Acetylcholine is the major excitatory
neurotransmitter controlling motor activities in nematodes, and the
enzyme which hydrolyses and inactivates
acetylcholine,
acetylcholinesterase, is thus essential for regulation of
cholinergic transmission. Different forms of
acetylcholinesterase are encoded by multiple genes in nematodes, and analysis of the pattern of expression of these genes in Caenorhabditis elegans suggests that they perform non-redundant functions. In addition, many parasitic species which colonise host mucosal surfaces secrete hydrophilic variants of
acetylcholinesterase, although the function of these
enzymes is still unclear. Acetylcholinesterases have a history as targets for therapeutic agents against helminth parasites, but
anti-cholinesterases have been used much more extensively as pesticides, for example to control crop damage and
ectoparasitic infestation of livestock. The toxicity associated with these compounds (generally
organophosphates and
carbamates) has led to legislation to withdraw them from the market or restrict their use in many countries. Nevertheless, acetylcholinesterases provide a good example of a neuromuscular target
enzyme in helminth parasites, and it may yet be possible to develop more selective inhibitors. In this article, we describe what is known about the structure and function of vertebrate
cholinesterases, illustrate the molecular diversity and tissue distribution of these
enzymes in C. elegans, and discuss to what extent this may represent a paradigm for nematodes in general.