based assessment of λZAP unidirectional cDNA libraries, representing the cochlea and inner ear hair cells, indicated all five known Gβ subunits were present in the cochlea, while only a subset of Gγ isoforms were found. New or novel G-protein β and γ subunits were not detected, cDNAs representing Gβ1-4 and Gγ2, Gγ3, Gγ5, Gγ8(olf) subunit transcripts were isolated. In addition, cDNAs corresponding to the Gβ5 and Gγ11 isoforms exhibited restricted expression to inner and outer hair cells, respectively. Antisera specific for Gβ3, Gβ4, Gγ3, Gγ5 and Gγ11 stained spiral ganglion and neurosensory hair cells. A unique finding was the variable topological distribution of Gγ3 in the spiral ganglion cells along the cochlear axis. Collectively, our results demonstrate a complementary as well as differential distribution pattern for Gβ and Gγ isoforms exists in the inner ear. The co-localization of various G-protein isoforms within the same cell type suggests specific combinatorial Gβ and Gγ 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.