A novel gene-family involved in spermatophore generation in the economically important salmon louse Lepeophtheirus salmonis

Potential dsRNAs can be delivered to aquatic for defense pathogens

The use of antibiotics to facilitate resistance to pathogens in aquatic animals is a traditional method of pathogen control that is harmful to the environment and human health. RNAi is an emerging technology in which homologous small RNA molecules target specific genes for degradation, and it has already shown success in laboratory experiments. However, further research is needed before it can be applied in aquafarms. Many laboratories inject the dsRNA into aquatic animals for RNAi, which is obviously impractical and very time consuming in aquafarms. Therefore, to enable the use of RNAi on a large scale, the methods used to prepare dsRNA need to be continuously in order to be fast and efficient. At the same time, it is necessary to consider the issue of biological safety. This review summarizes the key harmful genes associated with aquatic pathogens (viruses, bacteria, and parasites) and provides potential targets for the preparation of dsRNA; it also lists some current examples where RNAi technology is used to control aquatic species, as well as how to deliver dsRNA to the target hydrobiont.

Identification and Description of the Key Molecular Components of the Egg Strings of the Salmon Louse (Lepeophtheirus salmonis)

The salmon louse Lepeophtheirus salmonis is a parasite of Atlantic salmon and other salmonids. Every year, it causes high costs for the Norwegian aquaculture industry. While the morphology of the female genital tract has been described, knowledge of the molecular basis of reproduction is very limited. We identified nine genes which are expressed exclusively in the female cement gland, the organ responsible for cement production, which is used to hold the eggs together and keep them attached to their mother in egg strings. Six of these genes encode proteins with signal peptides and probably form the main component of the cement. Two other genes are peroxidases, which are probably important in the cement formation. The last gene is not similar to any known protein, but contains a transmembrane domain. A knockdown of all these genes leads to missing or deformed egg strings, preventing reproduction of the lice. The correct assemblage of the cement in the cement gland is essential for successful reproduction of salmon lice. Similar proteins seem to be present in other copepod species, as well.

Sex-biased gene expression and evolution of candidate reproductive transcripts in adult stages of salmon lice (Lepeophtheirus salmonis)

The salmon louse Lepeophtheirus salmonis (Krøyer 1837) displays numerous sexually dimorphic characteristics. Insights into their underlying molecular components have only recently been explored, which serve to better understand both the basic biology of the louse, associated impacts on drug sensitivity, and evolution of resistance. Expression of 16 L. salmonis genes putatively involved in sexual dimorphism and reproduction were used to determine differences between sexes and better understand responses to mating using RT-qPCR of pre-adult and adult lice. Analysis of these genes revealed the dynamic nature of sex-biased expression across stages. However, female reception of a spermatophore did not appear to impact the expression of these particular genes. Furthermore six of these transcripts and 84 others identified previously in a large-scale louse transcriptomics experiment were used to estimate differences in evolutionary rates and codon-usage bias of sex-related genes using phylogenetic analysis by maximum likelihood (PAML) and codonW. Results suggest male-biased genes are evolving at significantly greater rates than female-biased and unbiased genes as evidenced by higher rates of non-synonymous substitutions and lower codon-usage bias in these genes. These analyses expand our understanding of interactions of sex-biased expression across the pre-adult and adult life stages and provide foundations for better understanding evolutionary differences in sex-biased genes of L. salmonis.

RNAi mediated myosuppressin deficiency affects muscle development and survival in the salmon louse (Lepeophtheirus salmonis)

Muscle activity is regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. In Arthropods, one of the important myoinhibitors is Myosuppressin, belonging to FMRFamide-like peptides, that was shown to have inhibitory effects on visceral muscle contraction and to regulate vital physiological processes including reproduction or feeding. We have identified myosuppressin in salmon louse Lepeophtheirus salmonis (LsalMS) and systematically characterised its function and complex abnormalities emerging after LsalMS knockdown by RNAi in all developmental stages in this species. Immunohistochemistry analysis localized the LsalMS mainly to the central nervous system, but also to the vital organs within the alimentary tract and the reproductive system. The most striking feature of LsalMS deficiency during lice development was severe reduction of the muscle content, with abnormalities detected in both the visceral and skeletal muscles. Moreover, down-regulation of LsalMS affects moulting, spermatophore deposition and feeding by affecting development of the intestinal wall and increasing its contraction frequency.