Differential distribution of G-protein β-subunits in brain:: An immunocytochemical analysis

Heterotrimeric G proteins play central roles in signal transduction of neurons and other cells. The variety of their alpha-, beta-, and gamma-subunits allows numerous combinations thereby confering specificity to receptor-G-protein-effector interactions. Using antisera against individual G-protein beta-subunits we here present a regional and subcellular distribution of G beta(1), G beta(2), and G beta(5) in rat brain. Immunocytochemical specificity of the subtype-specific antisera is revealed in Sf9 cells infected with various G-protein beta-subunits. Since G beta-subunits together with a G-protein gamma-subunit affect signal cascades we include a distribution of the neuron-specific G gamma(2)- and G gamma(3)-subunits in selected brain areas, G beta(1), G beta(2), and G beta(5) are preferentially distributed in the neuropil of hippocampus, cerebellum and spinal cord, G beta(2) is highly concentrated in the messy fibres of dentate gyrus neurons ending in the stratum lucidum of hippocampal CA3-area, High amounts of G beta(2) also occur in interneurons innervating spinal cord alpha-motoneurons, G beta(5) is differentially distributed in all brain areas studied. It is found in the pyramidal cells of hippocampal CA1-CA3 as well as in the granule cell layer of dentate gyrus and in some interneurons. In the spinal cord G beta(5); in contrast to G beta(2) concentrates around a-motoneurons, In cultivated mouse hippocampal and hypothalamic neurons G beta(2) and G beta(5) are found in different subcellular compartments. Whereas G beta(5) is restricted to the perikarya, G beta(2) is also found in processes and synaptic contacts where it partially colocalizes with the synaptic vesicle protein sygnaptobrevin. An antiserum recognizing G gamma(2) and G gamma(3) reveals that these subunits are less expressed in hippocampus and cerebellum. Presumably this antiserum specifically recognizes G gamma(2) and G gamma(3) in combinations with certain G alpha s and/or G beta s. The widespread but regionally and cellularly rather different distribution of G beta- and G gamma(2/3)-subunits suggests that region-specific combinations of G-protein subunits mediate signal transduction in the central nervous system. The different subcellular distribution of G beta-subunits in cultivated neurons reflects that observed in tissue where G beta(5) and G beta(2) associate preferentially with the perikarya and the neuropil, respectively, and suggests an additional association of G beta(2) with secretory vesicles.