Splice Type-Specific Effects of Gαo Subunits on Cerebellar Anatomy and Synapse Formation

This study investigated the effect of single Gα_o1 and Gα_o2, as well as double Gα_o1/2 knockout on the cerebellar anatomy and synapse formation. The alpha subunit of the G protein Go exists in two splice variants. Knockout of certain Gαo subtypes result in strong-mainly motor-deficits in mice, and mutations in the responsible gene locus in humans can result in severe encephalopathies. We aimed to decipher the hitherto incompletely understood contribution of the individual Gα_o subunits to the anatomy and synapse formation of the cerebellum. Knockout of Gα_o1 reduced the size of the cerebellum by 11%, accompanied by maximal reductions of the molecular layer thickness in the central lobule III (-30%) and molecular layer area in the uvula (-33%). Knockout of Gα_o2 increased cerebellar size, molecular layer thickness in central lobule II (+18.6%), and area of the culmen (+37%). Combined deletion of Gα_o1 and Gα_o2 reduced cerebellar size by 12%, molecular layer thickness and area of the declive (by -27.3% and -23.4%, respectively). Moreover, VGLUT2-positive climbing fiber contacts to Purkinje cells were reduced in Gα_o1 knockout mice (on average by 40%). Similarly, VGLUT1 expression was reduced (on average by 17.3%). The knockout of Gα_o2 promoted climbing fiber contacts (+14.3% on average, at a maximum of +52.6% in the central lobule II), VGLUT1 was less affected. Double knockout mice exhibited negative effects on VGLUT2 (-35% overall number) and VGLUT1 (-23% on average in expression levels). VGAT-positive synaptic contacts were also diminished for Gα_o1 and double knockout (-25% and -31% overall number, respectively) and increased for Gα_o2 knockout (+13% on average). In line with this, negative effects on the dendritic outgrowth of Purkinje cells were observed in both Gα_o1 ^-/- and Gα_o ^-/-mice, while knockout of Gα_o2 promoted dendrite outgrowth. Taken together, the two Gαo splice variants contrarily contribute to the development of the cerebellum, with Gα_o1 representing the dominant subunit.