Characterisation of two vitellogenins in the salmon louse Lepeophtheirus salmonis: molecular, functional and evolutional analysis

The salmon louse Lepeophtheirus salmonis Kroyer affects a variety of wild salmonoid hosts, but is also an important pest in aquaculture, which is a globally important and rapidly growing industry. Salmon lice have large reproductive outputs, and knowledge of reproductive processes may be crucial for the control of this parasite. Here, we report on the characterisation of 2 vitellogenins (LsVit1 and LsVit2), which are the precursors of salmon-louse egg-yolk glycoprotein. The structure of LsVit1 and LsVit2 was examined and compared to that in other oviparous animals. Phylogenetic analysis of LsVit1 and LsVit2 confirmed the view that crustaceans are a polyphyletic group. Transcriptional and translational analysis demonstrated production of LsVit1 and LsVit2 in the subcuticular tissue of the adult female lice. LsVit1 and LsVit2 could also be found in maturing oocytes and developing embryos and early larval stages. LsVit2 was found to be processed into 2 smaller fragments, whereas LsVit1 was found to be full length when deposited into the oocytes. Degradation of LsVit1 and LsVit2 was characterised through embryogenesis and the early non-feeding larval stages. Finally, protein content and the level of free amino acids were analysed in embryos and larval stages and their role in nutrition and osmoregulation discussed. In conclusion, our results confirm the role of vitellogenins in reproduction as providers of embryonic and larval nutrition.