DEG-3 is a subunit of a nicotinic acetylcholine receptor (nAChR) that can mutate to cause neuronal degeneration. The degeneration causing mutation
deg-3(
u662) affects a residues in the pore lining domain of the receptor and is thought to cause degeneration by its effect on channel gating. To further understand how a single missense mutation leads to such a dramatic effect we are using electrophysiological analysis of the normal and mutant DEG-3 channel in an accessible heterologus expression system, Xenopus oocytes. DEG-3 channel activity is seen when co-expressed with
des-2 , also a nAChR subunit. This gene was originally identified as a supressor of
deg-3(
u662) . It is also part of the
deg-3 operon, and is therfore likely to be a subunit of the DEG-3 receptor in-vivo. The DEG-3/DES-2 reconstruction of DEG-3 channel activity shows that indeed the
u662 mutation affects channel gating, including a defect in channel desensitization. However, such a defect does not provide an explanation to DEG-3(
u662 ) induced degenerations as the limiting factor for ACh gated channel activity is the elimination of ACh by acetylcholinesterases, and not receptor desensitization. Electrophysiological analysis also revealed that choline, a metabolite that is constitutively present in most organisms, is an agonist of the DEG-3 receptor. This finding suggested that low constitutive levels of choline, when combined with the
u662 mutation, may lead to
deg-3 dependent degenerations. Indeed oocytes expressing
deg-3(
u662) and not
deg-3 die when incubated with physiological concentrations of choline. Thus the heterolgous expression of DEG-3(
u662 ) and DES-2 allows reconstruction of the cytotoxic processes induced by
deg-3(
u662) . Additional details of the analysis of the DEG-3 channel will be presented.