The Duplicated α7 Subunits Assemble and Form Functional Nicotinic Receptors with the Full-length α7

The alpha 7 nicotinic acetylcholine receptor gene (CHRNA7) is linked to schizophrenia. A partial duplication of CHRNA7 (CHRFAM7A) is found in humans on 15q13-14. Exon 6 of CHRFAM7 A harbors a 2-bp deletion polymorphism, CHRFAM7A-Delta 2bp, which is also associated with schizophrenia. To understand the effects of the duplicated subunits on alpha 7 receptors, we fused alpha 7, dup alpha 7, and dup Delta alpha 7 subunits with various fluorescent proteins. The duplicated subunits co-localized with full-length alpha 7 subunits in mouse neuroblastoma cells (Neuro2a) as well as rat hippocampal neurons. We investigated the interaction between the duplicated subunits and full-length alpha 7 by measuring Forster resonance energy transfer using donor recovery after photobleaching and fluorescence lifetime imaging microscopy. The results revealed that the duplicated proteins co-assemble with alpha 7. In electrophysiological studies, Leu at the 9'-position in the M2 membrane-spanning segment was replaced with Cys in dup alpha 7 or dup Delta alpha 7, and constructs were co-transfected with full-length alpha 7 in Neuro2a cells. Exposure to ethylammonium methanethiosulfonate inhibited acetylcholine-induced currents, showing that the assembled functional nicotinic acetylcholine receptors (nAChRs) included the duplicated subunit. Incorporation of dup alpha 7 and dup Delta alpha 7 subunits modestly changes the sensitivity of receptors to choline and varenicline. Thus, the duplicated proteins are assembled and transported to the cell membrane together with full-length alpha 7 subunits and alter the function of the nAChRs. The characterization of dup alpha 7 and dup Delta alpha 7 as well as their influence on alpha 7 nAChRs may help explain the pathophysiology of schizophrenia and may suggest therapeutic strategies.