Stress- and xenobiotic-induced changes in early fish embryo gene expression patterns as biomarkers of development and growth in juveniles

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The cytoplasm of the vertebrate oocyte plays a key role in regulating or modifying early gene expression by an embryo that develops from that oocyte, and can influence the phenotype of post-embryonic stages. Despite decades of intensive research in mammals leading to the development of reproductive biotechnologies such as in vitro fertilization (IVF) the epigenetic influences of the ooplasm factors are still poorly understood; embryo deformity rates in IVF-derived mammalian embryos remain high. Much less is known about the role of ooplasm in the early ontogeny of fishes, but since the embryo of most fish species is totally reliant on nutrients in the egg yolk, the influence of the ooplasm is likely to be significant. Moreover, some maternal hormones and some contaminants that are known to disrupt endocrine physiology in adult fish are transferred from maternal blood to the oocytes during the maturation of fish ovaries; this uncontrolled delivery of biologically active hormones and endocrine disrupting compounds may have significant consequences for the early development of the embryo either by acting on hormone receptors, or by inhibiting the clearance of native hormones. We propose to examine the impact of the stress hormone, cortisol, on the expression of key growth-related genes during early embryogenesis; egg cortisol content varies with the maternal plasma hormone levels (and hence stress levels) of the brood-stock, but its actions on embryo development is poorly understood. In addition, we propose to examine the effect of two classes of endocrine disrupting compounds, a xenoestrogen (bisphenol A) and an activator of the hepatic aryl hydrocarbon receptor (TCDD) on the expression of the same genes. The effects of these factors on the acute stress-response, and the expression of growth related genes will be examined in embryos and early stage juveniles.