The nicotinic acetylcholine receptor gene family of the pufferfish, Fugu rubripes☆

Abstract

Nicotinic acetylcholine receptors (nAChRs) mediate fast cholinergic synaptic transmission at nerve–muscle junctions and in the brain. However, the complete gene family of nAChRs has not so far been reported for any vertebrate organism. We have identified the complete nAChR gene family from the reference genome of the pufferfish, Fugu rubripes. It consists of 16 α and 12 non-α candidate subunits, making it the largest vertebrate nAChR gene family known to date. The gene family includes an unusual set of muscle-like nAChR subunits comprising two α1s, two β1s, one δ, one ε, and one γ. One of the β1 subunits possesses an aspartate residue and N-glycosylation sites hitherto shown to be necessary for δ-subunit function. Potential Fugu orthologs of neuronal nAChR subunits α2–4, α6, and β2–4 have been identified. Interestingly, the Fugu α5 counterpart appears to be a non-α subunit. Fugu possesses an expanded set of α7–9-like subunits and no α10 ortholog has been found. Two new candidate β subtypes, designated β5 and β6, may represent subunits yet to be found in the human genome. The Fugu nAChR gene structures are considerably more diverse than those of higher vertebrates, with evidence of “intron gain” in many cases. We show, using RT-PCR, that the Fugu nAChR subunits are expressed in a variety of tissues.