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

This study investigated the effect of single Gαo1 and Gαo2, as well as double Gαo1/2 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 Gαo subunits to the anatomy and synapse formation of the cerebellum. Knockout of Gαo1 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 Gαo2 increased cerebellar size, molecular layer thickness in central lobule II (+18.6%), and area of the culmen (+37%). Combined deletion of Gαo1 and Gαo2 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 Gαo1 knockout mice (on average by 40%). Similarly, VGLUT1 expression was reduced (on average by 17.3%). The knockout of Gαo2 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 Gαo1 and double knockout (-25% and -31% overall number, respectively) and increased for Gαo2 knockout (+13% on average). In line with this, negative effects on the dendritic outgrowth of Purkinje cells were observed in both Gαo1 -/- and Gαo -/-mice, while knockout of Gαo2 promoted dendrite outgrowth. Taken together, the two Gαo splice variants contrarily contribute to the development of the cerebellum, with Gαo1 representing the dominant subunit.