Neurofascin regulates the formation of gephyrin clusters and their subsequent translocation to the axon hillock of hippocampal neurons

Little is known about the role of cell adhesion molecules (CAMs) in inhibitory synapse development. In particular, a functional link between CAMs and the clustering of postsynaptic scaffold component gephyrin, which is a critical determinant of γ-aminobutyric acid A (GABA) receptor clustering, still needs to be elaborated. At early stages of inhibitory synapse formation, gephyrin and CAM neurofascin are diffusely expressed in the soma of hippocampal neurons. Subsequently, gephyrin clusters become localized to the axon hillock and neurofascin is observed all over the soma including the axon hillock suggesting a function for neurofascin in gephyrin clustering. Transfection of expression vectors for different isoforms and mutants of neurofascin revealed that neurofascin is required for the formation of gephyrin clusters presumably dependent on extracellular interactions. Furthermore, expression of neurofascin is necessary for the translocation of gephyrin clusters to the axon hillock of hippocampal neurons as shown by shRNA-mediated knockdown. In addition, overexpression of an embryonic neurofascin isoform is sufficient for functional rescue after knockdown of endogenous neurofascin.