EERNISSE, D.J.; AMER, A.A.; MCCAMAN, R.E.; ONO, J.K.: Gene duplication in gastropod (Mollusca) nicotinic acetylcholine receptor (nAChR) proteins is associated with neuronal vs. neuromuscular specialization.

One of us (AAA) has recently sequenced the alpha subunits of nicotinic acetylcholine receptor proteins (nAChRs) from the central nervous system (CNS) and buccal muscles (BM) of the gastropod molluscs, Aplysia californica, Helix aspersa, and Lymnaea stagnalis. The CNS and BM copies of these nAChRs appear to be paralagous, but the phylogenetic level of this paralogy was unknown. Previous authors had already argued as early as 1995, before their present discovery, that molluscan muscle nAChRs, if they exist, cannot be homologous with vertebrate neuromuscular nAChRs. This claim is supported by our present phylogenetic analysis of our new sequences with over 160 other ligand-gated ion channel (LGIC) sequences, including available nAChR proteins. Our analysis has also revealed that a monophyletic grouping of all our gastropod sequences is nested within a more general monophyletic grouping of exclusively protostome AChR sequences. However, the only other protostome bilaterian AChR sequences presently available in GenBank are various arthropod and nematode sequences, so additional sampling in other protostomes is needed. The characteristics and implications of the separate evolutionary specializations of neuronal vs. neuromuscular synapse proteins in deuterostome and protostome animals will be emphasized.