Project description:A total of 55 individuals were analysed: 15 migratory brown trout (Salmo trutta) individuals from the Redon river, 15 sedentary brown trout (S. trutta) individuals from the Redon river, 15 sedentary brown trout (S. trutta) individuals from the Chevenne river, and 10 Atlantic salmon (S. salar) individuals of a hatchery strain. For each individual, RNA was isolated twice from different parts of the same tissue, independently reverse transcribed into Cy3-labeled cDNA and then probed on two different slides, which leads to total of 110 single slide experiments.
Project description:The proliferative darkening syndrome (PDS) is an annually recurring disease that causes species-specific die-off of brown trout (Salmo trutta fario) with a mortality rate of near 100 % in pre-alpine rivers of central Europe. So far the etiology and causation of this disease is still unclear. The objective of this study was to identify the cause of PDS using a next-generation technology detection pipeline. Following the hypothesis that PDS is caused by an infectious agent, brown trout specimens were exposed to water from a heavily affected pre-alpine river with annual occurrence of the disease. Specimens were sampled over the entire time period from potential infection through death. Transcriptomic analysis (microarray) and RT-qPCR of brown trout liver tissue evidenced strong gene expression response of immune-associated genes. Messenger RNA of specimens with synchronous immune expression profiles were ultra-deep sequenced using next-generation sequencing technology (NGS). Bioinformatic processing of generated reads and gap-filling Sanger re-sequencing of the identified pathogen genome revealed strong evidence that a piscine-related reovirus is the causative organism of PDS. The identified pathogen is phylogenetically closely related to the family of piscine reoviruses (PRV) which are considered as the causation of different fish diseases in Atlantic and Pacific salmonid species such as Salmo salar and Onchorhynchus kisutch. This study also highlights that the approach of first screening immune responses along a timeline in order to identify synchronously affected stages in different specimens which subsequently were ultra-deep sequenced is an effective approach in pathogen detection. In particular, the identification of specimens with synchronous molecular immune response patterns combined with NGS sequencing and gap-filling re-sequencing resulted in the successful pathogen detection of PDS.
Project description:The relevance of immune-endocrine interactions to the regulation of ovarian function in teleosts is virtually unexplored. As part of the innate immune response during infection, a number of cytokines such as tumor necrosis factor α (TNFα) and other immune factors, are produced and act on the reproductive system. However, TNFα is also an important physiological player in the ovulatory process in mammals. In the present study, we have examined for the first time the effects of TNFα in vitro in preovulatory ovarian follicles of a teleost fish, the brown trout (Salmo trutta). In control and recombinant trout TNFα (rtTNFα)-treated granulosa cells, we examined the percentage of apoptosis by flow cytometry analysis and cell viability by propidium iodide (PI) staining. Furthermore, we determined the in vitro effects of rtTNFα on follicle contraction and testosterone production in preovulatory trout ovarian follicles. In addition, we analyzed the gene expression profiles of control and rtTNFα-treated ovarian tissue by microarray and real-time PCR (qPCR) analyses.Treatment with rtTNFα induces ovarian cell apoptosis, decreases granulosa cell viability and stimulates the expression of genes known to be involved in the normal ovulatory process in trout. In addition, rtTNFα causes a significant increase in follicle contraction and testosterone production. Also, using a salmonid-specific microarray platform (SFA2.0 immunochip) we observed that rtTNFα induces the expression of genes known to be involved in inflammation, proteolysis and tissue remodeling. In view of these results, we propose that TNFα could have an important role in the biomechanics of follicle weakening, ovarian rupture and oocyte expulsion during ovulation in trout, primarily through its stimulation of follicular cell apoptosis and the expression of genes involved in follicle wall proteolysis and contraction. Reproductively mature female brown trout (Salmo trutta) from a cultured stock at the Piscifactoria de Bagà (Generalitat de Catalunya, Bagà , Spain) were kept under natural conditions of temperature and photoperiod. Fish at the preovulatory stage (according to the position of the germinal vesicle (GV) in oocytes that were cleared using a solution previously described), were anesthesized in 3-aminobenzoic acid ethyl ester (0.1 g/l; Sigma, Alcobendas, Spain) dissolved in fresh water, and the fish were sacrificed by concussion prior to the collection of the ovaries. The dissected ovaries were immediately used for the various in vitro assays. After dissection, brown trout preovulatory ovaries were placed in Hank´s balanced salt solution (HBSS) and individual ovarian follicles were manually separated with forceps from each ovary on ice, as previously described. To collect ovarian tissue for RNA extraction, preovulatory follicles from each of a total of three females were incubated (400 follicles/50 ml) in HBSS-BSA in the absence or presence of rtTNFα (100 ng/ ml, dissolved directly in HBSS-BSA), at 15ºC for 24 h with gentle shaking (100 rpm). At the end of the incubation follicles (previously de-yolked by gentle pressure) were removed, flash frozen in liquid nitrogen and stored at -80ºC until assayed.