Functional role of the duplicated alpha7 nicotinic receptor subunit

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

Mar del Plata

Congreso; XXX Reunión Anual de la Sociedad Argentina de Investigación en Neurociencias (SAN); 2015

Sociedad Argentina de Investigación en Neurociencias (SAN)

The  alpha7 nicotinicreceptor subunit gene, CHRNA7, codes for a subunit that forms the homomeric  alpha7 receptor, whichis involved in learning and memory. Exons 5-10 of CHRNA7 were duplicatedupstream interrupting another partial duplication of the gene ULK4, called FAM.The product of the resulting chimeric gene (CHRFAM7A), dupAlpha7, is a receptorsubunit that lacks part of the ACh binding site. We here combine cellexpression and electrophysiological recordings in HEK cells to understand the functionalrole of the dupAlpha7subunit. Incorporation of dupAlpha7 cDNA during cell transfectionwith  alpha7 cDNA reduces surface a-BTX  labeling, indicating reduced number of  alpha7 binding sites, and inturn, suggesting a negative modulatory role. To determine if dupAlpha7 canassemble into functional receptors we used, as a reporter of receptorstoichiometry, an  alpha7 subunit (alpha7LC) carryingmutations in determinants of ion conductance.  alpha7LC forms functional receptors but single-channelopenings cannot be detected due to their low conductance. Co-expression of  alpha7LC with dupAlpha7,which by itself does not form functional receptors, allows detection of single-channelopenings elicited by ACh. This result unequivocally indicates that  alpha7 and dupAlpha7 subunitsassemble into functional heteromeric receptors. The analysis shows that aminimum of two  alpha7 subunits is required for forming functional receptors.   Our results contribute to the understandingof the functional significance of the partial duplication of the  alpha7 gene.