Antimicrobial peptides from Salmon salar skin induce frontal filament development and olfactory/cuticle-related genes in the sea louse Caligus rogercresseyi

Abstract

The discovery of key molecules involved in host-recognition has the potential to develop novel tools against the most prevalent pathogens in aquaculture. However, how mucosal surface compounds of teleost fish can modulate the attraction mechanisms of ectoparasites remains unknown. This study evaluated the effect of antimicrobial peptides (AMPs) highly expressed in Salmo salar and Oncorhynchus kisutch during the Caligus rogercresseyi infection. RNA-seq analysis from infested skin tissue revealed that Cathelicidin (CATHL) was the most AMPs expressed in comparison to other AMPs. To evidence morphological and transcriptional modulation of sea lice exposed to AMPs, copepodids were incubated with agar medium containing salmon mucus and CATHL1 or 2, or a combination of these. Interestingly, exposure to CATHL promoted the development of the frontal filament of sea lice, mainly CATHL2 peptide. Significant variations in transcript expressions were observed in chemosensory reception- and cuticle formation-related genes. Thus, copepodids exposed to CATHL2 showed significant increases in the mRNA abundance of cuticle formation genes and chemosensory receptors, mainly ionotropic kainate receptors. These results suggest that CATHL can trigger transcriptional responses in sea lice that are not directly linked with the effects of AMPs. The AMP-mediated activation of ionotropic kainate receptors in C. rogercresseyi raises novel questions regarding the molecular aspects of olfactory signal transduction in the host–parasite interactions. Statement of relevanceUnderstanding of molecules that promote the frontal filament during the sea lice infection can be used to develop novel control tools and to explore nutritional additives able to modulate the AMPs fish mucosal.