Revealing Ancestral Arachnid Genes by Tracking Acetylcholinesterase Evolution in Spiders

Abstract

Acetylcholinesterase (AChE) is a vital enzyme which plays a key role in regulation of neurotransmission in spiders and other animals. Because it is of critical importance, this protein is targeted by many toxins, including naturally occurring toxins and man-made pesticides. Due to the evolutionary pressures to circumvent the toxins found in their environment, the AChE genes (ace) of spiders have evolved over time. However, the phylogenetics of ace in spiders have not been extensively documented and have only been examined in detail in a single species, Pardosa pseudoannulata. Studying the evolutionary history of ace genes in spiders can help to determine how the respective roles and the importance of the different spider AChE proteins encoded by these genes have evolved over millions of years. Spiders are abundant predators which are important in controlling terrestrial arthropod populations worldwide, but they are under threat of being poisoned by the application of pesticides. Therefore, investigating the evolution of the various types of AChEs in spiders is also important for understanding the potential impact of pesticides on spiders. To address this knowledge gap, the relationships between previously published AChE amino acid sequences from 15 species of spiders were analyzed in this study. These analyses revealed a diverse array of AChE protein homologs and showed that multiple distinct ace genes often coexist in a single spider genome. Of note, a form of AChE with an amino acid sequence which is evolutionarily conserved even among distantly related spiders was also identified in this study. Since proteins with conserved sequences tend to be highly expressed, this finding suggests that this form of AChE is expressed at a greater level than are other spider AChE proteins. This conserved spider AChE amino acid sequence is similar to AChE sequences not only from other arachnids, but also to those from animals as distantly related as insects, nematodes, and vertebrates. This study has also identified a separate clade of AChE with a less-conserved amino acid sequence, found only in spiders and in other arachnids. To my knowledge, this is the first evolutionary study of AChE across spider lineages, and these results should provide a basis for further research to facilitate protection of these indispensable species.