Identification and characterisation of the ecdysone biosynthetic genes neverland, disembodied and shade in the salmon louse Lepeophtheirus salmonis (Copepoda, Caligidae).

Sussie Dalvin,Tor Einar Horsberg,Heidi Kongshaug,Liv Sandlund,Frank Nilsen,Xinghui Qiu,Rune Male

doi:10.1371/journal.pone.0191995

Abstract

The salmon louse is a marine ectoparasitic copepod on salmonid fishes. Its lifecycle consists of eight developmental stages, each separated by a molt. In crustaceans and insects, molting and reproduction is controlled by circulating steroid hormones such as 20-hydroxyecdysone. Steroid hormones are synthesized from cholesterol through catalytic reactions involving a 7,8-dehydrogenase Neverland and several cytochrome P450 genes collectively called the Halloween genes. In this study, we have isolated and identified orthologs of neverland, disembodied and shade in the salmon louse (Lepeophtheirus salmonis) genome. Tissue-specific expression analysis show that the genes are expressed in intestine and reproductive tissue. In addition, levels of the steroid hormones ecdysone, 20-hydroxyecdysone and ponasterone A were measured during the reproductive stage of adult females and in early life stages.

Highlights

The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod (Copepoda, Caligida) infecting salmonid fishes
To verify the sequences of the selected genes, primers were designed from predicted gene sequences from the L. salmonis genome and 5 ́ and 3 ́RACE were performed
The structure of the enzymes involved in ecdysteroid biosynthesis are highly conserved between insects and crustaceans, the physiological function in marine invertebrates has received little attention

Summary

Introduction

The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod (Copepoda, Caligida) infecting salmonid fishes. The parasite feeds on the mucosa, skin and blood of the host creating open wounds that increase the chance of secondary infections and mortality. The lice cause a serious threat to farming of Atlantic salmon in Norway, UK, USA and Canada and are estimated to contribute to an annual loss of more than 500 million USD in Norway alone http:// nofima.no/nyhet/2015/08/kostnadsdrivere-i-oppdrett/. Adult females produce batches of oocytes that are generated in coiled tubular structures that form the ovaries in the anterior part of the animal and are transported to the genital segment through the oviduct [4]. The eggs mature inside the genital segment where lipids and vitellogenins are incorporated

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