Acetylcholinesterase (AChE, EC 3.1.1.7) plays a vital role in neurotransmission in both vertebrates and invertebrates. AChE is a key enzyme in the insect nervous system, in which the cholinergic system is essential. In addition to its classical synaptic functions, AChE is recently known to play other non-neuronal roles. In vertebrates, only one AChE has been shown to be involved in both neuronal and non-neuronal functions, whereas two different AChEs have been identified from various insect species, and seem to play respective neuronal and non-neuronal functions. In honey bee, for instance, membrane-anchored AChE2 is reported to be responsible for classical synaptic functions, while soluble AChE1 plays non-neuronal functions. In contrast to most insect species expressing two AChEs, Cyclorrhaphan flies are known to possess only a single ace locus. In Cyclorrhapha possessing only one AChE, multiple forms (molecular variation) of Drosophila melanogaster AChE (DmAChE) were recently suggested to be generated via alternative splicing. Among various molecular forms, membrane-anchored dimer has high enzyme activity, whereas soluble monomer is abundantly expressed without catalytic activity. Interestingly, expression of the soluble DmAChE was induced by chemical stress. Based on the results, it can be hypothesized that the generation of multiple isoforms of AChE2, particularly the soluble forms, may have provided alternative protein copies for AChE1, replaced the functions of AChE1 and eventually allowed the loss of AChE1 in Cyclorrhaphan flies.

• Young Ho Kim(Research Institute for Agriculture and Life Sciences, Seoul National University)
• Si Hyeock Lee(Research Institute for Agriculture and Life Sciences, Seoul National University, Department of Agricultural Biotechnology, Seoul National University)