Cellular localization of a variant RAPGEF5 protein associated with idiopathic epilepsy risk in the Belgian shepherd

The Wnt signaling pathway is critical for normal embryonic development. Disruptions in the Wnt signaling pathway have been linked to neurological disorders. The RAPGEF5 protein is a partner in Wnt signaling and a RAPGEF5 3-bp insertion is associated with increased risk for idiopathic epilepsy in the Belgian shepherd dog. The 3-bp insertion risk variant introduces an alanine residue predicted to disrupt the protein. Wildtype and the risk variant RAPGEF5 cDNAs were cloned into green fluorescent protein (GFP) expression vectors and transfected into canine kidney cells. The cellular localization of each GFP-labeled RAPGEF5 protein was assessed. Variant RAPGEF5 protein was altered in its localization from that of the wildtype protein and rather than localized to the nucleus and cytoplasm as seen for the wildtype, it was predominantly found in the cytoplasm. Belgian shepherds with the risk variant for RAPGEF5 may have altered Wnt signaling due to modified intracellular localization which in turn could thereby contribute to the expression of idiopathic epilepsy.