Genetics, Vol. 160, 1519-1533, April 2002, Copyright © 2002

Novel Putative Nicotinic Acetylcholine Receptor Subunit Genes, D{alpha}5, D{alpha}6 and D{alpha}7, in Drosophila melanogaster Identify a New and Highly Conserved Target of Adenosine Deaminase Acting on RNA-Mediated A-to-I Pre-mRNA Editing

M. Grausoa, R. A. Reenanb, E. Culettoa, and D. B. Sattellea
a MRC Functional Genetics Unit, Department of Human Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, United Kingdom
b Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, Connecticut 06030

Corresponding author: D. B. Sattelle, Department of Human Anatomy and Genetics, University of Oxford, S. Parks Rd., Oxford OX1 3QX, United Kingdom., david.sattelle{at}anat.ox.ac.uk (E-mail)

Communicating editor: A. J. LOPEZ

Genome analysis of the fruit fly Drosophila melanogaster reveals three new ligand-gated ion channel subunits with the characteristic YXCC motif found only in {alpha}-type nicotinic acetylcholine receptor subunits. The subunits are designated D{alpha}5, D{alpha}6, and D{alpha}7. Cloning of the D{alpha}5 embryonic cDNAs reveals an atypically large N terminus, part of which is without identifiable sequence motifs and is specified by two polymorphic alleles. Embryonic clones from D{alpha}6 contain multiple variant transcripts arising from alternative splicing as well as A-to-I pre-mRNA editing. Alternative splicing in D{alpha}6 involves exons encoding nAChR functional domains. The D{alpha}6 transcript is a target of the Drosophila adenosine deaminase acting on RNA (dADAR). This is the first case for any organism where a nAChR gene is the target of mRNA editing. Seven adenosines could be modified in the extracellular ligand-binding region of D{alpha}6, four of which are also edited in the D{alpha}6 ortholog in the tobacco budworm Heliothis virescens. The conservation of an editing site between the insect orders Diptera and Lepidoptera makes nAChR editing the most evolutionarily conserved invertebrate RNA editing site so far described. These findings add to our understanding of nAChR subunit diversity, which is increased and regulated by mechanisms acting at the genomic and mRNA levels.