Abstract
The Salmon louse (Lepeophtheirus salmonis) is a marine ectoparasite of salmonid fish in the Northern Hemisphere and considered as a major challenge in aquaculture and a threat to wild populations of salmonids. Adult female lice produce a large number of lipid-rich eggs, however, the mechanism of maternal lipid transport into developing eggs during salmon louse reproduction has not been described. In the present study, a full-length L. salmonis lipophorin receptor (LsLpR) consisting of 16 exons was obtained by RACE and RT-PCR. The predicted ORF was 952 amino acids and structural analysis showed five functional domains that are similar to LpR of insects and decapods. Phylogenetic analysis placed the LsLpR together with LpRs from decapods and insects. Expression analysis revealed that the relative abundance of LsLpR transcripts was highest in the larvae and adult female lice. In adult females, the LsLpR transcripts and protein were found in the ovary and vitellogenic oocytes whereas, in larvae, the LsLpR transcripts were found in the neuronal somata of the brain and the intestine. Oil Red O stain results revealed that storage of neutral lipids was found in vitellogenic oocytes and ovaries of adult females, and in the yolk of larvae. Moreover, RNA interference (RNAi) was conducted to demonstrate the function of LsLpR in reproduction and lipid metabolism in L. salmonis. In larvae, the transcription of LsLpR was decreased by 44–54% while in an experiment LsLpR knockdown female lice produced 72% less offspring than control lice.
Highlights
A full-length cDNA encoding L. salmonis lipophorin receptor (LsLpR) was isolated from adult females of L. salmonis
The open reading frame (ORF) of LsLpR encodes a putative protein consisting of 952 amino acids, with the signal peptide at position 1–23, the predicted molecular weight (Mw) of 107.04 kDa and the theoretical isoelectric point of 4.81
A BLAST search against the UniProtKB/Swiss-Prot revealed that lipophorin receptor (LpR) of L. salmonis shared 46% identity (70.8% similarity) with the Lipoprotein receptor 1 from the crustacean Pandalopsis japonica and ~48–53% identity (~74–77% similarity) with insect LpRs such as Locusta migratoria, Aedes aegypti, Galleria mellonella, Bombyx mori, Blattella germanica (German cockroach) and Drosophila melanogaster
Summary
The salmon louse (Lepeophtheirus salmonis) is a marine ectoparasitic copepod that infests salmonids in Norway, Scotland, Ireland and Canada. It feeds on blood, mucus and skin of hosts in sea water, which leads to major health and welfare issues of fish and results in a major economic losses in the Atlantic salmon (Salmo Salar) farming industry [1]. The salmon louse has been considered to be a threat to wild salmonids [2]. The life cycle of the salmon louse comprises of eight developmental stages, each stage separated by a moult [3].
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