Identification and Molecular Characterization of Two Acetylcholinesterases from the Salmon Louse, <i>Lepeophtheirus salmonis</i>

<div><p>Acetylcholinesterase (AChE) is an important enzyme in cholinergic synapses. Most arthropods have two genes (<i>ace1</i> and <i>ace2</i>), but only one encodes the predominant synaptic AChE, the main target for organophosphates. Resistance towards organophosphates is widespread in the marine arthropod <i>Lepeophtheirus salmonis</i>. To understand this trait, it is essential to characterize the gene(s) coding for AChE(s). The full length cDNA sequences encoding two AChEs in <i>L</i>. <i>salmonis</i> were molecularly characterized in this study. The two ace genes were highly similar (83.5% similarity at protein level). Alignment to the <i>L</i>. <i>salmonis</i> genome revealed that both genes were located close to each other (separated by just 26.4 kbp on the <i>L</i>. <i>salmonis</i> genome), resulting from a recent gene duplication. Both proteins had all the typical features of functional AChE and clustered together with AChE-type 1 proteins in other species, an observation that has not been described in other arthropods. We therefore concluded the presence of two versions of <i>ace1</i> gene in <i>L</i>. <i>salmonis</i>, named <i>ace1a</i> and <i>ace1b</i>. <i>Ace1a</i> was predominantly expressed in different developmental stages compared to <i>ace1b</i> and was possibly active in the cephalothorax, indicating that <i>ace1a</i> is more likely to play the major role in cholinergic synaptic transmission. The study is essential to understand the role of AChEs in resistance against organophosphates in <i>L</i>. <i>salmonis</i>.</p>