The human-specific duplicated α7 gene inhibits the ancestral α7, negatively regulating nicotinic acetylcholine receptor-mediated transmitter release

Carolina Martín-Sánchez,Eva Alés,Santiago Balseiro-Gómez,Gema Atienza,Francisco Arnalich,Anna Bordas,José L Cedillo,María Extremera,Arturo Chávez-Reyes,Carmen Montiel

doi:10.1016/j.jbc.2021.100341

Abstract

Gene duplication generates new functions and traits, enabling evolution. Human-specific duplicated genes in particular are primary sources of innovation during our evolution although they have very few known functions. Here we examine the brain function of one of these genes (CHRFAM7A) and its product (dupα7 subunit). This gene results from a partial duplication of the ancestral CHRNA7 gene encoding the α7 subunit that forms the homopentameric α7 nicotinic acetylcholine receptor (α7-nAChR). The functions of α7-nAChR in the brain are well defined, including the modulation of synaptic transmission and plasticity underlying normal attention, cognition, learning, and memory processes. However, the role of the dupα7 subunit remains unexplored at the neuronal level. Here, we characterize that role by combining immunoblotting, quantitative RT-PCR and FRET techniques with functional assays of α7-nAChR activity using human neuroblastoma SH-SY5Y cell variants with different dupα7 expression levels. Our findings reveal a physical interaction between dupα7 and α7 subunits in fluorescent protein-tagged dupα7/α7 transfected cells that negatively affects normal α7-nAChR activity. Specifically, in both single cells and cell populations, the [Ca2+]i signal and the exocytotic response induced by selective stimulation of α7-nAChR were either significantly inhibited by stable dupα7 overexpression or augmented after silencing dupα7 gene expression with specific siRNAs. These findings identify a new role for the dupα7 subunit as a negative regulator of α7-nAChR-mediated control of exocytotic neurotransmitter release. If this effect is excessive, it would result in an impaired synaptic transmission that could underlie the neurocognitive and neuropsychiatric disorders associated with α7-nAChR dysfunction.

Highlights

The α7 nicotinic acetylcholine receptor (α7-nAChR) is a ligand-gated ion channel expressed in neurons and nonneuronal cells of the human brain where it mostly forms homopentameric receptors composed of five α7 subunits [1, 2]
CHRFAM7A expression has been associated with neurocognitive disorders such as schizophrenia, psychosis, bipolar disorder, autism, and dementia [33,34,35], the functional role of the chimeric gene was long unidentified until we reported that its product, the dupα7 subunit, acted as a
In order to avoid differences in the expression levels of dupα7 mRNA among different SH-SY5Y cultures transiently transfected with the dupα7.pcDNA3.1/Myc-His construct, we stably transfected the cells with this construct, or with its corresponding empty vector pcDNA3.1/Myc-His, as described in the corresponding Methods section

Summary

Introduction

The α7 nicotinic acetylcholine receptor (α7-nAChR) is a ligand-gated ion channel expressed in neurons and nonneuronal cells of the human brain where it mostly forms homopentameric receptors composed of five α7 subunits [1, 2].

Results

Conclusion