Abstract
Phenylalanine hydroxylase (PAH) is a crucial enzyme involved in tyrosine biosynthesis, having roles in neurological and physiological processes. The purpose of PAH has received little attention in crustaceans despite extensive investigations in other arthropods. Here, we characterize the PAH gene for the first time in the parasite Lepeophtheirus salmonis, a copepod that is responsible for huge economic losses in salmonid fish farming. Phylogenetic and sequence analyses confirmed that LsPAH is closely related to the metazoan PAH with conserved ACT regulatory and catalytic domains. Temporal expression patterns revealed that LsPAH is expressed throughout all developmental stages peaking during the copepodite stages, suggesting an essential role in developmental physiology. We used RNAi to knockdown LsPAH expression in the nauplius I stage to study developmental function during the larval stages. PAH knockdown impaired larval development, molting and swimming ability with severe morphological defects. This study provides insight into the role of PAH in copepods and demonstrates the importance of this metabolic gene in salmon louse growth and development.
Highlights
The marine ectoparasite of Atlantic salmon (Salmo salar), the salmon louse (Lepeophtheirus salmonis), causes substantial economic loss in salmon aquaculture and represents a significant threat to wild fish populations in both the North Pacific and North Atlantic (Pike, 1989; Torrissen et al, 2013)
We report the effect of downregulating the single copy gene LsPAH that is responsible for phenylalanine hydroxylase activity in salmon lice
We demonstrate a direct effect of LsPAH knockdown on the molting and development of the salmon lice
Summary
The marine ectoparasite of Atlantic salmon (Salmo salar), the salmon louse (Lepeophtheirus salmonis), causes substantial economic loss in salmon aquaculture and represents a significant threat to wild fish populations in both the North Pacific and North Atlantic (Pike, 1989; Torrissen et al, 2013). There are multiple chemical treatments for the louse control in aquaculture, but the majority of these methods are losing their effect due to resistant lice (Aaen et al, 2015). The physiology of lice comprises several important biological systems that are governed by various genes and proteins. Various treatment methods target these genes and proteins necessary in different biological processes such as neuromodulation, body formation, molting, embryonic development, and more. Finding ways to inhibit development and molting could help decrease the lice infestation in farmed fish. Identifying key genes involved in the growth, development, and molting of lice could be the additional step to aid the ongoing research to overcome this problem
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