In ovo elevated oocyte cortisol content induces innate immune responses in rainbow trout (Oncorhynchus mykiss) early embryonic cells

Abstract

Event Abstract Back to Event In ovo elevated oocyte cortisol content induces innate immune responses in rainbow trout (Oncorhynchus mykiss) early embryonic cells Mao Li1*, Spencer Russell2, John S. Lumsden2 and John F. Leatherland1 1 University of Guelph, Biomedical Sciences, Canada 2 University of Guelph, Pathobiology, Canada In most fish embryos, the functional acquired immunity begins after hatch (1), and the protection of the embryos relies on the innate immunity of early embryo cells (1, 2). The immune suppressive effects of cortisol are well established in the developed organism, but the effects of maternal cortisol on early embryo immunity, and the ontogeny of innate immune components are not well established (2, 3). Lectins and TLRs were studied because they are widely distributed among fish tissues, and responsive to pathogens (5, 6). Naturally-ovulated rainbow trout oocytes were incubated in cortisol-enriched ovarian fluid for 3-h to examine the effects of the cortisol exposure on the ontogeny of innate immunity in rainbow trout embryos. Egg cortisol content was elevated from 4 ng/oocyte (controls - CC) to 5 (C1) and 7.5 ng/oocyte (C2) prior to fertilization (4). Lysozyme activity, intelectin, TLR-5M and TLR-5S gene expression were measured, and the intelectin and ladderlectin localization was examined in embryos using immunohistological [IH] methods. Lysozyme activity was significantly elevated in the C2 treatment group from the zygote until 13-days post fertilization (dpf), but was not affected at 21-dpf. Both intelectin and ladderlectin were present in 12-hours post-fertilization (hpf) (2-cell stage) embryos. But they had differences in response to cortisol exposure, intelectin levels (intensity of staining signal) were elevated in both cortisol treatment groups at 12-hpf and then suppressed between 36- and 48-hpf; ladderlectin was suppressed by both elevated cortisol treatments until 36-hpf compared to controls. Both lectins were distributed cell membranes and among epithelial tissues and brain tissues in late stage embryos. Intelectin mRNA was detected in oocytes and transcript levels were significantly elevated in both cortisol treatment groups relative to the controls after the 3-h incubation. There were no differences among the three treatment groups at 1- and 5-dpf, but intelectin mRNA levels were lower in the cortisol treatment groups at 13-dpf, and the transcript levels in the C2 treatment group were lower than in the CC and C1 treatment groups at 26-dpf. mRNA transcripts for the two TLR-5 genes were present in oocytes; transcript levels were significantly higher in both cortisol treatment groups relative to the controls after the 3 h incubation; TLR-5S mRNA was more abundant than that of TLR-5M mRNA. In conclusion, the ontogeny of the gene expression patterns, and the genes, lectins and lysozyme are response to increased oocyte cortisol content which indicates the importance of innate immunity in the early embryonic cells and embryo development prior to acquired immunity functions in fish. (Supported by NSERC and OMAF to JFL and JSL; NSERC Doctoral Scholarship to ML).