Interaction of nectin-2α with the auxiliary protein of the voltage-gated A-type K + channel Kv4.2 dipeptidyl aminopeptidase-like protein at the boundary between the adjacent somata of clustered cholinergic neurons in the medial habenula.

The medial habenula (MHb) receives septal inputs and sends efferents to the interpeduncular nucleus and is implicated in stress, depression, memory, and nicotine withdrawal syndrome. We previously showed by immunofluorescence microscopy that the cell adhesion molecule nectin-2α is expressed in the cholinergic neurons in the developing and adult mouse MHbs and localized at the boundary between the adjacent somata of clustered cholinergic neurons where the voltage-gated A-type K+ channel Kv4.2 is localized. We further showed by immunoelectron microscopy that Kv4.2 is localized at the membrane specializations (MSs) whereas nectin-2α is localized mostly outside of these MSs. In addition, we showed that genetic ablation of nectin-2 delays the localization of Kv4.2 at the MSs in the developing MHb. We investigated here how nectin-2α regulates this localization of Kv4.2 at the MSs. In vitro biochemical analysis revealed that nectin-2α interacted with the auxiliary protein of Kv4.2 dipeptidyl aminopeptidase-like protein 6 (DPP6), but not with Kv4.2 or another auxiliary protein Kv channel-interacting protein 1 (KChIP1). Immunofluorescence microscopy analysis showed that DPP6 was colocalized with nectin-2α at the boundary between the adjacent somata of the clustered cholinergic neurons in the developing and adult MHbs. Immunoelectron microscopy analysis on this boundary revealed that DPP6 was localized both at the inside and the outside of the MSs. Genetic ablation of nectin-2 did not affect the localization of DPP6 at the boundary between the adjacent somata of the clustered cholinergic neurons in the developing and adult MHbs. These results indicate that nectin-2α interacts with DPP6 but regulates the localization of Kv4.2 at the MSs in a DPP6-independent manner.