The middle M2 (the linker region) and M4 (Linker-PDZ3-PDZ4) fragments were specifically localized to the BC-PC or BC-BC apical surfaces and colocalized with Arm (S10N and S10P Fig), suggesting that the linker region contributes to the specific localization of Dlg5 in BC-PC surfaces where Dlg5 partially colocalized with Arm. This evidence concerns the gene DLG5 and pachyonychia congenita.