RIMs (Rab3-interacting molecules) are synaptic proteins essential for neural transmission and plasticity. RIM1alpha has been implicated in membrane trafficking and regulation of secretory vesicle exocytosis in eukaryotic cells. Little information is as yet available on RIM3gamma. In the present study, we investigated the cellular expression, subcellular distribution, and possible functions of RIM3gamma in the rat CNS. Rim3gamma cDNA was subcloned and the protein expressed in vitro for the generation and purification of a rabbit anti-RIM3gamma polyclonal antibody. In situ hybridization histochemistry, immunohistochemistry, and immunoelectron microscopy were performed to map expression of the mRNA and protein in the rat CNS. Our results indicated widespread distribution of RIM3gamma 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 RIM3gamma is distinct from the presynaptic localization of RIM1alpha but may contribute to regulating synaptic transmission and plasticity. The identification of RIM3gamma as a postsynaptic protein has functional implications for CNS synapse functions.
(c) 2007 Wiley-Liss, Inc.