Roles of afadin in the formation of the cellular architecture of the mouse hippocampus and dentate gyrus.

The hippocampal formation with tightly packed neurons, mainly at the dentate gyrus, CA3, CA2, and CA1 regions, constitutes a one-way neural circuit, which is associated with learning and memory. We previously showed that the cell adhesion molecules nectins and its binding protein afadin play roles in the formation of the mossy fiber synapses which are formed between the mossy fibers of the dentate gyrus granule cells and the dendrites of the CA3 pyramidal cells. We showed here that in the afadin-deficient hippocampal formation, the dentate gyrus granules cells and the CA3, CA2, and CA1 pyramidal cells were abnormally located; the mossy fiber trajectory was abnormally elongated; the CA3 pyramidal cells were abnormally differentiated; and the densities of the presynaptic boutons on the mossy fibers and the apical dendrites of the CA3 pyramidal cells were decreased. These results indicate that afadin plays roles not only in the formation of the mossy fiber synapses but also in the formation of the cellular architecture of the hippocampus and the dentate gyrus.