“Free-swimming copepodid salmon lice (Lepeophtheirus salmonis) undergo a transcriptomic shift when exposed to salmonid host cues (7254)” Written by diazoma on August 12, 2025. Posted in Uncategorized. Abstract Free-swimming copepodid salmon lice (Lepeophtheirus salmonis) undergo a transcriptomic shift when exposed to salmonid host cues Introduction: The salmon louse (Lepeophtheirus salmonis) is an ectoparasitic copepod responsible for huge economic losses to Atlantic salmon (Salmo salar) aquaculture. Parasitic stages feed upon the host’s skin epithelium, mucus and blood, causing skin damage, physiological stress and increased susceptibility to secondary infections. The free-swimming copepodid finds and attaches to the host, this involving chemosensory detection of salmonid kairomones. Any transcriptomic responses that occur following detection of kairomones by the copepodid, likely reflect processes associated with the transition to a parasitic state. We investigated the transcriptomic profiles of pre-parasitic copepodids exposed to a) 3 concentrations of the semiochemical 6-methyl-5-hepten-2one in seawater (HP), b) Atlantic salmon conditioned seawater (SCW) c) a control comprising untreated seawater (SW), to investigate responsive gene regulation and function. Methods: Age matched groups of copepodids were exposed to SW, SCW and HP for 18 h at 8oC. Samples consisted of pools of 50 copepodids per treatment. RNA was extracted and subjected to strand specific RNAseq analysis (50M paired-end 150bps reads) using NovaSeq X plus. qRT-PCR analysis was conducted for multiple genes of interest identified from highly differentially expressed genes (DEGs) as well as from single-nuclei RNAseq (sn-RNAseq) (Chromium, 10X Genomics). Results: Transcriptomic responses indicated that exposure to SCW induces significant regulation of genes associated with cuticle processing, immunomodulation, antimicrobial action and secretory protease activity. qRT-PCR analysis corroborated the expression profiles of selected genes from the RNA-seq and snRNA seq datasets with 5-30 fold expression changes observed for genes encoding trypsin, histidine rich glycoprotein, prisilkin-like, intrepicalcin-like and matrix metalloproteinase-9 proteins. Principal component analysis (PCA) also indicated a clear inter-group separation between SW, HP and SCW and intra-group separation between doses (HP) and concentration (SCW). Conclusions: Determining the transcriptional shifts of host-cue stimulated copepodids provides greater understanding of the first stages of host-pathogen interaction, as copepodids are exposed to host kairomones during initial infection. Further investigation of the relationship of key differentially expressed transcripts to the process of host infection can pave the way to the development of new tools to disrupt this process, providing novel solutions to the problem of salmon louse infection. Authors MCGOWAN, MICHAEL, UNIVERSITY OF STIRLING, Presenter BRON, JAMES, UNIVERSITY OF STIRLING, Author BEKAERT, MICHAEL, COOKE, Author FIELDS, DAVID, INSTITUTE OF MARINE RESEARCH, Author BROWMAN, HOWARD, INSTITUTE OF MARINE RESEARCH, Author KRASNOV, ALEKSEI, NOFIMA, Author RUIZ-DANIELS, ROSE, UNVIERSITY OF STIRLING, Author SAILSBURY, SARAH, ROSLIN INSTIUTE, Author DINDIAL, ALEXANDER, UNIVERSITY OF STIRLING, Author HORTON, DANIEL, UNIVERSITY OF STIRLING, Author ROBLEDO, DIEGO, ROSLIN INSTITUTE, Author FAST, MARK, UNIVERSITY OF PRINCE EDWARD ISLAND, Author SVEEN, LENE, NOFIMA, Author EZIAMA, NGOZI, UNIVERSITY OF STIRLING, Author ØVERGÅRD, AINA-CATHERINE, UNIVERSITY OF BERGEN, Author MIDTBØ, HELENA, UNIVERSITY OF BERGEN, Author ROBINSON, NICK, NOFIMA, Author WU, XUHANG, MOREDUN RESEARCH INSTITUTE, Author THOMPSON, KIM, MOREDUN RESEARCH INSTITUTE, Author MONAGHAN, SEAN, UNIVERSITY OF STIRLING, Author