Phospholipase Cβ3 is distributed in both somatodendritic and axonal compartments and localized around perisynapse and smooth endoplasmic reticulum in mouse Purkinje cell subsets

Phospholipase C beta 3 (PLC beta 3) and PLC beta 4 are the two major isoforms in cerebellar Purkinje cells (PCs), displaying reciprocal expression across the cerebellum. Here, we examined subcellular distribution of PLC beta 3 in the mouse cerebellum by producing specific antibody. PLC beta 3 was detected as a particulate pattern of immunostaining in various PC elements. Like PLC beta 4, PLC beta 3 was richly distributed in somatodendritic compartments, where it was colocalized with molecules constituting the metabotropic glutamate receptor (mGluR1) signalling pathway, i.e. mGluR1 alpha, G alpha q/G alpha 11 subunits of Gq protein, inositol 1,4,5-trisphosphate receptor IP3R1, Homer1, protein kinase C PKC gamma, and diacylglycerol lipase DAGL alpha. Unlike PLC beta 4, PLC beta 3 was also distributed at low to moderate levels in PC axons, which were intense for IP3R1 and PKC gamma, low for G alpha q/G alpha 11, and negative for mGluR1 alpha, Homer1, and DAGL alpha. By immunoelectron microscopy, PLC beta 3 was preferentially localized around the smooth endoplasmic reticulum in spines, dendrites, and axons of PCs, and also accumulated at the perisynapse of parallel fibre-PC synapses. Consistent with the ultrastructural localization, PLC beta 3 was biochemically enriched in the microsomal and postsynaptic density fractions. These results suggest that PLC beta 3 plays a major role in mediating mGluR1-dependent synaptic transmission, plasticity, and integration in PLC beta 3-dominant PCs, through eliciting Ca2+ release, protein phosphorylation, and endocannabinoid production at local somatodendritic compartments. Because PLC beta 3 can be activated by G beta gamma subunits liberated from Gi/o and Gs proteins as well, axonal PLC beta 3 seems to modulate the conduction of action potentials through mediating local Ca2+ release and protein phosphorylation upon activation of a variety of G protein-coupled receptors other than mGluR1.