Functional role of the duplicated α7 nicotinic receptor subunit

LASALA M; DIONISIO, L.; CORRADI J.; CHRESTIA F.; ESANDI, M.C.; BOUZAT, C.

Mar del Plata

Congreso; XXX Reunión Anual de SAN; 2015

SAN

The α7 nicotinic receptor subunit gene, CHRNA7, codes for a subunit that forms the homomeric α7 receptor, which is involved in learning and memory. Exons 5-10 of CHRNA7 were duplicated upstream interrupting another partial duplication of the gene ULK4, called FAM. The product of the resulting chimeric gene (CHRFAM7A), dupα7, is a receptor subunit that lacks part of the ACh binding site. We here combine cell expression and electrophysiological recordings in HEK cells to understand the functional role of the dup7 subunit. Incorporation of dup7 cDNA during cell transfection with 7 cDNA reduces surface -BTX labeling, indicating reduced number of 7 binding sites, and in turn, suggesting a negative modulatory role. To determine if dup7 can assemble into functional receptors we used, as a reporter of receptor stoichiometry, an 7 subunit (7LC) carrying mutations in determinants of ion conductance. 7LC forms functional receptors but single-channel openings cannot be detected due to their low conductance. Co-expression of 7LC with dup7, which by itself does not form functional receptors, allows detection of single-channel openings elicited by ACh. This result unequivocally indicates that α7 and dupα7 subunits assemble into functional heteromeric receptors. The analysis shows that a minimum of two 7 subunits is required for forming functional receptors. Our results contribute to the understanding of the functional significance of the partial duplication of the 7 gene.