title: Sexual maturation and administration of 17β-estradiol and testosterone induce complex gene expression changes in skin and increase resistance of Atlantic salmon to ectoparasite salmon louse.
abstract: The crustacean ectoparasitic salmon louse (Lepeophtheirus salmonis) is a major problem of Atlantic salmon aquaculture in the Northern hemisphere. Host-pathogen interactions in this system are highly complex. Resistance to the parasite involves variations in genetic background, nutrition, properties of skin, and status of the endocrine and immune systems. This study addressed the relationship between sex hormones and lice infection. Field observation revealed a sharp reduction of lice prevalence during sexual maturation with no difference between male and female fish. To determine if higher resistance against lice was related to sex hormones, post-smolt salmon were administered control feed and feeds containing 17β-estradiol (20 mg/kg) and testosterone (25 mg/kg) during a 3-week pre-challenge period. After challenge with lice, counts were reduced 2-fold and 1.5-fold in fish that received 17β-estradiol and testosterone, respectively. Gene expression analyses were performed from skin of salmon collected in the field trial and from the controlled lab experiment at three time points (end of feeding-before challenge, 3 days post challenge (dpc) and 16 dpc) using oligonucleotide microarray and qPCR. Differential expression was observed in genes associated with diverse biological processes. Both studies revealed similar changes of several antibacterial acute phase proteins; of note was induction of cathelicidin and down-regulation of a defensin gene. Treatment with hormones revealed their ability to modulate T helper cell (Th)-mediated immunity in skin. Enhanced protection achieved by 17β-estradiol administration might in part be due to the skewing of Th responses away from the prototypic anti-parasitic Th2 immunity and towards the more effective Th1 responses. Multiple genes involved in wound healing, differentiation and remodelling of skin tissue were stimulated during maturation but suppressed with sex hormones. Such opposite regulation suggested that these processes were not associated with resistance to the parasite under the studied conditions. Both studies revealed regulation of a suite of genes encoding putative large mucosal proteins found exclusively in fish. Marked decrease of erythrocyte markers indicated reduced circulation while down-regulation of multiple zymogen granule membrane proteins and transporters of cholesterol and other compounds suggested limited availability of nutrients for the parasites.
authors.affiliation: Nofima AS, PO Box 6122, NO-9291 Tromsø, Norway. Electronic address: Aleksei.Krasnov@nofima.no.
authors.forename: Aleksei
authors.initials: A
authors.lastname: Krasnov
authors.affiliation: Nofima AS, PO Box 6122, NO-9291 Tromsø, Norway. Electronic address: Mette.W.Breiland@nofima.no.
authors.forename: Mette S
authors.initials: MS
authors.lastname: Wesmajervi Breiland
authors.affiliation: Nofima AS, PO Box 6122, NO-9291 Tromsø, Norway. Electronic address: Bjarne.Hatlen@nofima.no.
authors.forename: Bjarne
authors.initials: B
authors.lastname: Hatlen
authors.affiliation: Nofima AS, PO Box 6122, NO-9291 Tromsø, Norway; Sechenov Institute of Evolutionary Physiology and Biochemistry, M. Toreza av. 44, Peterburg 194223, Russia. Electronic address: afanserg@mail.ru.
authors.forename: Sergey
authors.initials: S
authors.lastname: Afanasyev
authors.affiliation: SLRC-Sea Lice Research Center, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Box 8146, NO-0033 Oslo, Norway. Electronic address: Stanko.Skugor@nmbu.no.
authors.forename: Stanko
authors.initials: S
authors.lastname: Skugor
mesh_terms: D000728:Androgens / Q000008:administration & dosage; D000818:Animals; D033342:Copepoda / Q000502:physiology*; D004478:Ectoparasitic Infestations / Q000235:genetics / Q000469:parasitology / Q000517:prevention & control*; D004958:Estradiol / Q000008:administration & dosage*; D004967:Estrogens / Q000008:administration & dosage; D005260:Female; D005393:Fish Diseases / Q000235:genetics / Q000469:parasitology / Q000517:prevention & control*; D005786:Gene Expression Regulation; D008297:Male; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020317:Salmo salar / Q000235:genetics / Q000276:immunology* / Q000469:parasitology; D012741:Sexual Maturation / Q000502:physiology*; D012867:Skin / Q000166:cytology / Q000378:metabolism*; D013739:Testosterone / Q000008:administration & dosage*
chemical_list: D000728:Androgens; D004967:Estrogens; D012333:RNA, Messenger; D013739:Testosterone; D004958:Estradiol
keywords: Atlantic salmon; Oligonucleotide microarray; Sea louse; Sex hormones; Skin