RIM3γ is a postsynaptic protein in the rat central nervous system

RIMs (Rab3-interacting molecules) are synaptic proteins essential for neural transmission and plasticity. RIM1 alpha has been implicated in membrane trafficking and regulation of secretory vesicle exocytosis in eukaryotic cells. Little information is as yet available on RIM3 gamma. In the present study, we investigated the cellular expression, subcellular distribution, and possible functions of RIM3 gamma in the rat CNS. Rim3 gamma cDNA was subcloned and the protein expressed in vitro for the generation and purification of a rabbit anti-RIM3 gamma polyclonal antibody. In situ hybridization histochemistry, immunohistochemistry, and immuno-electron microscopy were performed to map expression of the mRNA and protein in the rat CNS. Our results indicated widespread distribution of RIM3 gamma in diverse CNS neuronal cell types. The mRNA was found mainly in the cell bodies, whereas the protein immunoreactivity was localized chiefly to neuronal dendrites and to the postsynaptic densities as visualized under the light and electron microscope. This postsynaptic placement of RIM3 gamma is distinct from the presynaptic localization of RIM1 alpha but may contribute to regulating synaptic transmission and plasticity. The identification of RIM3 gamma as a postsynaptic protein has functional implications for CNS synapse functions.