A role of Rnd1 GTPase in dendritic spine formation in hippocampal neurons.

Rho family of small GTPases are key regulators for morphological changes of neurons on the basis of reorganization of the actin cytoskeleton. Rnd1, a novel member of this family, is predominantly expressed in neurons in brain; however, the neuronal functions of Rnd1 are not known. Here we investigated the effect of Rnd1 on neuronal morphology. Northern blot analysis of Rnd1 expression in rat brain showed that Rnd1 mRNA was highly expressed during early postnatal period, the synaptogenic stage. In situ hybridization analysis at this period revealed that Rnd1 mRNA was strongly expressed in neurons, including the hippocampal pyramidal neurons. Furthermore, immunoblot analysis showed that Rnd1 protein was localized in synaptosomal membrane fraction. Ectopical overexpression of Rnd1 in cultured rat hippocampal neurons promoted the elongation of dendritic spines. On the other hand, suppression of endogenous Rnd1 level by antisense oligonucleotide of Rnd1 caused the increase in the percentage of headless protrusions accompanied by the reduction in the spine number and spine width and shortened the length of the headless protrusions. These results indicate that Rnd1 plays a role in spine formation in the developmental synaptogenic stage.