KCC2 interacts with gephyrin via its C-terminal domain. A, Immunoblot of coimmunoprecipitation samples prepared from adult rat cortex. Solubilized membrane homogenates (input) were immunoprecipitated with antibodies raised against gephyrin (Gphn), KCC2 or with control IgG. Input and immunoprecipitated proteins were probed with both KCC2 (top) and gephyrin (bottom) antibodies. B, Immunoblots of immunoprecipitates from Neuro2a cell homogenates coexpressing either Flag-tagged full-length KCC2 (KCC2-FL, left) or KCC2-CTD (right) and either GFP-tagged gephyrin (Gphn-GFP) or GFP. Input and immunoprecipitated proteins were probed with both KCC2 (top) and GFP (bottom) antibodies. Immunoprecipitation with GFP antibody pulled down full-length KCC2 and KCC2-CTD in cells expressing Gphn-GFP but not GFP only. Representative blots from four and three independent experiments are shown in A and B, respectively.